Journal articles: 'Hardness gradient'

1

Chong, Arthur C. M., and David C. C. Lam. "Strain gradient plasticity effect in indentation hardness of polymers." Journal of Materials Research 14, no. 10 (October 1999): 4103–10. http://dx.doi.org/10.1557/jmr.1999.0554.

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Plasticity in material is typically described as a function of strain, but recent observations from torsion and indentation experiments in metals suggested that plasticity is also dependent on strain gradient. The effects of strain gradient on plastic deformation in thermosetting epoxy and polycarbonate thermoplastic were experimentally investigated by nanoindentation and atomic force microscopy in this study. Both thermosetting and thermoplastic polymers exhibited hardening as a result of imposed strain gradients. Strain gradient plasticity theory developed on the basis of a molecular kinking mechanism has predicted strain gradient hardening in polymers. Comparisons made between indentation data and theoretical predictions correlated well. This suggests that strain gradient plasticity in glassy polymers is determined by molecular kinking mechanisms.

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Lengauer, W., and K. Dreyer. "Tailoring hardness and toughness gradients in functional gradient hardmetals (FGHMs)." International Journal of Refractory Metals and Hard Materials 24, no. 1-2 (January 2006): 155–61. http://dx.doi.org/10.1016/j.ijrmhm.2005.03.008.

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KURODA, Yasunobu, Masaru KITAGAWA, Akishige SATO, Eiji KUSANO, and Akira KINBARA. "Adhesion and Hardness of Compositionally Gradient." SHINKU 41, no. 3 (1998): 111–14. http://dx.doi.org/10.3131/jvsj.41.111.

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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.

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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.

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Lam, David C. C., and Arthur C. M. Chong. "Indentation model and strain gradient plasticity law for glassy polymers." Journal of Materials Research 14, no. 9 (September 1999): 3784–88. http://dx.doi.org/10.1557/jmr.1999.0512.

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Plastic deformation of metals is generally a function of the strain. Recently, both phenomenological and dislocation-based strain gradient plasticity laws were proposed after strain gradients were experimentally found to affect the plastic deformation of the metal. A strain gradient plasticity law is developed on the basis of molecular theory of yield for glassy polymers. A strain gradient plasticity modulus with temperature and molecular dependence is proposed and related to indentation hardness. The physics of the strain gradient plasticity in glassy polymer is then discussed in relation to the modulus.

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Liang, Yi Long, Li Qiong Zhong, and Zhen Yan. "Influence of Shot Peening on the Surface Hardness of TC11 Titanium Alloy after High Cycle Fatigue Test." Materials Science Forum 849 (March 2016): 302–8. http://dx.doi.org/10.4028/www.scientific.net/msf.849.302.

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This paper studied the change of surface hardness after high-cycle fatigue (HCF) test of TC11 alloy with and without Shot Peening (WSP). The results showed that the surface hardness gradient of WSP specimens increased after R=-1 and R=0.1 HCF tests. It was found that the depth and magnitude of surface hardness gradient were related to the stress intensity and cyclic times of HCF, which increased with stress intensity; however, the surface hardness gradient of Shot Peening specimens after HCF maintained the same with that before HCF tests, the values of surface hardness varied slightly after HCF. According to analysis, the surface hardness change of WSP TC11 alloy is related to their surface integrity, which, during the cyclic loading, is due to the higher stress concentration generated on the original machining marks and the cyclic softening of surface layer generated by multi-directional stress.

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Tabushi, Kenichi, Hisashi Sato, and Yoshimi Watanabe. "Effect of Casting Condition on Density and Hardness Gradients of Al-Al₂Cu Alloy FGM Fabricated by Centrifugal In Situ Method." Materials Science Forum 631-632 (October 2009): 449–54. http://dx.doi.org/10.4028/www.scientific.net/msf.631-632.449.

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Functionally graded material (FGM) is a combined material that has a component gradient from one material at one surface to another material at the opposite surface. As one of the fabrication processes of FGM, centrifugal in-situ method has been proposed. Centrifugal in-situ method is a casting that centrifugal force is applied during solidification to both the primary crystal and the matrix. In a previous study, the density and hardness gradients of Al-3mass%Cu FGM ring fabricated by centrifugal in-situ method have been investigated. According to the study, Cu concentration within the FGM ring monolithically increases towards the ring's inner position, and its density also increases toward inner region. This is because the density of the primary -Al crystal is larger than that of the molten Al-Cu alloy in the early stage of solidification. Based on this solidification process, it is considered that the casting condition and the initial Cu concentration of Al-Cu master alloy affect on the density and hardness gradients in the Al-Cu FGM ring. In this study, effects of the casting condition on the density and hardness gradients of Al-Al2Cu FGM rings fabricated by the centrifugal in-situ method were investigated. It was found that density gradient of the Al-Al2Cu FGM rings increases with increasing Cu concentration of Al-Cu master alloys. Also, processing temperature for Al-Cu master alloy can control density gradient of Al-Al2Cu FGM rings. These phenomena were explained by variation of the densities of primary -Al and the molten Al matrix during the solidification.

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M. Adinarayanappa, Somashekara, and Suryakumar Simhambhatla. "Twin-wire welding based additive manufacturing (TWAM): manufacture of functionally gradient objects." Rapid Prototyping Journal 23, no. 5 (August 22, 2017): 858–68. http://dx.doi.org/10.1108/rpj-09-2015-0126.

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Purpose Twin-wire welding-based additive manufacturing (TWAM) is a unique process which uses gas metal arc welding (GMAW)-based twin-wire weld-deposition to create functionally gradient materials (FGMs). Presented study aims to focus on creating metallic objects with a hardness gradient using GMAW of twin-wire weld deposition setup. Design/methodology/approach By using dissimilar filler wires in twin-wire weld-deposition, it is possible to create metallic objects with varying hardness. This is made possible by individually controlling the proportion of each filler wire used. ER70S-6 and ER110S-G are the two filler wires used for the study; the former has lower hardness than the latter. In the current study, methodology and various experiments carried out to identify the suitable process parameters at a given location for a desired variation of hardness have been presented. A predictive model for obtaining the wire speed of the filler wires required for a desired value of hardness was also created. Subsequently, sample parts with gradient in various directions have been fabricated. Findings For dissimilar twin-wire weld-deposition used here, it is observed that the resultant hardness is in the volumetric proportion of the hardness of the individual filler wires. This aids the fabrication of FGMs using arc based weld-deposition with localized control of hardness, achieved through the control of the ratio of wire speeds of the individual filler wires. Four sample parts were fabricated to demonstrate the concept of realizing FGMs through TWAM. The fabricated parts showed good match with the desired hardness variation. Research limitations/implications This paper successfully presents the capability of TWAM for creating gradient metallic objects with varying hardness. Although developed using ER70S-6 and ER110S-G filler wire combination, the methodology can be extended for other filler wire combinations too for creating FGMs Originality/value GMAW-based twin-wire welding for additive manufacturing is a novel process which uses dissimilar filler wires for creating FGMs. This paper describes methodology of the same followed by illustration of parts created with bi-directional hardness gradient.

