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1
Chen, Yan Hong, T. Li, and Jan Ma. "Electrophoretic Deposition of Functionally Graded Monomorph." Key Engineering Materials 314 (July 2006): 89–94. http://dx.doi.org/10.4028/www.scientific.net/kem.314.89.
Анотація:
In the present work, investigation of the functional property of piezoelectric graded monomorph actuator systems is presented. The functional graded actuators were fabricated by electrophoretic deposition (EPD) using pure PZT and doped PZT materials. Actuators developed have shown gradual gradient variation in microstructure. It is noted that trend in microstructural gradient does not represent similar trend in piezoelectric property gradient. The displacement of microstructural graded and both piezoelectric and microstructural graded actuators were measured. The results show that the gradient distribution of the piezoelectric properties is important to improve the electromechanical performance of the actuator.
2
Schmidt, Christopher David, Hans-Jürgen Christ, and Axel Von Hehl. "Hydrogen as a Temporary Alloying Element for Establishing Specific Microstructural Gradients in Ti-6Al-4V." Metals 12, no. 8 (July 28, 2022): 1267. http://dx.doi.org/10.3390/met12081267.
Анотація:
Parts of vehicles, such as landing gear components of aircrafts, are subject to growing demands in terms of sustainability via lightweight design and durability. To fulfill these requirements, the development of thermochemical processes is auspicious. Titanium alloys allow a heat treatment in hydrogen-containing atmosphere for temporary hydrogen alloying, often called thermohydrogen treatment (THT). The investigation presented intends to realize a local microstructure modification of Ti-6Al-4V by means of THT. The study aims to use hydrogen (H) as a promoter for changing the local distribution and morphology of strengthening precipitates during THT as well as the local grain size (microstructural gradient). Both shall improve the fatigue properties of the material after hydrogen degassing. To derive suitable thermohydrogen treatment process parameters, the resulting fatigue crack propagation resistance and fracture toughness after different solution heat treatments are determined experimentally and compared to each other. Moreover, various graded microstructures are evaluated after hydrogen uptake (hydrogenation) and hydrogen degassing (dehydrogenation) using numerically simulated hydrogen concentration profiles, observed hardness curves, metallographically determined microstructure gradients and the corresponding results of the phase analysis by means of X-ray diffraction. The study shows that hydrogenation at 500 °C and dehydrogenation at 750 °C enables the generation of a promising microstructural gradient.
3
Rabin, B. H., and I. Shiota. "Functionally Gradient Materials." MRS Bulletin 20, no. 1 (January 1995): 14–18. http://dx.doi.org/10.1557/s0883769400048855.
Анотація:
This issue of the MRS Bulletin provides an up-to-date look at ongoing research activities within the field of functionally gradient materials (FGM). The term FGM, now widely used by the materials community, originated in Japan in the late 1980s as a description for a class of engineering materials exhibiting spatially inhomogeneous microstructures and properties. Of course, gradient materials are not something new. It must be recognized that humans have extensively utilized materials containing microstructural gradients (either those found in nature or those created through processing) since the earliest days of craftsmanship and engineering construction. Indeed, there are examples of graded materials developed long ago, such as case-hardened steel, which are still in common use today. Contemporary examples of these materials serve in technologically significant applications, as, for example, in thermal-barrier coatings for gas turbines. Nevertheless, what is new and exciting about FGMs is the realization that gradients can be designed at the microstructural level to tailor a material for the specific functional and performance requirements of an intended application. In addition, recent advances in processing are opening the possibility for the extension of the gradient materials concept to new materials systems and engineering problems.The recent resurgence of interest in gradient materials has been driven by the need for improved materials, capable of meeting the demanding performance requirements established by emerging technologies such as the aerospace plane, ceramic engines, and nuclear fusion.
4
Schmidt, Christopher David, Vitali Macin, Peter Schmidt, and Hans-Jürgen Christ. "Generation of Microstructural Gradients for Improved Mechanical Properties via Thermo-Hydrogen Treatment of the Metastable Beta Titanium Alloys Beta CTM and Ti 10V-2Fe-3Al." MATEC Web of Conferences 321 (2020): 12017. http://dx.doi.org/10.1051/matecconf/202032112017.
Анотація:
Structural components must be lightweight and produced resource-saving while still fulfil the increasing durability and reliability requirements. One approach to fulfil these requests is a temporary hydrogen charging of Ti-alloys, which generates lattice distortion and hydrides. The volume difference between hydride precipitates and the alloy matrix results in localized plastic deformation. This triggers recrystallization and enables a finer microstructure as attainable by a conventional heat treatment. The study aims at an elaboration of a thermo-hydrogen treatment that establishes a change in grain size and/or an alteration in distribution and morphology of strengthening secondary α precipitates as a function of the distance to surface (microstructural gradient). The gradient is based on a gradient of the hydride volume fraction. Generally, THT design requires kinetic (temperature dependency of the hydrogen diffusion coefficient DH) in addition to thermodynamic (H/β-Ti-alloy interaction) data, which has been obtained for Ti 3Al-8V-6Cr-4Mo-4Zr and Ti 10V-2Fe-3Al. Subsequent to a solution treatment the variation of hydrogenation time and temperature is operated to establish comparably slight microstructural gradients on these materials. For further investigations it is concluded that materials with less alloying elements ((α+β)-Ti-alloys (e.g.,Ti 6Al-4V)) than these β-Ti-alloys can satisfy the requirements to generate steeper microstructural gradients even better.
5
Ueno, Kouki, Akira Sato, and Hiroyuki Sato. "Formation of Microstructural Gradient of A2017 by RBT at Ambient Temperature." Materials Science Forum 794-796 (June 2014): 1233–38. http://dx.doi.org/10.4028/www.scientific.net/msf.794-796.1233.
Анотація:
Distribution of microstructure and hardness by RBT (Rotary Bending and Tensile) loading at ambient temperature is presented. Grain size is one of the important parameters of microstructures of alloys, and affects mechanical characteristics depending on deformation conditions. At higher temperatures, coarsening of grain size improves creep strength, while the finer improve tensile strength at ambient temperature. Grain size shows opposite effect on strength of alloys depending on temperatures and not always possible to improve strength both at ambient and high temperatures. Authors have attempted microstructural control by formation of distribution of plastic strain prior to heat treatment of aluminum alloys to obtain well-balanced strength both at high and ambient temperatures. In this report, distribution of grain size and hardness in 2017 aluminum by RBT loading are presented, and compared with results in 1070 reported previously. RBT loading equipment is designed for combined loading by rotary bending and static tensile loading to distribute plastic strain. In 2017 alloy, obtained microstructure after suitable heat treatment show distribution of hardness, while grain size show homogeneous distribution. The distributions, however, are different from that in 1070 alloy.
6
Pei, Wanrong, Tongde Wu, Zhiwen Wang, Yunlei Jiang, Chuanping Zhou, Rougang Zhou, and Yongping Gong. "Reflection of Elastic Waves in Dipolar Gradient Half-Space under the Control of External Magnetic Field." Applied Sciences 14, no. 1 (December 31, 2023): 376. http://dx.doi.org/10.3390/app14010376.
Анотація:
This paper investigated the reflection of plane waves at the interface of dipolar gradient elastic solids under the control of an external magnetic field. This study focused on the increasing influence of the microstructural effect as the incident wavelength approaches the characteristic length of the microstructure or at higher frequencies. Initially, the dispersion equation for the propagation of elastic waves was derived from the dipole strain gradient theory and Maxwell’s electromagnetic theory. Subsequently, the amplitude ratios of various reflected waves to incident P-waves and incident SV-waves were calculated based on the interface conditions. Finally, the numerical results were used to discuss the impact of the external magnetic field and microstructural characteristic length on the propagation of the reflected wave. It was observed that the microstructural effect generated new wave modes and introduced dispersion characteristics into the elastic waves. Conversely, the external magnetic field primarily influences the amplitude of the elastic wave propagation via the Lorentz force without creating new wave modes or affecting the dispersion properties of the elastic wave in the dipolar gradient elastic solid.