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Nikolaev Nikolov, Georgi, Anders Noel Thomsen, and Morten Kristiansen. "Hardening in laser forming under the temperature gradient mechanism." IOP Conference Series: Materials Science and Engineering 1135, no. 1 (November 1, 2021): 012006. http://dx.doi.org/10.1088/1757-899x/1135/1/012006.

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Abstract Laser forming is a contactless thermal forming process that can be applied for both single and double-curved geometries. When it comes to prototyping and small batch production, laser forming has the potential to compete with conventional sheet-metal forming processes; however, an investigation of the relationship between process parameters, hardness distribution and the bend rate is lacking. This study examines the influence of using different sets of processing parameters on the bend rate and the hardness distribution. ANSI 304 stainless steel samples of 1 and 3 mm thickness are laser formed up to 90° with a bend radius equal to their thickness. A theoretical discussion of the material’s hardening kinetics is used to generalize the results. Micro-Vickers hardness test is used to measure the hardness distribution along the 3 mm samples to support the theoretical discussion. The results show that the bend rate increases when using different sets of process parameters; furthermore, the bend arc length has shown to have a significant influence over the bend rate. An increase of hardness is observed on the bottom side of the laser formed samples, indicating potential strain hardening.

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Zhao, Na Na, Yun Hua Xu, Ke Song, Liu Liu Shen, and V. E. Ovcharenko. "Study on TaC Reinforced Iron Matrix Surface Gradient Composites Produced In Situ." Materials Science Forum 848 (March 2016): 38–42. http://dx.doi.org/10.4028/www.scientific.net/msf.848.38.

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Tantalum carbide (TaC) gradient composites were fabricated via in-situ fabrication method from the tantalum plate and gray cast iron. The morphology, phase constituents, micro-hardness, and relative abrasion resistance of the composites were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro-hardness tester and abrasive wear testing machine. The surface layer, which was ~160μm thick, was dense ceramic layer composed by ~90% submicron TaC particulates. The highest micro-hardness value of the dense ceramic layer was 13.84 GPa. In the sub-layer, the gradient distribution of TaC particulates reflected in the volume fraction decreased from 90% to 0%. While the micro-hardness value decreased from 10.81 GPa to 4.10 GPa. The metallurgical combination of the interface between the composites and matrix was perfect. The wear resistance of TaC reinforced iron matrix surface gradient composites increased significantly.

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Lee, Hun Kee, Seong Hyun Ko, and Hyun Chul Park. "On the Size Effect in Hardness by Nanoindentation Method." Key Engineering Materials 306-308 (March 2006): 911–16. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.911.

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A model describing nanoindentation as plastic deformation resulting from a strain gradient is investigated. Using a simplified axisymmetric nanoindentation, the effective strain gradient for indentation depth is derived. The proposed indentation model is a modification of Nix and Gao’s model (1998) . To validate this approach for nanoindentation, solutions for depth-dependent hardness of single various materials such as Cu, Al, Ni are compared with experiments. Results show that the proposed model agrees well with the hardness experiments.

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12

Xiu, Ziyang, Boyu Ju, Saiyue Liu, Yiwei Song, Jindan Du, Zhimin Li, Chang Zhou, Wenshu Yang, and Gaohui Wu. "Spark Plasma Sintering of AlN/Al Functionally Graded Materials." Materials 14, no. 17 (August 27, 2021): 4893. http://dx.doi.org/10.3390/ma14174893.

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In this paper, six-layer AlN/Al gradient composites were prepared by a spark plasma sintering process to study the influences of sintering temperature and holding time on the microstructure and mechanical properties. The well-bonded interface enables the composite to exhibit excellent thermal and mechanical properties. The hardness and thermal expansion properties of the composite exhibit a gradient property. The hardness increased with the volume fraction of AlN while the CTE decreased as the volume fraction of AlN. The thermal expansion reaches the lowest value of 13–14 ppm/K, and the hardness reaches the maximum value of 1.25 GPa, when the target volume fraction of AlN is 45%. The simulation results show that this gradient material can effectively reduce the thermal stress caused by the mismatch of the thermal expansion coefficient as a transmitter and receiver (T/R) module. This paper attempts to provide experimental support for the preparation of gradient Al matrix composites.

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13

Chicot, D., F. Roudet, V. Lepingle, and G. Louis. "Strain gradient plasticity to study hardness behavior of magnetite (Fe3O4) under multicyclic indentation." Journal of Materials Research 24, no. 3 (March 2009): 749–59. http://dx.doi.org/10.1557/jmr.2009.0098.

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The hardness of a material is generally affected by the indentation size effect. The strain gradient plasticity (SGP) theory is largely used to study this load dependence because it links the hardness to the intrinsic properties of the material. However, the characteristic scale-length is linked to the macrohardness, impeding any sound discussion. To find a relevant parameter, we suggest introducing a hardness length-scale factor that only depends on the shear modulus and the Burgers vector of the material and is easily calculable from the relation of the SGP theory. The variation of the hardness length-scale factor is thereafter used to discuss the hardness behavior of a magnetite crystal, the objective being to study the effect of the cumulative plasticity resulting from cyclic indentation. As a main result, the hardness length-scale factor is found to be constant by applying repeated cycles at a constant peak load whereas the macrohardness and the characteristic scale-length are both cycle dependent. When using incremental loads, the hardness length-scale factor monotonically decreases between two limits corresponding to those obtained at high and low loading rates, while the dwell-load duration increases. The physical meaning of such behavior is based on the modification of the dislocation network during the indentation process depending on the deformation rate.

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Gao, X. L. "New expanding cavity model for indentation hardness including strain-hardening and indentation size effects." Journal of Materials Research 21, no. 5 (May 1, 2006): 1317–26. http://dx.doi.org/10.1557/jmr.2006.0158.

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An expanding cavity model (ECM) for determining indentation hardness of elastic–strain-hardening plastic materials is developed. The derivation is based on a strain gradient plasticity solution for an internally pressurized thick-walled spherical shell of an elastic linear-hardening material. Closed-form formulas are provided for both conical and spherical indentations. The formulas explicitly show that indentation hardness depends on Young's modulus, yield stress, strain-hardening index, and strain gradient coefficient of the indented material as well as on the geometry of the indenter. The newly formulated ECM can capture the indentation size effect, unlike classical plasticity based ECMs. The new model reduces to existing classical plasticity based ECMs (including Johnson's ECM for elastic-perfectly plastic materials) when the strain gradient effect is not considered. The presently developed ECM is validated by comparing with existing experimental hardness data. The numerical results obtained using the new model reveal that the hardness is indeed indentation size dependent when the indentation radius is very small: the smaller the indentation, the larger the hardness. Also, the indentation hardness is seen to increase with the Young's modulus and strain-hardening level of the indented material for both conical and spherical indentations. The strain-hardening effect on the hardness is observed to be significant for materials having strong strain-hardening characteristics. In addition, it is found that the indentation hardness increases with decreasing cone angle of the conical indenter or decreasing radius of the spherical indenter. These trends agree with existing experimental observations and model predictions.

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Imai, Junji, Tadashi Hamada, Shuji Yamada, Yoshinobu Takegawa, and Hiroshi Yamada. "Development of the Hardness-gradient Blade Material by Aluminium Cladding." Materia Japan 37, no. 6 (1998): 531–33. http://dx.doi.org/10.2320/materia.37.531.

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Bign-chu, Mei, Chen Yan-lin, He Li-ping, and Yoshinari Miyamoto. "Hardness measurement of (TiB2−TiAl)/TiAl symmetrically function gradient materials." Journal of Wuhan University of Technology-Mater. Sci. Ed. 17, no. 1 (March 2002): 1–3. http://dx.doi.org/10.1007/bf02852622.

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Yang, Xiao Hong, Ni Na Zhang, Peng Xiao, and Cai Yin You. "Investigation on the Preparation and Properties of MoCu Gradient Material." Materials Science Forum 749 (March 2013): 322–27. http://dx.doi.org/10.4028/www.scientific.net/msf.749.322.

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In this study, MoCu gradient materials were prepared by the combination methods of liquid phase sintering and permeability copper. The effect of pressure and sintering temperature on the properties of MoCu gradient materials was studied. The physical and mechanical properties of MoCu20/MoCu40 and MoCu20/MoCu30/MoCu40 gradient materials were tested respectively. The results showed that the relative density of green compact and sintered gradient materials increased with the increase of pressing force from 10 tons to 30 tons. The electrical conductivity and hardness of sintered compact achieved the maximum value by the 20 tons. Within the sintering temperature range of 1100 to 1400, the relative density, electrical conductivity and hardness of sintered gradient materials increased with the increase of sintering temperature. The overall properties of sintered materials were obtained at 1350. For two-layer and three-layer MoCu gradient materials, their microstructures and chemical compositions showed a continuously and gradient change. The bending strength and the thermal conductivity of three-layer MoCu gradient materials were better than that of two-layer gradient materials.

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Meng, Qing Sen, Shao Ping Chen, Y. L. Shen, Cui Rong Liu, and Z. A. Munir. "Microstructure and Mechanical Properties of Graded Materials Prepared by Field-Activated and Pressure-Assisted Combustion Synthesis." Key Engineering Materials 368-372 (February 2008): 1876–78. http://dx.doi.org/10.4028/www.scientific.net/kem.368-372.1876.

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Using the processes of field-activated and pressure-assisted combustion synthesis (FAPACS), FGM materials (FGMs) were prepared under the conditions of field-assisted and the hot-press. The microstructure and the phase composition of the interface of the graded materials were investigated and the results showed that the metallurgical joining layer was formed in the interfaces of the (TiB2)pNi/Ni3Al/405 steel. The mechanical characterization of the gradient materials showed that the composition and the micro-hardness of the gradient material were gradient distributed, and its surface Rockwell hardness and wear resistance are better than that of hardened 20Cr steel.

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Chang, Shiun Wei, Chun Ming Chen, and Ju Liang He. "Power Modulated Plasma-Polymerized Gradient Anti-Fingerprint Transparent Protective Coating with a Gradient Composition." Advanced Materials Research 509 (April 2012): 135–37. http://dx.doi.org/10.4028/www.scientific.net/amr.509.135.

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Polymeric materials have been widely used as flexible substrates and housing parts of modern electronic wares. However, their low hardness and scratch resistance must be improved by additional protective surface coatings, which require not only mechanical durability but also additional functions such as surface hydrophobicity, oleophobicity as well as anti-fingerprint performance. To satisfy these, a power modulated plasma polymerization technique was designed to synthesize a transparent compositional gradient coating on polycarbonate (PC) substrate. Firstly, a constant flow rate of tetramethyldisiloxane (TMDSO) precursor was introduced where higher plasma power was employed to deposit a hard H-C-Si-O bottom layer. The plasma power was then decreased meanwhile admitting increased fluoromethane (CF4) gas flow as the second precursor to obtain a top layer with low surface energy. The hard bottom layer acts as a strong mechanical support and the top layer gives additional hydrophobicity and oleophobicity. Ultimately, the coating shows that a pencil hardness of 3H and Scotch-tape adhesion of 5B improves its protective function. A water contact angle of 105° and oil contact angle of 31.7° can be obtained. The coated specimen remains an optical transparency of 90% close to bare PC material. Comparing with commercialized screen protectors, the developed coating shows superior protective and anti-fingerprint performance.

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Rakhadilov, B. K., A. B. Nugumanova, P. Kowalewski, M. K. Kylyshkanov, L. B. Bayatanova, and D. N. Kakimzhanov. "Obtaining functional gradient coatings based on Al2O3 by detonation spraying." Bulletin of the Karaganda University. "Physics" Series 100, no. 4 (December 30, 2020): 22–27. http://dx.doi.org/10.31489/2020ph4/22-27.

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The article deals with the phase composition and hardness of Al2O3 coatings obtained by detonation spraying. It was found that a decrease in the delay time between shots is leading to an increase in the hardness and elastic module of Al2O3 coatings. It was found based on X-ray diffraction analysis that the main reason for the increase in hardness with a decreasing in the delay time between shots is associated with increases in the volume fraction of α- Al2O3 phase. A high content of the more ductile γ-Al2O3 phase at the substrate-coating interface leads to an increase in adhesion characteristics, and a high content of the α-Al2O3 phase on the coating surface provides high hardness and wear resistance. The studies of X-ray diffraction presented that the highest phase content is achieved when the coatings are formed with a delay time between shots of 0.25 s. It was found that increase in the volume fraction of the α-Al2O3 phase is caused by the secondary recrystallization γ → α, which occurs due to the heating of particles during coating formation, i.e. due to increase in temperature above 1100 ºС in single spots of the coating when they are put each other

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Hwang, Yeong-Maw, Yu Chen, and Sergei Alexandrov. "Manufacture of Magnesium Tubes with Gradient Hardness Distribution Using a Two-Stage Porthole Extrusion Die." Key Engineering Materials 716 (October 2016): 49–54. http://dx.doi.org/10.4028/www.scientific.net/kem.716.49.