7
Seo, Seongji, and Jiyong Park. "Annealing Heat Treatment for Homogenizing the Microstructure and Mechanical Properties of Electron-Beam-Welded Thick Plate of Ti-6Al-4V Alloy." Materials 16, no. 23 (November 29, 2023): 7423. http://dx.doi.org/10.3390/ma16237423.
Анотація:
In the application of Ti-6Al-4V to aerospace structural components, when welding thick plates similar of the thickness of the components, microstructure and hardness gradients emerge between the base material (BM) and the joint. This leads to the issue of significant stress concentration in the BM under tensile stress. To address this problem through post-welding heat treatment, this study conducted heat treatments at temperatures both below (mill annealing, MA) and above the beta-transus temperature (beta annealing, BA) on electron-beam weldments of 18 mm thickness Ti-6Al-4V plates. Subsequently, microstructures and hardness were analyzed at different depths from the upper surface and areas (fusion zone (FZ), heat-affected zone (HAZ), and BM), and tensile properties were measured at various depths. The results indicated that α′ observed in FZ and HAZ was resolved through both MA and BA. Particularly after BA, the microstructural gradient that persisted even after MA completely disappeared, resulting in the homogenization of widmanstätten α + β. Consequently, after BA, the hardness gradient in each zone also disappeared, and the tensile strength was higher than in just-welded and MA heat-treated plates.
8
Liu, Mulin, Naoki Takata, Asuka Suzuki, and Makoto Kobashi. "Effect of Heat Treatment on Gradient Microstructure of AlSi10Mg Lattice Structure Manufactured by Laser Powder Bed Fusion." Materials 13, no. 11 (May 29, 2020): 2487. http://dx.doi.org/10.3390/ma13112487.
Анотація:
The present study addressed the effect of heat treatment process on microstructure of an AlSi10Mg lattice structure with a body-centered cubic unit cell manufactured via laser powder bed fusion (LPBF). The as-manufactured lattice specimen exhibited a unique cellular structure composing of primary α-Al phases bounded by α-Al/Si eutectic microstructure. A gradient microstructure (continuous microstructural changes) was found in the node and strut portions composed of the lattice specimen. The microstructure appears more equiaxed and coarser with approaching the bottom surface of both portions. The continuous microstructural changes contributed to a variation in hardness measured at different locations in the as-manufactured lattice specimen. Si particles finely precipitate in the primary α-Al phases, and eutectic Si particle coarsening occurs at an elevated temperature of 300 °C. The microstructural coarsening is more pronounced at a higher temperature. A number of significantly coarsened Si particles and a stable Fe-containing intermetallic phase (β-AlFeSi) were observed at all locations in 530 °C solution-treated specimen. The homogenous microstructure results in a constant hardness value independent of the location in the lattice specimen. These results provide new insights to control the compressive properties of the AlSi10Mg lattice structure manufactured via LPBF by subsequent heat treatment processes.
9
Liu, Yao, and Songlin Cai. "Gradients of Strain to Increase Strength and Ductility of Magnesium Alloys." Metals 9, no. 10 (September 22, 2019): 1028. http://dx.doi.org/10.3390/met9101028.
Анотація:
A strain gradient was produced in an AZ31B magnesium alloy through a plastic deformation of pure torsion at a torsional speed of π/2 per second. Compared with the base material and with the alloy processed by conventional severe plastic deformation, the magnesium alloy provided with a strain gradient possesses high strength preserving its ductility. Microstructural observations show that strain gradient induces the formation of an inhomogeneous microstructure characterized by statistically stored dislocation (SSD) density gradient and geometrically necessary dislocation (GND). GNDs and dislocation density gradient provide extra strain hardening property, which contributes to the improvement of ductility. The combination of SSD density gradient and GND can simultaneously improve the strength and ductility of magnesium alloy.
10
Mishnaevsky, Leon. "Computational Analysis of the Effects of Microstructures on Damage and Fracture in Heterogeneous Materials." Key Engineering Materials 306-308 (March 2006): 489–94. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.489.
Анотація:
3D FE (finite element) simulations of the deformation and damage evolution of particle reinforced composites are carried out for different microstructures of the composites. Several new methods and programs for the automatic reconstruction of 3D microstructures of composites on the basis of the geometrical description of microstructures as well as on the basis of the voxel array data have been developed and tested. Different methods of reconstruction and generation of finite element models of 3D microstructures of composite materials (geometry-based and voxel array based) are discussed and compared. It was shown that FE analyses of the elasto-plastic deformation and damage of composite materials using the microstructural models of materials generated with these methods yield very close results. Numerical testing of composites with random, regular, clustered and gradient arrangements of spherical particles is carried out. The fraction of failed particles and the tensile stress-strain curves were determined numerically for each of the microstructures. It was found that the rate of damage growth as well as the critical applied strain, at which the damage growth in particles begins, depend on the particle arrangement, and increase in the following order: gradient < random < regular < clustered microstructure.
11
Roeder, Ryan K., Keith J. Bowman, and Kevin P. Trumble. "Texture and Microstructure Development in Al2O3-Platelet Reinforced Ce-ZrO2/Al2O3 Laminates Produced by Centrifugal Consolidation." Textures and Microstructures 24, no. 1-3 (January 1, 1995): 43–52. http://dx.doi.org/10.1155/tsm.24.43.
Анотація:
A dispersed, low-solids-fraction suspension containing Ce-ZrO2, fine Al2O3 and 5 vol% Al2O3-platelets was segregated using centrifugal consolidation to produce functionally gradient laminates (FGLs). Platelet alignment facilitated efficient packing of highly anisometric platelets to high densities. The complexity and anisotropy of the microstructure warrants a quantitative analysis of the microstructural evolution prior to any property evaluation. Quantitative image analysis was used to examine changes in the volume fraction, dimensional anisotropy, and gradient of pores and platelets with sintering time. In all cases, special attention was given to the effects of texture during microstructural evolution. Platelet alignment enhanced densification via anisotropic shrinkage, overcoming constraint that otherwise inhibits densification in platelet-containing materials. Also, platelet alignment and microstructural design were used to initiate and control anisotropic grain growth. Platelet growth (at the expense of smaller particles of the same phase) during annealing promoted further phase segregation and produced higher platelet content composites consisting of larger platelets, without having to consolidate high contents of large platelets.
12
Rodríguez-Parra, Jesús, Rodrigo Moreno, and Isabel Nieto. "Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting." Journal of the Serbian Chemical Society 77, no. 12 (2012): 1775–85. http://dx.doi.org/10.2298/jsc121018132r.
Анотація:
Freeze casting is a well-known shaping technique to produce materials with directional porosity. One of the major problems is the difficulty to control the cooling rate thus leading to gradients in pore size and homogeneity. This work deals with the manufacture of alumina ceramics with directional porosity by freeze casting of aqueous suspensions. An experimental set-up was prepared in order to apply different cooling rates. Freeze casting tests were done with an aqueous alumina suspension after optimization of its rheological behavior. The porosity and microstructural features of sintered bodies produced under different experimental conditions were studied and analyzed. It is concluded that the cooling rate influences the microstructure while final temperature has a much lower influence. Also, the microstructural analysis shows that there is a gradient in the directionality of pores, being lower at the bottom and the top and higher in the central region of the specimens.