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This paper aims to manufacture magnesium alloy tubes with gradient hardness using hot extrusion process. A two-stage porthole die together with a mandrel is designed to have a straight channel part combined with a conical part. Materials are pushed through this specially-designed die cavity to generate a non-uniform velocity distribution at cross sections between the mandrel and the die and result in different strain and strain rate distributions. Accordingly, a gradient microstructure or hardness product can be obtained. Using the finite element analysis, the effective strain distributions inside the die cavity and at the die exit are firstly discussed for various inclination angles in the conical part of the mandrel. Then, hot extrusion experiments with a two stage porthole die set are conducted to obtain magnesium alloy products with gradient microstructures and hardness. Using a die set of mandrel inclination angle of 10o and die inclination angle of 25o, gradient microstructures of grain sizes of 4.30μm, 5.92 μm and 3.67μm at the outer surface, center zone, and inner surface, respectively, are achieved.

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Gerberich, W. W., N. I. Tymiak, J. C. Grunlan, M. F. Horstemeyer, and M. I. Baskes. "Interpretations of Indentation Size Effects." Journal of Applied Mechanics 69, no. 4 (June 20, 2002): 433–42. http://dx.doi.org/10.1115/1.1469004.

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For very shallow indentations in W, Al, Au, and Fe-3wt%Si single crystals, hardness decreased with increasing depth irrespective of increasing or decreasing strain gradients. As such, strain gradient theory appears insufficient to explain the indentation size effect (ISE) at depths less than several hundred nanometers. Present research links the ISE to a ratio between the energy of newly created surface and plastic strain energy dissipation. Also, the contact surface to plastic volume ratio was nearly constant for a range of shallow depths. Based on the above, an analytical model of hardness versus depth provides a satisfactory fit to the experimental data and correlates well with embedded atom simulations.

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Cabibbo, Marcello, Alessandra Fava, Roberto Montanari, Ekaterina Pakhomova, Chiara Paoletti, Maria Richetta, and Alessandra Varone. "Grain Orientation and Hardness in the Graded Interlayer of Plasma Sprayed W on CuCrZr." Applied Sciences 12, no. 4 (February 10, 2022): 1822. http://dx.doi.org/10.3390/app12041822.

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In this work a W coating was deposited through PS in Ar-H2 atmosphere on a substrate of CuCrZr with an interlayer consisting of gradually changing fractions of Cu and W. The W coating and the interlayer showed good adhesion and no cracks were observed. The hardness of W and Cu along the interlayer was determined by nano-indentation tests and the results showed that a hardness gradient does exist in both the metals. Microstructural examinations suggest that the hardness gradient depends on the texture, which exhibits significant differences along the interlayer: multiplication and movement of dislocations, and localized plasticity under the indenting tip are strongly affected by grain orientation.

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Golombieski, Jaqueline Ineu, Alessandra Janaína Becker, Caroline Bruzza Almeida, Ana Paula Gottlieb Almeida, and Bernardo Baldisserotto. "Preference behavior of silver catfish, Rhamdia quelen, juveniles in waters with pH gradients: laboratory experiments." Neotropical Ichthyology 11, no. 3 (September 2013): 661–65. http://dx.doi.org/10.1590/s1679-62252013000300019.

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The aim of this study was to determine the preferred pH in silver catfish Rhamdia quelenjuveniles acclimated to different water hardness and the effect of shelters and infection by Ichthyophthirius multifiliis. Fish were acclimated for two weeks at different water hardness levels (4, 24, 50, or 100 mg CaCO3 L-1) and then transferred to a polyethylene tube with a pH gradient ranging from 3.5 to 11.7 and maintaining the same hardness. The position of the fish in the pH gradient was observed at 1, 2, 4, 6, 8, 10, and 12 h after transfer. Acclimation to different water hardness did not change pH preference of uninfected silver catfish (pH 7.30-7.83), and the presence of a shelter at the preferred pH or outside this preferred pH did not change the chosen pH range, either. Consequently silver catfish favored the acid-base regulation over shelter seeking tendency. Juveniles infected with I. multifiliis acclimated to water hardness of 24 mg CaCO3 L-1 preferred alkaline pH (9.08-9.79). This choice is not explained by the higher Na+ levels at alkaline pH compared to neutral pH because infected and uninfected fish choose the same waterborne Na+ levels in a Na+ gradient with the same pH.

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Zang, Wan Hong, Chang Lun Yuan, and Yan Li. "Al₂O₃-TiC/Fe Functionally Gradient Material Prepared by SHS Casting." Materials Science Forum 704-705 (December 2011): 6–10. http://dx.doi.org/10.4028/www.scientific.net/msf.704-705.6.

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Al2O3-TiC particles reinforced iron matrix functionally gradient material is successfully fabricated by combining the methods of self-propagating high-temperature synthesis (SHS) with casting. The SHS products are analyzed by SEM and XRD and EDS. The results show that the grain size of the particle is round 1μm~3μm, the composition of the Al2O3-TiC/ Fe surface composite takes on a gradient distribution from outside to inside, and transforms gradually to the matrix metal. The hardness below 0.5mm from exterior surface of the functionally gradient materials increases dramatically and gradually changes to the hardness of the matrix. Key words: In situ generation; SHS; Casting; Surface composite material; FGM

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Fauser, Heidi, Christophe Poizat, Markus Grimm, Heiko Knoll, Winfried Schmitt, and Renate Freudenberger. "Electrodeposition of Gradient Layers for Improved Impact Load Resistance." Materials Science Forum 492-493 (August 2005): 53–58. http://dx.doi.org/10.4028/www.scientific.net/msf.492-493.53.

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The aim of the research project described here is to increase the durability of components under cavitation erosion by electrodeposition of gradient layers. Parallel to the material development, a simulation tool is elaborated to determine the optimal gradient layers for improved load resistance. This helps in minimising the number of prototype layer systems to be manufactured within the project. The initial experiments were executed with the nickel-phosphorus system, which is well-known for its favourable properties regarding hardness, corrosion resistance and tribology. Single and gradient layers are characterised and evaluated in view of the following properties: hardness, internal stresses, ductility, coefficient of friction, wear resistance, elastic modulus and tensile strength.

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Yang, Li, Ying Huai Qiang, Fu Shan Chen, Yang Gao, and Yun Tian Zhong. "Effect of Working Current on Microstructure and Properties of Cylinder Hardened by Plasma Beam at Junction of the Hardening Traces." Advanced Materials Research 314-316 (August 2011): 98–101. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.98.

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To improve wear resistance and service life of boron cast iron cylinder, plasma beam hardening on surface is adopted.Scanning electron microscope,X-ray diffractometer and micro-hardness tester is used to analyze the effect of working current on the structure and properties of plasma beam hardening layer at the junction of the hardening traces. The results show that the microstructure of hardening layer at the junction is hidden acicular martensite, retained austenite and flake graphite. With the increase of working current, the content of retained austenite decreases, the hardness and depth of the hardening layer increases. The highest hardness is not achieved at the surface of hardening layer but at the second-surface layer which has a certain distance to the surface. The uneven distribution of hardness in hardening layer leads to large gradient at the both sides of the highest hardness and the gradient decreases with the increase of working current.

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Agustsson, R., P. Carriere, O. Chimalpopoca, V. А. Dolgashev, M. A. Gusarova, S. V. Kutsaev, and A. Yu Smirnov. "Experimental studies of a high-gradient X-band welded hard-copper split accelerating structure." Journal of Physics D: Applied Physics 55, no. 14 (January 5, 2022): 145001. http://dx.doi.org/10.1088/1361-6463/ac4632.

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Abstract Recent research on high-gradient radio frequency (RF) accelerating structures indicates that the use of hard copper alloys provides improvement in high gradient performance over annealed copper. Such structures are made by bonding individually manufactured parts. However, there are no well-established bonding techniques that preserve the hardness, surface finish and cleanliness required for high gradient operation. To preserve the copper hardness, RadiaBeam has developed a novel high-gradient split accelerating structure, based on electron beam welding joining technique. This technique provides efficient bonding with strong, clean welds and minimal thermal loading, while maintaining a clean inner RF environment. Our RF design and fabrication methodology limits the small heat affected zone to the outer cavity envelop, with virtually no distortions or thermal loading of critical RF surfaces. It also incorporates provisions to precisely control the gap despite conventional issues with weld joint shrinkage. To date we have manufactured and validated an RF accelerating structure joined by electron-beam welding that incorporates a novel open split design to significantly reduce the assembly complexity and cost. In this paper, we will present the electromagnetic design of this structure, discuss bonding, and present the results of high-power tests, where the accelerating gradients of 140 MV m−1 with surface peak fields of 400 MV m−1 were achieved for flat-top pulse length of 600 ns with an RF breakdown rate of 10−4 1/(pulseċm).

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Elkotb, Hazem H., Rania Mostafa, A. A. Abdel Samad, and Tawakol A. Enab. "Manufacturing and Characterization of Functionally Graded Material Automotive Piston Using Centrifugal Casting Technique." Solid State Phenomena 318 (May 2021): 13–24. http://dx.doi.org/10.4028/www.scientific.net/ssp.318.13.

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The process of fabricating reliable materials according to efficient usage has become one of the most vital concerns. In this paper, the fabrication of functionally graded materials (FGMs) is the target using a specified application of an internal combustion engine piston model to achieve such a gradient. With a convenient rotational speed under the concept of centrifugal casting technique, the required gradient piston was successfully produced from two pure aluminum alloys A336 and A242 by such a new mechanical technique for having the required gradient. The percentages of internal ingredients, mainly, silicon were controlled axially through the piston. Chemical composition analysis, micro-hardness and wear resistance tests were performed to check the gradient and to know the difference between mechanical properties for each piston portion from its top combustion chamber to its skirt, achieving compatible results through performed tests. Obvious opposite direction gradient of silicon content to copper content appeared. Micro-hardness, wear resistance and coefficient of friction values showed a successfully gradient in the axial direction of the piston model.

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Wang, W., and K. Lu. "Nanoindentation measurement of hardness and modulus anisotropy in Ni3Al single crystals." Journal of Materials Research 17, no. 9 (September 2002): 2314–20. http://dx.doi.org/10.1557/jmr.2002.0339.

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Hardness and elastic modulus of (111), (110), and (001) oriented Ni3Al single crystals were determined by nanoindenter measurements. Obvious elastic modulus anisotropy and hardness anisotropy were observed. The modulus for (001) was about 17% smaller than that for (111), (110). The hardness was found to be strongly dependent on the indentation size and exhibited a small anisotropy at low indentation loads. When the indentation load was increased further, the hardness anisotropy became apparent. The hardness for (111) was observed to be higher compared to (001). The indentation hardness size effect was examined by using strain gradient plasticity theory.

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Kolaklieva, Lilyana, Roumen Kakanakov, D. Chaliampalias, G. Vourlias, T. Cholakova, Ch Pashinski, V. Chitanov, Ch Bahchedjiev, N. Petkov, and Efstathios K. Polychroniadis. "Mechanical, Structural and Thermal Properties of Multilayered Gradient Nanocomposite Coatings." Journal of Nano Research 17 (February 2012): 193–202. http://dx.doi.org/10.4028/www.scientific.net/jnanor.17.193.

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Multilayered, Gradient Tialsin-Based Nanocomposite Coatings Have Been Developed and Investigated with Respect to their Applicability in the Machining Industry. the Main Coating Layer Was Composed of 5-8 Nm Tin and Aln Nanograins. the Coating Possessed Hardness as High as 40 GPA, which Allows it to Be Classified as Superhard. during Heating up to 900oC in Air in Steps of 100oC for 6 H at each Temperature, the Coating Showed Good Stability up to 700oC. Thermal Treatment over this Temperature Caused a Decrease in the Hardness to Values Characteristic for Tialn Multilayered Coatings, while the Adhesion to the Substrate Remained Steady.

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Zhou, Luohui, Jingling Lan, Jili Liu, Xu Li, Bowen Shi, and Shuyang Zheng. "Effect of Gradient Heat Treatment on Microstructure and Properties of Cu–Al–Mn Shape Memory Alloy." Materials 12, no. 16 (August 7, 2019): 2505. http://dx.doi.org/10.3390/ma12162505.

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The columnar-grained Cu–Al–Mn shape memory alloys (SMAs), which have good shape memory properties and are prepared by a unidirectional solidification technique, were subjected to a gradient heat treatment under temperatures ranging from 100 to 450 °C. After this treatment, the microstructure, hardness, transformation temperature and shape memory properties of these samples could exhibit gradient changing trends, all of which were investigated by optical microscope, scanning electron microscopy (SEM), a Vickers microhardness tester, and a compression machine. The microstructure observation result shows that the acicular bainite-precipitated phase produces from scratch and then grows continuously with the increasing of the heat treatment temperature, finally presenting a graded distribution from one end section to another of the sample. The hardness tests give the samples results also increasing with temperature. Specifically, the change relationship between hardness and the treatment temperature mathematically satisfies dynamic function. In addition, it can be concluded from mechanical tests the compressive elastic–superelastic strain and strength of the samples show gradient variation features. Overall, our experimental investigation indicates that a gradient heat treatment is an effective way to conduct microstructure control or design for the Cu–Al–Mn SMAs, and their graded properties are mainly caused by the different fractions of the bainite phase producing in different local areas after the gradient heat treatment.