13
Abu Al-Rub, Rashid K., Najmul H. Abid, Mahmood Ettehad, and Anthony N. Palazotto. "Microstructural Modeling of Dual Phase Steel Using a Higher-Order Gradient Plasticity-Damage Model." Applied Mechanics and Materials 784 (August 2015): 119–28. http://dx.doi.org/10.4028/www.scientific.net/amm.784.119.
Анотація:
This work focuses on the application of a higher-order gradient-dependent plasticity-damage model for microstructural modeling of dual-phase (DP) steels. Damage evolution is governed by the evolution of a nonlocal plasticity measure which is a function of the local equivalent plastic strain rate and its corresponding first-order gradient. Different RVEs of DP microstructures are virtually generated and simulated in order to predict the macroscopic mechanical response. Size effects and additional hardening due to evolution of geometrically necessary dislocations are predicted.
14
Liu, Tie, Qiang Wang, Zhong Ying Wang, Dong Gang Li, and Ji Cheng He. "Alignment of Primary Al3Ni Phases in Hypereutectic Al-Ni Alloys with Various Compositions under High Magnetic Field Gradients." Materials Science Forum 649 (May 2010): 165–69. http://dx.doi.org/10.4028/www.scientific.net/msf.649.165.
Анотація:
The microstructural changes of the primary Al3Ni phases in hypereutectic Al-Ni alloys solidified under various high magnetic field gradients were investigated. It was found that the application of a magnetic field gradient induced an aligned structure of the primary Al3Ni phases similar to those in a high uniform magnetic field. However, the high magnetic field gradient showed more obvious effect on the alignment of the primary Al3Ni phases than the uniform magnetic field, although this effect strongly depended on the alloy composition.
15
Lombardo, Mariateresa, and Harm Askes. "Elastic wave dispersion in microstructured membranes." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 466, no. 2118 (January 13, 2010): 1789–807. http://dx.doi.org/10.1098/rspa.2009.0516.
Анотація:
The effect of microstructural properties on the wave dispersion in linear elastic membranes is addressed in this paper. A periodic spring-mass lattice at the lower level of observation is continualized and a gradient-enriched membrane model is obtained to account for the characteristic microstructural length scale of the material. In the first part of this study, analytical investigations show that the proposed model is able to correctly capture the physical phenomena of wave dispersion in microstructured membrane which is overlooked by classical continuum theories. In the second part, a finite-element discretization of microstructured membrane is formulated by introducing the pertinent inertia and stiffness terms. Importantly, the proposed modifications do not increase the size of the problem compared wiith classical elasticity. Numerical simulations confirm that the vibrational properties are affected by the microstructural characteristics of the material, particularly in the high-frequency regime.
16
Koontz, John T., Guillaume T. Charras, and Robert E. Guldberg. "A Microstructural Finite Element Simulation of Mechanically Induced Bone Formation." Journal of Biomechanical Engineering 123, no. 6 (June 7, 2001): 607–12. http://dx.doi.org/10.1115/1.1406951.
Анотація:
A finite element method to simulate the formation of an interconnected trabecular bone microstructure oriented with respect to applied in vivo mechanical forces is introduced and quantitatively compared to experimental data from a hydraulic bone chamber implant model. Randomly located 45 μm mineralized nodules were used as the initial condition for the model simulations to represent an early stage of intramembranous bone formation. Boundary conditions were applied consistent with the mechanical environment provided by the in vivo bone chamber model. A two-dimensional repair simulation algorithm that incorporated strain energy density (SED), SED gradient, principal strain, or principal strain gradient as the local objective criterion was utilized to simulate the formation of an oriented trabecular bone microstructure. The simulation solutions were convergent, unique, and relatively insensitive to the assumed initial distribution of mineralized nodules. Model predictions of trabecular bone morphology and anisotropy were quantitatively compared to experimental results. All simulations produced structures that qualitatively resembled oriented trabecular bone. However, only simulations utilizing a gradient objective criterion yielded results quantitatively similar to in vivo observations. This simulation approach coupled with an experimental model that delivers controlled in vivo mechanical stimuli can be utilized to study the relationship between physical factors and microstructural adaptation during bone repair.
17
Kumar, Dharmesh, Sridhar Idapalapati, Wei Wang, and Srikanth Narasimalu. "Effect of Surface Mechanical Treatments on the Microstructure-Property-Performance of Engineering Alloys." Materials 12, no. 16 (August 7, 2019): 2503. http://dx.doi.org/10.3390/ma12162503.
Анотація:
Fatigue is a dominant failure mechanism of several engineering components. One technique for increasing the fatigue life is by inducing surface residual stress to inhibit crack initiation. In this review, a microstructural study under various bulk (such as severe plastic deformation) and surface mechanical treatments is detailed. The effect of individual microstructural feature, residual stress, and strain hardening on mechanical properties and fatigue crack mechanisms are discussed in detail with a focus on nickel-based superalloys. Attention is given to the gradient microstructure and interface boundary behavior for the mechanical performance. It is recommended that hybrid processes, such as shot peening (SP) followed by deep cold rolling (DCR), could enhance fatigue life. The technical and scientific understanding of microstructural features delineated here could be useful for developing materials for fatigue performance.
18
Xu, Mingxiu, Harm Askes, Xinchun Shang, and Inna M. Gitman. "Microscale size effects in piezomagnetic material for the anti-plane problem." Acta Mechanica 232, no. 11 (October 7, 2021): 4609–23. http://dx.doi.org/10.1007/s00707-021-03071-9.
Анотація:
AbstractA continuum model of piezomagnetic material with strain, magnetic and piezomagnetic coupling gradient effects is proposed using a variational principle in this work. This model is employed to an anti-plane problem, and a general solution is constructed in polar coordinates. Special attention is paid to microstructural effects on the magnetic and mechanical response in an infinite piezomagnetic medium with a void. It is found that the microstructural length scales have a significant influence on the mechanic and magnetic fields. The three length scales (corresponding to strain, magnetic and piezomagnetic coupling gradients) are indispensable to describe the nonlocal effects of piezomagnetism. Additionally, controlling the direction and magnitude of the magnetic field at the edge of the void can be achieved by adjusting the microstructural length scales of the piezomagnetic medium.
19
Zöllner, D. "Impact of a strong temperature gradient on grain growth in films." Modelling and Simulation in Materials Science and Engineering 30, no. 2 (January 7, 2022): 025010. http://dx.doi.org/10.1088/1361-651x/ac44a8.
Анотація:
Abstract The migration of grain boundaries and, therewith, the phenomenon of grain growth depend strongly on the annealing temperature. Generally, higher temperatures are associated with higher mobilities of the boundaries and therewith faster microstructural coarsening. In the present study, the influence of a strong temperature gradient on grain growth in thin films is investigated. To that aim, a modified three-dimensional Potts model algorithm is employed, where the annealing temperature changes with the thickness of the sample taking grain boundary mobility and energy into account. The resulting drag effect has serious consequences for the temporal and spatial evolution of the grain microstructure.
20
Miller, D. A., and E. E. Adams. "A microstructural dry-snow metamorphism model for kinetic crystal growth." Journal of Glaciology 55, no. 194 (2009): 1003–11. http://dx.doi.org/10.3189/002214309790794832.
Анотація:
AbstractHistorically, dry-snow metamorphism has been classified by the thermal environment and thermodynamic processes in a snowpack. Snow experiencing predominantly macroscopic isothermal conditions develops different microstructure than snow subjected to large temperature gradients. As such, much previous research has been categorized by and limited to specific thermal conditions. The current research expands a generalized approach for the movement of heat and mass to include a snow crystal kinetic growth model. An existing spiral defect propagation theory for kinetic growth on simple faceted geometry is utilized. Primary crystal habit as a function of temperature is incorporated. A model of heat and mass transfer through an ice and pore structure is coupled with phase-change thermodynamics during kinetic growth. A kinetic growth microstructure model is developed and integrated into heat and mass transfer representations, which are solved using finite-difference techniques. The kinetic morphology model approximates frequently observed hopper-type crystals. The snow microstructure is allowed to change at every step, resulting in a transient description of kinetic growth metamorphism. Variable kinetic growth rates are demonstrated based on temperature and on crystallographic orientation relative to a temperature gradient. Crystals preferentially aligned with the temperature gradient have significantly higher growth rates, supporting previous observations of predominant crystal habits developing under temperature gradient conditions. Grain-size dispersion increase with time is demonstrated and supported experimentally in the literature. A dominant grain growth theory based on crystallographic orientation that has been previously postulated is supported. A broad range of metamorphic geometric parameters and thermal conditions may now be simulated with a single model.
21
Xu, Xiao Jing, Xin Lin, Jing Chen, Fei He, and Wei Dong Huang. "Laser Rapid Forming of Ti-Ni Functionally Graded Alloy." Materials Science Forum 561-565 (October 2007): 227–30. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.227.
Анотація:
Ti-Ni based functionally graded alloy is a kind of the promising material, which has potential to be used in aero engines. Using laser rapid forming, a Ti-Ni graded alloy with a continuous compositional gradient from pure Ti to Ti-50wt.%Ni were fabricated. On comparison with the graded alloy, a series of homogenous deposits with the typical composition between pure Ti to Ti-50wt.%Ni were also laser rapid formed. The phase evolution along the compositional gradient direction in the graded alloy is: α+β→β+Ti2Ni →(TiNi +Ti2Ni)+ TiNi; and the phase evolution in the corresponding compositional homogeneous deposit is: α+β→ β+(β+Ti2Ni)→ β+Ti2Ni+(β+Ti2Ni)→ (TiNi+Ti2Ni)+TiNi. The phase transformation and microstructural evolution along the compositional gradient were analyzed by using the microstructure selection map.
22
Borkar, Hemant, Salem Seifeddine, and Anders E. W. Jarfors. "Microstructure analysis of Al–Si–Cu alloys prepared by gradient solidification technique." International Journal of Modern Physics B 29, no. 10n11 (April 23, 2015): 1540015. http://dx.doi.org/10.1142/s0217979215400159.
Анотація:
Al – Si – Cu alloys were cast with the unique gradient solidification technique to produce alloys with two cooling rates corresponding to secondary dendrite arm spacing (SDAS) of ~9 and ~27 μm covering the microstructural fineness of common die cast components. The microstructure was studied with optical microscopy and scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) and electron backscattered diffraction (EBSD). The alloy with higher cooling rate, lower SDAS, has a more homogeneous microstructure with well distributed network of eutectic and intermetallic phases. The results indicate the presence of Al – Fe – Si phases, Al – Cu phases and eutectic Si particles but their type, distribution and amount varies in the two alloys with different SDAS. EBSD analysis was also performed to study the crystallographic orientation relationships in the microstructure. One of the major highlights of this study is the understanding of the eutectic formation mechanism achieved by studying the orientation relationships of the aluminum in the eutectic to the surrounding primary aluminum dendrites.
23
Calonne, N., F. Flin, C. Geindreau, B. Lesaffre, and S. Rolland du Roscoat. "Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy." Cryosphere 8, no. 6 (December 5, 2014): 2255–74. http://dx.doi.org/10.5194/tc-8-2255-2014.
Анотація:
Abstract. We carried out a study to monitor the time evolution of microstructural and physical properties of snow during temperature gradient metamorphism: a snow slab was subjected to a constant temperature gradient in the vertical direction for 3 weeks in a cold room, and regularly sampled in order to obtain a series of three-dimensional (3-D) images using X-ray microtomography. A large set of properties was then computed from this series of 3-D images: density, specific surface area, correlation lengths, mean and Gaussian curvature distributions, air and ice tortuosities, effective thermal conductivity, and intrinsic permeability. Whenever possible, specific attention was paid to assess these properties along the vertical and horizontal directions, and an anisotropy coefficient defined as the ratio of the vertical over the horizontal values was deduced. The time evolution of these properties, as well as their anisotropy coefficients, was investigated, showing the development of a strong anisotropic behavior during the experiment. Most of the computed physical properties of snow were then compared with two analytical estimates (self-consistent estimates and dilute beds of spheroids) based on the snow density, and the size and anisotropy of the microstructure through the correlation lengths. These models, which require only basic microstructural information, offer rather good estimates of the properties and anisotropy coefficients for our experiment without any fitting parameters. Our results highlight the interplay between the microstructure and physical properties, showing that the physical properties of snow subjected to a temperature gradient cannot be described accurately using only isotropic parameters such as the density and require more refined information. Furthermore, this study constitutes a detailed database on the evolution of snow properties under a temperature gradient, which can be used as a guideline and a validation tool for snow metamorphism models at the micro- or macroscale.
24
ÇADIRLI, E., and H. KAYA. "DENDRITIC GROWTH OF THE BINARY SUCCINONITRILE-CAMPHOR SYSTEM." Surface Review and Letters 14, no. 06 (December 2007): 1169–79. http://dx.doi.org/10.1142/s0218625x07010767.
Анотація:
Succinonitrile (SCN)–2 wt% Camphor (CAMP) alloy was unidirectionally solidified with a constant temperature gradient (G = 3.01 K/mm ) at different growth rates (V = 6.5–113 μ m/s ) and with a constant growth rate (V = 6.5 μ m/s ) at different temperature gradients (G = 1.93 - 3.01 K/mm ). Microstructural parameters (primary dendrite arm spacings, λ1, secondary dendrite arm spacings, λ2, dendrite tip radius, R, and mushy zone depth, d) were measured as a function of growth rate and temperature gradient. The experimental results have been compared with theoretical models and previous experimental works. The stability constant (σ) for this alloy system was calculated and compared with similar experimental results.
25
Niksiar, Pooya, Frances Su, Michael Frank, Taylor Ogden, Steven Naleway, Marc Meyers, Joanna McKittrick, and Michael Porter. "External Field Assisted Freeze Casting." Ceramics 2, no. 1 (March 24, 2019): 208–34. http://dx.doi.org/10.3390/ceramics2010018.
Анотація:
Freeze casting under external fields (magnetic, electric, or acoustic) produces porous materials having local, regional, and global microstructural order in specific directions. In freeze casting, porosity is typically formed by the directional solidification of a liquid colloidal suspension. Adding external fields to the process allows for structured nucleation of ice and manipulation of particles during solidification. External control over the distribution of particles is governed by a competition of forces between constitutional supercooling and electromagnetism or acoustic radiation. Here, we review studies that apply external fields to create porous ceramics with different microstructural patterns, gradients, and anisotropic alignments. The resulting materials possess distinct gradient, core–shell, ring, helical, or long-range alignment and enhanced anisotropic mechanical properties.
26
Zhao, Yu, Ruobing Wang, Jian Zhang, Muhammad Imran Farid, Wenzheng Wu, and Tianbiao Yu. "Evolution of CrCx Ceramic Induced by Laser Direct Energy Deposition Multilayered Gradient Ni204-dr60 Coating." Materials 16, no. 21 (October 26, 2023): 6865. http://dx.doi.org/10.3390/ma16216865.