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Wang, Wei, Huaiju Liu, Caichao Zhu, Jinyuan Tang, and Chenxu Jiang. "Evaluation of contact fatigue risk of a carburized gear considering gradients of mechanical properties." Friction 8, no. 6 (December 4, 2019): 1039–50. http://dx.doi.org/10.1007/s40544-019-0317-z.

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AbstractCarburized gears are widely used in geared machines such as wind turbines. Contact fatigue problems occur in engineering practice, reducing reliabilities of machines. Contact fatigue failures are related to many factors, such as gradients of mechanical properties of the hardening layer. In this work, an elastic-plastic contact model of a carburized gear is developed based on the finite element method to evaluate contact fatigue failure risk, considering variations in hardness and strength. The Dang Van multiaxial equivalent stress is calculated via Python coding within the Abaqus framework. The gradient of yield strength along the depth from case to core is considered. The concept of local material fatigue failure risk is defined to evaluate the probability of pitting failure. The effects of design factors, such as the case hardening depth (CHD), surface hardness, and contact pressure on fatigue failure risk, are studied. As the CHD increases or the surface hardness decreases, the risk of deep spalling failure reduces. The increase in surface hardness leads to a decreased risk of pitting failure, while the variation in CHD hardly affects the pitting failure risk.

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Qian, Linmao, Hui Yang, Minhao Zhu, and Zhongrong Zhou. "Experimental Verification of the Strain-Gradient Plasticity Model for Indentation." Journal of Materials Research 20, no. 11 (November 2005): 3150–56. http://dx.doi.org/10.1557/jmr.2005.0395.

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The indentation size effect of pure iron samples with various pre-plastic tensile strains has been experimentally investigated and analyzed. With the increase in the strain, the indentation size effect of iron samples becomes weak, accompanied by the multiplication of the statistically stored dislocations. All of the hardness (H) versus indentation depth (h) curves fit the strain-gradient plasticity model for indentation of Nix and Gao well. Two fitting parameters, the hardness in the limit of infinite depth (H0) and the characteristic length (h*), were obtained for each curve. The hardness (H0) of iron samples can also be estimated as the microhardness (H) at a very large depth, h ≅ 10h*. Both the fitted H0 and the measured H0′ increase linearly with the tensile yield stress σy of iron samples, indicating a dependence of H0 on the statistically stored dislocation density through σy. Furthermore, 1/√h* shows a linear increase with the tensile yield stress σy, which also agrees qualitatively with the general prediction of the Nix and Gao theory. Therefore, our experiments and analysis demonstrate that the strain-gradient plasticity model for indentation of Nix and Gao can interpret the indentation size effect with satisfied precision.

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Huang, Bin, Ya Zheng Liu, Le Yu Zhou, Guo Wei Li, and Dan Zhang. "Research on Fatigue Fracture Defect of 23CrNi3Mo Drill Steel." Advanced Materials Research 314-316 (August 2011): 1955–59. http://dx.doi.org/10.4028/www.scientific.net/amr.314-316.1955.

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In order to analyze the key factor to affect fatigue life of drill tools, fracture morphology and microstructure of defect samples made of 23CrNi3Mo with different types was observed by optical microscope and scanning electron microscope(SEM), and micro-hardness was tested, then failure reason was analyzed. The results show that the plastic deformation features of defect sample with high fatigue life is obvious during fatigue cracks generation and expanding, which has good ability to resist fatigue crack propagation, while impacter drill defect sample appears brittle fracture features. The surface of Atlas and impacter drill both have carburized layer with high hardness. The wide transitive layer of Atlas drill renders the strength of carburized layer and the roughness of matrix well matched and has well hardness gradient, while the impacter doesn’t. Thus the hardness gradient and the matching of strength and toughness affect the drill fatigue life heavily, and carburization and heat treatment process are very important.

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Ren, Zhi Lan, and Xin Heng Wang. "Effect of High-Energy Shot-Peening on H13 Tool Steel Ion-Nitriding." Advanced Materials Research 393-395 (November 2011): 67–71. http://dx.doi.org/10.4028/www.scientific.net/amr.393-395.67.

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High-energy shot-peening on H13 steel after quenched. The samples with or without high-energy shot-peening were ion-nitrided at 520°C for 3h．The Microstructure，nitriding depth, hardness gradient, surface phase and Corrosion resistance of the nitride layers were compared between the high-energy shot-peening samples and the original samples using optical microscope, micro-hardness tester, X-ray diffraction and CH1660A electrochemical test. Results show that the high-energy shot-peening greatly speeds up the nitriding on the H13 steel at 520°C for 3h.. The depth of ion-nitriding layer after shot peening is from 0.11mm to 0.16mm, micro-hardness of the surface layer is from 998HV0.5 to 1105HV0.5, The hardness gradient is slightly flat . Phase structure and content of the surface is different by Powerful shot-peening and not. Corrosion resistance of the samples by high-energy shot-peening is significantly improved because it is easier to form a stable passive film.

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Xue, Z., Y. Huang, K. C. Hwang, and M. Li. "The Influence of Indenter Tip Radius on the Micro-Indentation Hardness." Journal of Engineering Materials and Technology 124, no. 3 (June 10, 2002): 371–79. http://dx.doi.org/10.1115/1.1480409.

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The micro-indentation experiments have shown that the indentation hardness depends not only on the indentation depth but also on the indenter tip radius. In fact, the indentation hardness displays opposite dependence on the indentation depth h for a sharp, conical indenter and for a spherical indenter, decreasing and increasing, respectively, with increasing h. We have developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of indenter tip radius. The same indentation model captures this opposite depth dependence of indentation hardness, and shows the opposite depth dependence resulting from the different distributions of strain and strain gradient underneath a conical indenter and a spherical indenter. We have also used the finite element method to study the indentation hardness for a spherical indenter as well as for a conical indenter with a spherical tip. It is established that the effect of indenter tip radius disappears once the contact radius exceeds one half of the indenter tip radius.

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Yang, Shaopeng, Peifeng Cheng, Fangzhong Hu, Wenchao Yu, Chi Zhang, Kaizhong Wang, and Maoqiu Wang. "Very High Cycle Fatigue Properties of 18CrNiMo7-6 Carburized Steel with Gradient Hardness Distribution." Coatings 11, no. 12 (December 2, 2021): 1482. http://dx.doi.org/10.3390/coatings11121482.