Анотація:
The manufacturing process for many large components of machines leads to a difference in their properties and performances based on changes in location. Functionally graded materials can meet these requirements and address the issue of generation and expansion of interface cracks. Ni204–dr60 gradient coatings were successfully fabricated using laser direct energy deposition (LDED). Microstructure mechanism evolution and microhardness of the gradient coating were comprehensively investigated. The change in the precipitated phase at the grain boundary and the intergranular zones resulted in a change in microstructural characteristics and also affected the microhardness distribution. The reinforced phase of the Ni204 → dr60 gradient zone from Ni204 to dr60 gradually precipitated and was rich in Mo and Nb phase, lath-shaped CrCx phase, network-shaped CrCx phase, block shape (Ni, Si) (C, B) phase, block CrCx phase, and block Cr (B, C) phase. The gradient coating thus acts as a potential candidate to effectively solve the problem of crack generation at the interface of dr60 and the substrate.
27
Nomoto, Sukeharu, Masahito Segawa, and Makoto Watanabe. "Non- and Quasi-Equilibrium Multi-Phase Field Methods Coupled with CALPHAD Database for Rapid-Solidification Microstructural Evolution in Laser Powder Bed Additive Manufacturing Condition." Metals 11, no. 4 (April 13, 2021): 626. http://dx.doi.org/10.3390/met11040626.
Анотація:
A solidification microstructure is formed under high cooling rates and temperature gradients in powder-based additive manufacturing. In this study, a non-equilibrium multi-phase field method (MPFM), based on a finite interface dissipation model, coupled with the Calculation of Phase Diagram (CALPHAD) database, was developed for a multicomponent Ni alloy. A quasi-equilibrium MPFM was also developed for comparison. Two-dimensional equiaxed microstructural evolution for the Ni (Bal.)-Al-Co-Cr-Mo-Ta-Ti-W-C alloy was performed at various cooling rates. The temperature-γ fraction profiles obtained under 105 K/s using non- and quasi-equilibrium MPFMs were in good agreement with each other. Over 106 K/s, the differences between the non- and quasi-equilibrium methods grew as the cooling rate increased. The non-equilibrium solidification was strengthened over a cooling rate of 106 K/s. Columnar-solidification microstructural evolution was performed at cooling rates of 5 × 105 K/s to 1 × 107 K/s at various temperature gradient values under a constant interface velocity (0.1 m/s). The results show that, as the cooling rate increased, the cell space decreased in both methods, and the non-equilibrium MPFM was verified by comparing with the quasi-equilibrium MPFM. Our results show that the non-equilibrium MPFM showed the ability to simulate the solidification microstructure in powder bed fusion additive manufacturing.
28
Kunioshi, Clarice Terui, Olandir Vercino Correa, and Lalgudi Venkataraman Ramanathan. "Gradient Nickel – Alumina Composite Coatings." Materials Science Forum 530-531 (November 2006): 261–68. http://dx.doi.org/10.4028/www.scientific.net/msf.530-531.261.
Анотація:
Particle reinforced metal matrix composite (MMC) coatings have been developed due to property combinations such as increased hardness, high creep/fatigue resistance as well as superior wear and oxidation resistance. MMC coatings can be produced by various techniques, which include powder metallurgy (plasma spray and HVOF processes), liquid metal processes and electrodeposition. This paper presents the development of the electrodeposition process to obtain nickel-alumina composites. The process conditions were optimized and based on these gradient nickel-alumina composites were prepared. Microstructural characterization and hardness determinations were carried out. The effect of process parameters on the amount and distribution of alumina particles as well as morphology of the deposits with and without alumina gradients are presented and discussed.
29
Silva, Adrina P., Pedro R. Goulart, José Eduardo Spinelli, and Amauri Garcia. "Microstructural Evolution during the Directional Transient Solidification of a Hypomonotectic Al-0.9wt%Pb Alloy." Materials Science Forum 730-732 (November 2012): 829–34. http://dx.doi.org/10.4028/www.scientific.net/msf.730-732.829.
Анотація:
In the present study a hypomonotectic Al-0.9wt%Pb alloy was directionally solidified under transient heat flow conditions and the microstructure evolution was analyzed. The solidification thermal parameters such as the growth rate, the cooling rate and the temperature gradient were experimentally determined by cooling curves recorded by thermocouples positioned along the casting length. The monotectic structure was characterized by metallography and a microstructural transition was observed. From the casting cooled surface up to a certain position in the casting the microstructure was characterized by well-distributed Pb-rich droplets in the aluminum-rich matrix, followed by a mixture of fibers and strings of pearls from this point to the top of the casting. The interphase spacing (λ) and the diameter of Pb-rich particles were also measured along the casting length and experimental growth laws relating these microstructural features to the experimental thermal parameters are proposed.
30
Li, Runguang, Youkang Wang, Xiaojing Liu, Shilei Li, Qing Tan, Wenjun Liu, Xing Fang, and Yan-Dong Wang. "Micromechanical behaviors related to confined deformation in pure titanium." MATEC Web of Conferences 321 (2020): 12018. http://dx.doi.org/10.1051/matecconf/202032112018.
Анотація:
Confined deformation, e.g. mechanical twinning, shear banding, and Lüders banding, etc. was extensively observed in metals and alloys with low stacking-fault energies, especially under complex loadings, governing the mechanical properties. It is often accompanied with gradient microstructures to accommodate the stress concentrations. Understanding the micromechanical behaviors of structural materials having confined deformation is important for evaluating the structural stabilities of engineering components. Synchrotron-based techniques provide powerful tools for multiscale microstructural characterization owing to their good resolution in real/reciprocal space, fast data collection/processing and flexible application scenarios. In this paper, the synchrotron-based high-energy X-ray diffraction (HE-XRD) and microdiffraction (μXRD) techniques in combination with traditional characterization methods are used to reveal the deformational gradient structures/stresses under different loading modes in multiscale. The structure/stress gradients induced by laser shot peening treatment and the deformation twins generated during uniaxial tensile loading in pure titanium were systematically studied by HE-XRD and μXRD, in order to elucidate the accommodating role of the deformational structures subjected to various confined scenarios. The new finding regarding the micromechanical behaviors related to confined deformation contributes to the in-depth understanding of related complex deformation behaviors.
31
An, Xinlai, Weikang Bao, Zuhe Zhang, Zhouwen Jiang, Shengyun Yuan, Zesheng You, and Yong Zhang. "Gradient Enhanced Strain Hardening and Tensile Deformability in a Gradient-Nanostructured Ni Alloy." Nanomaterials 11, no. 9 (September 18, 2021): 2437. http://dx.doi.org/10.3390/nano11092437.
Анотація:
Gradient-nanostructured material is an emerging category of material with spatial gradients in microstructural features. The incompatibility between gradient nanostructures (GNS) in the surface layer and coarse-grained (CG) core and their roles in extra strengthening and strain hardening have been well elucidated. Nevertheless, whether similar mechanisms exist within the GNS is not clear yet. Here, interactions between nanostructured layers constituting the GNS in a Ni alloy processed by surface mechanical rolling treatment were investigated by performing unique microtension tests on the whole GNS and three subdivided nanostructured layers at specific depths, respectively. The isolated nanograined layer at the topmost surface shows the highest strength but a brittle nature. With increasing depths, isolated layers exhibit lower strength but enhanced tensile plasticity. The GNS sample’s behavior complied more with the soft isolated layer at the inner side of GNS. Furthermore, an extra strain hardening was found in the GNS sample, leading to a greater uniform elongation (>3%) as compared to all of three constituent nanostructured layers. This extra strain hardening could be ascribed to the effects of the strain gradients arising from the incompatibility associated with the depth-dependent mechanical performance of various nanostructured layers.
32
Fernández-Ramos, C., J. C. Sánchez-López, A. Justo, T. C. Rojas, I. Papst, F. Hofer, and A. Fernández. "Microstructural characterization of Ti–TiN/CNx gradient-multilayered coatings." Surface and Coatings Technology 180-181 (March 2004): 526–32. http://dx.doi.org/10.1016/j.surfcoat.2003.10.096.
33
Ceschini, Lorella, Anders E. W. Jarfors, Alessandro Morri, Andrea Morri, Fabio Rotundo, Salem Seifeddine, and Stefania Toschi. "High Temperature Tensile Behaviour of the A354 Aluminum Alloy." Materials Science Forum 794-796 (June 2014): 443–48. http://dx.doi.org/10.4028/www.scientific.net/msf.794-796.443.
Анотація:
The high temperature tensile behaviour of the A354 casting aluminum alloy was investigated also evaluating the influence of secondary dendrite arm spacing (SDAS). Cast specimens were produced through a gradient solidification equipment, obtaining two different classes of SDAS, namely 20-25 µm (fine microstructure) and 40-50 µm (coarse microstructure). After hot isostatic pressing and T6 heat treatment, the samples underwent mechanical characterization both at room and high temperature (200 °C). Results of tensile tests and hardness measurements were related to the microstructural features and fractographic characterization, in order to investigate the effect of microstructure and high temperature exposure on the mechanical behaviour of the alloy.
34
Ghassemali, Ehsan, Anders W. E. Jarfors, Ming Jen Tan, Samuel C. V. Lim, and Mei Qian Chew. "Investigation of Microstructure and Hardness in Microfoming of Pure Copper Pins." Key Engineering Materials 447-448 (September 2010): 381–85. http://dx.doi.org/10.4028/www.scientific.net/kem.447-448.381.
Анотація:
Microforming is defined as the process of production of metallic micro-parts with sub-millimeter dimension. There is as strong interaction between the scale of the microstructure and the size of the part affecting material flow, the so-called “size effect” in microforming processes. Conventional forming rules cannot be directly applied to the micro-scale forming. To better understand the implications for part geometry and properties, further investigation of the material flow related events is necessary. The aim of this work is to investigate microstructural evolution of pure copper during a micro-extrusion process - for production of micro-pins with diameters varying from 300 to 800µm - by means of optical microscope (OM). Qualitative strain gradient distribution could be observed by those pictures. The results showed that change of micro-pins diameter and die angle affect the microstructure and strain distribution of the final product remarkably, that affect the mechanical properties of the pin formed. Furthermore, microhardness results were consistent with the microstructural observations.
35
Tarasov, Vasily E. "General lattice model of gradient elasticity." Modern Physics Letters B 28, no. 07 (March 13, 2014): 1450054. http://dx.doi.org/10.1142/s0217984914500547.
Анотація:
In this paper, new lattice model for the gradient elasticity is suggested. This lattice model gives a microstructural basis for second-order strain-gradient elasticity of continuum that is described by the linear elastic constitutive relation with the negative sign in front of the gradient. Moreover, the suggested lattice model allows us to have a unified description of gradient models with positive and negative signs of the strain gradient terms. Possible generalizations of this model for the high-order gradient elasticity and three-dimensional case are also suggested.
36
di Schino, Andrea, Laura Alleva, and Mauro Guagnelli. "Microstructure Evolution during Quenching and Tempering of Martensite in a Medium C Steel." Materials Science Forum 715-716 (April 2012): 860–65. http://dx.doi.org/10.4028/www.scientific.net/msf.715-716.860.
Анотація:
The microstructural evolution of a quenched medium-C steel during tempering was analyzed by means of Orientation Imaging Microscopy (OIM). The steel was heat treated in order to develop fully martensitic microstructures after quenching with a different prior austenite grain size (AGS). Main results can be summarized as below: A very poor effect of AGS on packet size was found in comparison to bainitic steels. A finer packet was measured at mid-thickness with respect to surface after the quenching process. This phenomenon was attributed to the effect of thermal strain path on phase transformation during quenching. The through-thickness microstructural gradient remains after tempering. High-angle boundary grains do not significantly grow after tempering; on the contrary, low-angle grain boundaries (cells) move, fully justifying the hardness evolution with tempering temperature.
37
Ghasri-Khouzani, Morteza, M. Bruhis, and Joseph Robert McDermid. "Effect of Carbon Gradient on the Microstructure and Mechanical Properties of Fe-22Mn-C TWIP/TRIP Steels." Advanced Materials Research 922 (May 2014): 195–200. http://dx.doi.org/10.4028/www.scientific.net/amr.922.195.
Анотація:
High-manganese austenitic steels are promising emerging automotive steels demonstrating high strength and ductility. The main deformation products observed in these steels are mechanical twins and ε-martensite, where the dominant deformation products vary quite strongly with stacking fault energy (SFE), which in turn is a very strong function of the alloy carbon content. In this research, a Fe-22Mn-0.6C sheet steel was decarburized to achieve a variety of through-thickness C gradients, thereby varying the dominant deformation products through the sheet thickness, with the overall objective of producing unique microstructures and mechanical properties. Microstructural analyses after interrupted tensile testing indicated that the amount of both mechanical twins and ε-martensite increased with increasing true strain, where the deformation products changed from mechanical twins at the higher-C core to ε-martensite at the lower-C surface. The spring-back properties of the C graded steels were also compared with reference to the effect of differential carbon concentration gradient.
38
Lindroos, Matti, Tom Andersson, Jarkko Metsäjoki, and Anssi Laukkanen. "Crystal Plasticity with Micromorphic Regularization in Assessing Scale Dependent Deformation of Polycrystalline Doped Copper Alloys." Crystals 11, no. 8 (August 21, 2021): 994. http://dx.doi.org/10.3390/cryst11080994.
Анотація:
It is planned that doped copper overpacks will be utilized in the spent nuclear fuel repositories in Finland and in Sweden. The assessment of long-term integrity of the material is a matter of importance. Grain structure variations, segregation and any possible manufacturing defects in microstructure are relevant in terms of susceptibility to creep and damage from the loading evolution imposed by its operating environment. This work focuses on studying the microstructure level length-scale dependent deformation behavior of the material, of particular significance with respect to accumulation of plasticity over the extensive operational period of the overpacks. The reduced micromorphic crystal plasticity model, which is similar to strain gradient models, is used in this investigation. Firstly, the model’s size dependent plasticity effects are evaluated. Secondly, different microstructural aggregates presenting overpack sections are analyzed. Grain size dependent hardening responses, i.e., Hall-Petch like behavior, can be achieved with the enhanced hardening associated with the micromorphic model at polycrystalline level. It was found that the nominally large grain size in the base material of the overpack shows lower strain hardening potential than the fine grained region of the welded microstructure with stronger strain gradient related hardening effects. Size dependent regularization of strain localization networks is indicated as a desired characteristic of the model. The findings can be utilized to provide an improved basis for modeling the viscoplastic deformation behavior of the studied copper alloy and to assess the microstructural origins of any integrity concerns explicitly by way of full field modeling.
39
Watanabe, R. "Powder Processing of Functionally Gradient Materials." MRS Bulletin 20, no. 1 (January 1995): 32–34. http://dx.doi.org/10.1557/s0883769400048892.