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As research of the high cycle fatigue of carburized gear steel could not meet the status quo of longer and longer service lives, research of very high cycle fatigue (VHCF) performance has become the focus of current research. The VHCF properties of case-hardening steel 18CrNiMo7-6 after being carburized with gradient hardness distribution were investigated by means of ultrasonic fatigue tests. The results showed that the carburized specimens with a case hardness of 705 HV and core hardness of 530 HV showed VHCF phenomenon, and the fatigue lives continuously increased to even 109 cycles as the stress amplitude decreased to about 500 MPa. Observations of the fracture surfaces of the fatigue specimens showed that the fatigue crack initiation sites were located in the transition area with the hardness at about 580 HV. It was found that the transition area had low VHCF properties, since the core did not show VHCF phenomenon, and the case had a higher hardness. A fine microstructure was observed in the granular bright facet (GBF) area, and the stress intensity factor ΔKGBF was measured to be 3.04 MPam−1/2. The 109 cycles fatigue life was predicted based on the inclusion size, and the 1010 cycles fatigue life was 490 MPa based on the prediction model.

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Li, Chenchen, Xuefeng Yang, Shouren Wang, Yanjun Wang, and Jinlong Cao. "Preparation of WC Reinforced Co-Based Alloy Gradient Coatings on a H13 Mold Steel Substrate by Laser Cladding." Coatings 10, no. 2 (February 14, 2020): 176. http://dx.doi.org/10.3390/coatings10020176.

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H13 die steel often fails as a result of physical and chemical effects such as wear, erosion and cyclic stress. Accordingly, the study evaluates Co-based gradient coating on an H13 steel featuring a stress-relieving effect. Scanning electron microscope and X-ray diffraction were used to analyze the microstructure and phase of the coatings. A microhardness tester and friction and wear tester were used to compare the hardness and wear resistance of the coatings and the substrate, and the wear morphology was observed. A pendulum impact test was used to compare the impact resistance of the coatings and the substrate, and the fracture morphology was observed. Finally, a corrosion test was used to compare the corrosion resistance of coatings and substrate. The results show that the Co-based gradient coatings have good combinations with the substrate, the hard phase content gradually increases from the bottom to the top of the coating, and the crystal microstructure generally maintains a distribution trend from coarse to fine. The hardness of the gradient coatings is significantly higher than the substrate, and from the coating surface to the substrate, the hardness decreases slowly. The wear loss of the coatings is much lower than that of the substrate, the main wear mechanism of the substrate is abrasive wear, and the main wear mechanism of the coatings is brittle spalling. While the gradient coatings increase the surface hardness, the brittleness also increases, the impact resistance of the coatings is lower than that of the substrate, the fracture form of the substrate is a ductile fracture, and the fracture form of the coating is a brittle fracture. The gradient coatings effectively improve the corrosion resistance of the substrate surface, and the higher the content of the reinforcing phase, the better the corrosion resistance of the coatings.

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Ratajski, Jerzy, Adam Gilewicz, Katarzyna Mydłowska, and Łukasz Szparaga. "Inter-Relationship between Coating Micro/Nanostructure and the Tribological Performance of Zr–C Gradient Coatings." Coatings 10, no. 11 (November 20, 2020): 1121. http://dx.doi.org/10.3390/coatings10111121.

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The research presented in this article concerns Zr–C gradient coatings that were deposited on HS6-5-2 steel by reactive magnetron sputtering from the Zr target in appropriately programmed C2H2 mass flow rate, resulting in various profiles of atomic carbon concentrations in the coating and consequently in spatial change of the properties (H, E, …) and behavior (H/E, H3/E2, We). In particular, the characteristic changes in hardness and Young’s modulus in the Zr–C coatings represented approximately by the bell curve, which has a maximum at the content of about 50 at.% C, were an inspiration to study the behavior of gradient coatings with carbon content in the range of 0–50 and 50–85 at.% with the same hardness change profile. The obtained results indicate that, firstly, the gradient of spatial changes in the coating composition increases their resistance to cohesive damage in comparison to non-gradient coatings, and, secondly, the results show that high hardness is a desired property but not sufficient to ensure adequate coating performance. Independently, an appropriate nano/microstructural structure is necessary, which determines their tribological behavior. In particular, in the case of the tested Zr–C coatings, the obtained results indicate that gradient coatings with a carbon content in the range of 50–85 at.% have better properties, characterized by the critical force Lc2, wear, coefficient of friction, H/E and H3/E2 ratios.

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Anikeev, Andrey N., Ilia V. Chumanov, and Vadim Sedukhin. "Studying the Effect of Fine Particles of Tungsten Carbide on the Macro-Structure, Hardness and Microhardness of Gradient Steel Billets." Materials Science Forum 986 (April 2020): 3–8. http://dx.doi.org/10.4028/www.scientific.net/msf.986.3.

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Creating a gradient of properties in a single material is challenging for scientists and engineers. For this purpose, such methods are used as: welding of steels of different chemical compositions, joint rolling of steel sheets, sealing and surfacing of various kinds. All of these methods have a big disadvantage: under load, the material is destroyed in the weakest place - the place where the layers join. In this article, the authors proposed to obtain a gradient of properties in steel castings due to the introduction of dispersed particles of tungsten carbide into the crystallizing melt during centrifugal casting. The particles introduced serve as crystallization centers, accelerate the crystallization process and increase certain types of mechanical properties (hardness, microhardness, tensile strength). In addition, the particles of tungsten carbide have high hardness; therefore, in the structure of the workpieces they serve as reinforcing elements that strengthen the structure. The uneven distribution of particles in the preform being formed is possible for two reasons: tungsten carbide has a density greater than the melt, and besides, centrifugal force acts on them. The article describes the experiment and its results on the production of metal preforms with a gradient of properties. The introduced particles significantly influenced the macro-structure of the prepared castings. The article also presents the results of a study of the effect of particles on the hardness and micro-hardness of the resulting blanks.

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42

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.

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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.

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Wang, Qing Feng, Cheng Jia Shang, Ya Nan Wang, and Wayne Chen. "Microstructure and Mechanical Properties of Simulated Heat Affected Zone of an Ultrafine Grain Steel Laser Weld." Key Engineering Materials 353-358 (September 2007): 2021–24. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.2021.

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In this paper, the very rapid thermal cycles imposed on an ultrafine grain steel plate were successfully simulated using a Gleeble™ simulator. The simulated heat affected zone was obtained suitable for Vickers hardness and impact toughness examination of laser weld that originally bear a narrow zone with high hardness gradient. Effect of preheat treatment on the mechanical behavior of laser HAZ was estimated. It was indicated that the simulated HAZ was composed of fine martensitic ferrite laths with average width in 65nm and 175nm in the case of preheat at 200°C and not, respectively. The laths were cramped by retained austenite film within the prior austenite grain with average size of 9.5 and 6.5μm, much less than that of base metal. The impact toughness of HAZ was improved by laser thermal cycle comparing to that of base metal, and there is no obvious brittle-ductile transition under temperatures from -80°C to 20°C. Preheat treatment of steel plate prior to laser welding resulted in an effective reduction of the maximum hardness and alleviation of the hardness gradient in the weld.