Анотація:
Powder metallurgical (P/M) processing of FGMs provides a wide range of compositional and microstructural control, along with shape-forming capability. Oxide/metal systems are desirable because this materials combination can be used to easily tailor materials properties. However, there are many problems to be investigated which pertain to each of the processing steps; process innovations will often be required to realize the versatility of this route. In this article, I briefly review the present status of the powder-processing method.Powder metallurgical fabrication of FGMs involves the following sequential steps with a selected material combination of metals and ceramics: determination of the optimum composition profile for an effective thermal-stress reduction; stepwise or continuous stacking of powder premixes according to the predesigned composition profile; compaction of the stacked powder heap and sintering with or without pressurizing. Besides the conventional powder metallurgical routes, a spray deposition method, using mixed powder suspensions and a slurry stacking method, have been developed to form continuously graded stacking. A powder spray stacking apparatus has been devised, which is fully automatic with computer control. Deposited compacts were cold isostatically pressed (CIP) and consolidated by hot isostatic pressing. Their microstructures show that this process provides fine compositional control with desired profiles.Differential temperature sintering by laser-beam heating has been studied to add versatility to the P/M process. The surface of the green compacts is scanned with a laser beam using a predesigned scanning pattern to ensure homogeneous heating over the entire surface.
40
ŞAHİN, MEVLÜT, and EMİN ÇADIRLI. "SOLIDIFICATION CHARACTERISTICS AND MICROSTRUCTURAL EVOLUTION OF Zn-1.26wt.% Al ALLOY." Surface Review and Letters 18, no. 06 (December 2011): 281–88. http://dx.doi.org/10.1142/s0218625x1101476x.
Анотація:
Zn–1.26 wt.% Al alloy was directionally solidified upward with a constant growth rate (V = 16.6 μm/s) in a wide range of temperature gradients (G = 1.94–5.15 K/mm) and with a constant temperature gradient (G = 5.15 K/mm) in a wide range of growth rates (V = 8.3–500 μm/s) with a Bridgman-type directional solidification furnace. Microstructure parameters, the primary dendrite arm spacing (λ1), secondary dendrite arm spacing (λ2) and dendrite tip radius (R), were measured and expressed as functions of G and V by using a linear regression analysis method. It was found that the values of λ1, λ2 and R decrease with increasing values of V and G. The experimental results were compared with the main predictive theoretical and experimental works for dendritic spacings.
41
Mingmuang, Dhammasook, Sukangkana Talangkun, Chawalit Thinvongpitak, Plato Kapranos, Anuprong Pronpijit, and Warunee Bowornkiatkaew. "Effect of Welding Speed on Deformation Behavior of Friction Welded Aluminium/Alumina." Key Engineering Materials 718 (November 2016): 148–53. http://dx.doi.org/10.4028/www.scientific.net/kem.718.148.
Анотація:
The objective of this experiment was to investigate deformation behavior of friction welded aluminium AA6063/alumina. Effect of welding speed on microstructural change and temperature gradient were determined. The result showed effects of welding speed on temperature and grains flow. Microstructures at the interfaces in all conditions exhibited recrystallised grains and hot deformation characteristic. Areas of Heat affected zone (HAZ) decreased with increasing welding speed. Hardness of recrystallised AA6063 grains decreased approximately by 30%. Increasing in amount of deformation increased the fully welded interface areas improving bonding strength of the weld.
42
Felker, Caleb A., John G. Speer, Emmanuel De Moor, and Kip O. Findley. "Hot Strip Mill Processing Simulations on a Ti-Mo Microalloyed Steel Using Hot Torsion Testing." Metals 10, no. 3 (March 3, 2020): 334. http://dx.doi.org/10.3390/met10030334.
Анотація:
Precipitation strengthened, fully ferritic microstructures in low-carbon, microalloyed steels are used in applications requiring enhanced stretch-flange formability. This work assesses the influence of thermomechanical processing on the evolution of austenite and the associated final ferritic microstructures. Hot strip mill processing simulations were performed on a low-carbon, titanium-molybdenum microalloyed steel using hot torsion testing to investigate the effects of extensive differences in austenite strain accumulation on austenite morphology and microstructural development after isothermal transformation. The gradient of imposed shear strain with respect to radial position inherent to torsion testing was utilized to explore the influence of strain on microstructural development for a given simulation, and a tangential cross-section technique was employed to quantify the amount of shear strain that accumulated within the austenite during testing. Greater austenite shear strain accumulation resulted in greater refinement of both the prior austenite and polygonal ferrite grain sizes. Further, polygonal ferrite grain diameter distributions were narrowed, and the presence of hard, secondary phase constituents was minimized, with greater amounts of austenite strain accumulation. The results indicate that extensive austenite strain accumulation before decomposition is required to achieve desirable, ferritic microstructures.
43
Calonne, N., F. Flin, C. Geindreau, B. Lesaffre, and S. Rolland du Roscoat. "Study of a temperature gradient metamorphism of snow from 3-D images: time evolution of microstructures, physical properties and their associated anisotropy." Cryosphere Discussions 8, no. 1 (February 28, 2014): 1407–51. http://dx.doi.org/10.5194/tcd-8-1407-2014.
Анотація:
Abstract. We carried out a study to monitor the time evolution of microstructural and physical properties of snow during a temperature gradient metamorphism: a snow slab was subjected to a constant temperature gradient along the vertical during three weeks in a cold-room, and regularly sampled in order to obtain a set of 3-D images using X-ray microtomography. A large panel of properties was then computed from this series of 3-D images: density, specific surface area, correlation length, mean and Gaussian curvature distributions, air and ice tortuosities, effective thermal conductivity, and intrinsic permeability. Whenever possible, a specific attention was paid to assess these properties along the vertical and horizontal directions, and an anisotropy coefficient defined as the ratio of the vertical over the horizontal values was deduced. The time evolution of these properties, as well as their anisotropy coefficients, was investigated, showing the development of a strong anisotropic behavior during the experiment. Most of the computed physical properties of snow were then compared with two analytical models (Self consistent estimates and Dilutes bed of spheroids) based on the snow density, and the size and anisotropy of the grains through the correlation lengths. These models, which require only basic microstructural information, offer rather good estimates of the properties and anisotropy coefficients for our experiment without any fitting parameters. Our results highlight the interplay between the microstructure and physical properties, showing that the physical properties of snow subjected to a temperature gradient cannot be described accurately using only isotropic parameters such as the density and require more refined information. Furthermore, this study constitutes a detailed database on the evolution of snow properties under a temperature gradient, which can be used as a guideline and a validation tool for snow metamorphism models at the micro or macro scale.
44
Moreira, Aida B., Laura M. M. Ribeiro, and Manuel F. Vieira. "Cast Austenitic Stainless Steel Reinforced with WC Fabricated by Ex Situ Technique." Metals 12, no. 5 (April 21, 2022): 713. http://dx.doi.org/10.3390/met12050713.
Анотація:
In this study, the process of reinforcing austenitic stainless steel with tungsten carbide (WC) particles prepared by an ex situ technique was investigated. More specifically, the effect of microstructural features on the properties of the resulting WC–metal matrix composite (WC-MMC) was studied. For that purpose, porous Fe-WC preforms, prepared by the ex situ technique, were fixed in the mold cavity where they reacted with the molten steel. As confirmed by scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), the resulting composite showed a compositional and microstructural gradient in depth. The microstructure next to the surface is essentially martensite with large WC particles. From this region to the base metal, the dissolution of the original WC particles increased, being closely related to the formation of new carbides: (Fe,W,Cr)6C, (Fe,Cr,W)7C3, and (Fe,Cr,W)23C6. At the interface bonding, a sound microstructure free of discontinuities was achieved. Furthermore, the mechanical tests indicated that the WC-MMC is four times harder and more wear-resistant than the base metal.
45
Padmavardhani, D., A. Gomez, and R. Abbaschian. "Synthesis and microstructural characterization of NiAlAl2O3 functionally gradient composites." Intermetallics 6, no. 4 (January 1998): 229–41. http://dx.doi.org/10.1016/s0966-9795(97)00076-9.
46
Wang, X. B. "Effects of Constitutive Parameters on Thickness of Phase Transformed Adiabatic Shear Band for Ductile Metal Based on Johnson-Cook and Gradient Plasticity Models." Advanced Materials Research 15-17 (February 2006): 609–14. http://dx.doi.org/10.4028/www.scientific.net/amr.15-17.609.
Анотація:
Gradient-dependent plasticity where a characteristic length is involved to consider the microstructural effect (interactions and interplaying among microstructures due to the heterogeneous texture) is introduced into Johnson-Cook model considering the effects of strain-hardening, thermal softening and strain rate sensitivity. Effects of initial static yield stress, strain-hardening coefficient and exponent, strain-rate and thermal-softening parameters on the occurrence of phase transformation and the thickness of phase transformed adiabatic shear band (ASB) in deformed ASB are numerically investigated. Higher initial static yield stress, strain-hardening coefficient, strain-rate parameter and lower strain-hardening exponent lead to earlier occurrence of phase transformation (lower plastic shear strain). Effect of thermal-softening parameter on plastic shear strain corresponding to the onset of phase transformation is not monotonous. Transformed ASB is located at the center of deformed ASB since the position has higher temperature exceeding the temperature of phase transformation. The thickness of transformed ASB increases with decreasing flow shear stress and the increasing tendency becomes slow. For the same flow shear stress, the thickness of transformed ASB is wider for higher initial static yield stress, strain-hardening coefficient and exponent, strain-rate and thermal-softening parameters. Compared with classical elastoplastic theory applicable to completely homogenous material, gradient-dependent plasticity considering the microstructural effect predicts that phase transformation occurs earlier and that the thickness of transformed ASB changes with flow shear stress.
47
Cooke, Kavian O., and Tahir I. Khan. "Microstructure Development during Low-Current Resistance Spot Welding of Aluminum to Magnesium." Journal of Manufacturing and Materials Processing 3, no. 2 (June 14, 2019): 46. http://dx.doi.org/10.3390/jmmp3020046.
Анотація:
Resistance spot welding of aluminum (Al5754) to magnesium (AZ31B) alloys results in the formation of a variety of solidification microstructures and intermetallic compounds that may affect the in-service performance of the weld. This study evaluates the relationship between the welding parameters and the properties of the weld nugget that is formed, and clarifies the morphological and microstructural evolutions within the weld regions during the low-current “small-scale” resistance spot welding of Al5754 to AZ31B. The investigations included a combination of microstructural characterization and thermodynamic analysis of the weld region. The results show that the welding time and clamping force parameters have significant effects on the properties of the nugget formed. The optimal welding parameters were found to be 300 ms welding time and 800 N clamping force. Weld nuggets formed with lower welding time and clamping force were undersized and contained extensive porosity. Meanwhile, a clamping force above 800 N caused gross deformation of the test samples and the expulsion of the molten metal during the welding process. The most significant microstructural changes occurred at the weld/base metal interfaces due to the formation of Al17Mg12 and MgAl2O4 intermetallic compounds as well as significant compositional variation across the weld pool. The thermal gradient across the weld pool facilitated the formation of several microstructural transitions between equiaxed and columnar dendrites.
48
Rahman, Naila, Kathy Xu, Mohammad Omer, Matthew D. Budde, Arthur Brown, and Corey A. Baron. "Test-retest reproducibility of in vivo oscillating gradient and microscopic anisotropy diffusion MRI in mice at 9.4 Tesla." PLOS ONE 16, no. 11 (November 5, 2021): e0255711. http://dx.doi.org/10.1371/journal.pone.0255711.
Анотація:
Background and purpose Microstructure imaging with advanced diffusion MRI (dMRI) techniques have shown increased sensitivity and specificity to microstructural changes in various disease and injury models. Oscillating gradient spin echo (OGSE) dMRI, implemented by varying the oscillating gradient frequency, and microscopic anisotropy (μA) dMRI, implemented via tensor valued diffusion encoding, may provide additional insight by increasing sensitivity to smaller spatial scales and disentangling fiber orientation dispersion from true microstructural changes, respectively. The aims of this study were to characterize the test-retest reproducibility of in vivo OGSE and μA dMRI metrics in the mouse brain at 9.4 Tesla and provide estimates of required sample sizes for future investigations. Methods Twelve adult C57Bl/6 mice were scanned twice (5 days apart). Each imaging session consisted of multifrequency OGSE and μA dMRI protocols. Metrics investigated included μA, linear diffusion kurtosis, isotropic diffusion kurtosis, and the diffusion dispersion rate (Λ), which explores the power-law frequency dependence of mean diffusivity. The dMRI metric maps were analyzed with mean region-of-interest (ROI) and whole brain voxel-wise analysis. Bland-Altman plots and coefficients of variation (CV) were used to assess the reproducibility of OGSE and μA metrics. Furthermore, we estimated sample sizes required to detect a variety of effect sizes. Results Bland-Altman plots showed negligible biases between test and retest sessions. ROI-based CVs revealed high reproducibility for most metrics (CVs < 15%). Voxel-wise CV maps revealed high reproducibility for μA (CVs ~ 10%), but low reproducibility for OGSE metrics (CVs ~ 50%). Conclusion Most of the μA dMRI metrics are reproducible in both ROI-based and voxel-wise analysis, while the OGSE dMRI metrics are only reproducible in ROI-based analysis. Given feasible sample sizes (10–15), μA metrics and OGSE metrics may provide sensitivity to subtle microstructural changes (4–8%) and moderate changes (> 6%), respectively.
49
Xu, Yanjin, Yanqing Su, Liangshun Luo, Jiangping Liu, Jingjie Guo, and Hengzhi Fu. "Study on in situ Al-Si functionally graded materials produced by traveling magnetic field." Science and Engineering of Composite Materials 19, no. 3 (September 1, 2012): 209–14. http://dx.doi.org/10.1515/secm-2011-0146.
Анотація:
AbstractThe aim of this contribution was to investigate the microstructure of in situ Al-Si functionally graded materials produced by traveling magnetic field. The research shows that the composition and associated microstructural feature of Al-Si alloys processed by this method changes from the outer of samples to the inner, respectively, from Al-Si hypereutectic with particles of primary Si to Al-Si eutectic to hypoeutectic composition with a great number of primary Al dendrites. Moreover, the hardness, the wear resistance of samples and the volume fraction of primary Si particles all have obviously gradient characteristics in the samples.
50
Gutierrez-Urrutia, Ivan, Xin Ji, Satoshi Emura, and Koichi Tsuchiya. "Microstructure-twinning relations in beta-Ti alloys." MATEC Web of Conferences 321 (2020): 12021. http://dx.doi.org/10.1051/matecconf/202032112021.
Анотація:
We have investigated twinning-microstructure relations in β-Ti alloys by statistical analysis of the evolving twin structure upon deformation by in-situ SEM testing and electron backscattering diffraction (EBSD). In particular, we have analyzed the effects of crystallographic orientation, grain size and chemical gradient structure on the nucleation and propagation behavior of {332}<113> twins in a β-Ti-15 Mo (wt.%) alloy and a multilayered β-Ti-10Mo-xFe (x: 1-3 wt.%). Microstructural parameters such as number of twins per grain and number of twins per grain boundary area were statistically analyzed.