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Wang, Gui Tang, Jian Lin Zhu, Pei Liang Cao, and Wen Juan Liu. "Research on Vickers Hardness Image Definition Evaluation Function." Advanced Materials Research 129-131 (August 2010): 134–38. http://dx.doi.org/10.4028/www.scientific.net/amr.129-131.134.

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A definition evaluation function is proposed for the Vickers hardness indentation images in this paper. Based on the characteristics of Vickers hardness indentation image, we choose the gradient function as definition evaluation criteria for the image. Because of the advantage of Brenner evaluation function and the image features itself, this paper puts forward a new evaluation function at the idea of Brenner evaluation function, that is not only more suitable for evaluating the Vickers hardness indentation image than Brenner function, but also having the merit of it and becoming more practical according to the experiments.

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Zhou, Rong, Lu Li, Ye Hua Jiang, Rong Feng Zhou, and Jia Wang. "Hypereutectic Al-Si Alloy Tube with Gradient Structure Produced by Rheo-Squeeze Casting." Solid State Phenomena 217-218 (September 2014): 461–67. http://dx.doi.org/10.4028/www.scientific.net/ssp.217-218.461.

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In this paper, the wear property of a rheo-squeeze casting Al-22Si-2Fe-1.4Mn alloy tube was investigated. The semi-solid slurry of Al-22Si-2Fe-1.4Mn alloy was prepared using segmented cooling plates. The results showed that the volume fraction and equivalent diameter of the hard particles (primary silicon and blocky Fe-rich phases) increased gradually from the outside to the inside of the tube wall. The microstructures of the tube were examined with an optical microscope, scanning electron microscope, X-ray diffraction. The micro-hardness of hard particles and the macro-hardness from the outside to the inside of the wall were tested, respectively. Wear resistance tests of the outside and the inside of the wall showed wear resistance, which depends on the distribution and the volume fraction of the hard particles, increased gradually from the outside to the inside of the tube wall, changed in gradient and agreeing with the distribution law of macro-hardness.

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Makarov, A. M., T. I. Bobkova, A. F. Vasiliev, D. A. Geraschenkov, I. S. Prudnikov, and B. V. Farmakovsky. "Effect of gas phase composition on functional-gradient coatings formation by supersonic cold gas dynamic spraying." Voprosy Materialovedeniya, no. 1(93) (January 6, 2019): 65–69. http://dx.doi.org/10.22349/1994-6716-2018-93-1-65-69.

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The paper develops method for manufacturing wear and corrosion-resistant gradient coating. A special feature of the proposed method is the creation of chemical composition gradient due to controlled variation of the gas phase composition when applying supersonic cold gas-dynamic spraying. This ensures high adhesive strength of the composite coatings of the metal-non-metal system in combination with high micro-hardness of the peripheral layers. Such functional gradient coatings have wide practical applications.

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Jo, Yeong-Kwan, Yeong-Wook Gil, Do-Sik Shim, Young-Sik Pyun, and Sang-Hu Park. "Control of Local Hardness Gradient of Metal Surface by Inclined Surface Treatment Using Ultrasonic Nanocrystal Surface Modification." International Journal of Precision Engineering and Manufacturing-Green Technology 8, no. 2 (January 13, 2021): 533–46. http://dx.doi.org/10.1007/s40684-020-00303-6.

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AbstractWe propose an effective method to control the local hardness and morphology of a metal surface by tilting the incident angle of a horn during ultrasonic nanocrystal surface modification (UNSM). In this study, surface treatment using UNSM was performed on an S45C specimen and a parameter study was conducted for optimization. The process parameters were the feeding rate, static load, striking force, and processing angle (Ф). In particular, the Ф was analyzed by tilting the horn by 0°, 10°, 20°, 30°, 40°, and 45° to understand its effect on surface hardness and changes in the morphology. From fundamental experiments, some important phenomena were observed, such as grain-microstructure changes along the processing and thickness directions. Furthermore, to verify the practical usefulness of this study, a flat and a hemispherical specimen of S45C material were treated using UNSM with various values of Ф. A significant change in hardness (an increase from 2–45%) and a gradual hardness gradient on the tested specimens could be easily realized by the proposed method. Therefore, we believe that the method is effective for controlling the mechanical hardness of a metal surface.

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48

Huang, Y., Z. Xue, H. Gao, W. D. Nix, and Z. C. Xia. "A Study of Microindentation Hardness Tests by Mechanism-based Strain Gradient Plasticity." Journal of Materials Research 15, no. 8 (August 2000): 1786–96. http://dx.doi.org/10.1557/jmr.2000.0258.

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We recently proposed a theory of mechanism-based strain gradient (MSG) plasticity to account for the size dependence of plastic deformation at micron- and submicronlength scales. The MSG plasticity theory connects micron-scale plasticity to dislocation theories via a multiscale, hierarchical framework linking Taylor's dislocation hardening model to strain gradient plasticity. Here we show that the theory of MSG plasticity, when used to study micro-indentation, indeed reproduces the linear dependence observed in experiments, thus providing an important self-consistent check of the theory. The effects of pileup, sink-in, and the radius of indenter tip have been taken into account in the indentation model. In accomplishing this objective, we have generalized the MSG plasticity theory to include the elastic deformation in the hierarchical framework.

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Bruder, Enrico, Tilman Bohn, and Clemens Müller. "Properties of UFG HSLA Steel Profiles Produced by Linear Flow Splitting." Materials Science Forum 584-586 (June 2008): 661–66. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.661.

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Linear flow splitting is a new cold forming process for the production of branched sheet metal structures. It induces severe plastic strain in the processing zone which results in the formation of an UFG microstructure and an increase in hardness and strength in the flanges. Inbuilt deformation gradients in the processing zone lead to steep gradients in the microstructure and mechanical properties. In the present paper the gradients in the UFG microstructure and the mechanical properties of a HSLA steel (ZStE 500) processed by linear flow splitting are presented, as well as a calculation of local strength from hardness measurements on the basis of the Ludwikequation. In order to investigate the thermal stability of the UFG microstructure heat treatments below the recrystallization temperature were chosen. The coarsening process and the development of the low angle to high angle grain boundary ratio in the gradient UFG microstructure were monitored by EBSD measurements. It is shown that heat treatment can lead to a grain refinement due to a strong fragmentation of elongated grains while only little coarsening in the transverse direction occurs. A smoothing of the gradients in the UFG microstructure as well as in the mechanical properties is observed.

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Cholakova, T., V. Chitanov, D. Chaliampalias, Lilyana Kolaklieva, R. Kakanakov, Ch Bahchedjiev, N. Petkov, et al. "Study of the Structural and Mechanical Properties of Nanocrystalline TiAlSiN Gradient Coatings." Journal of Nano Research 27 (March 2014): 15–24. http://dx.doi.org/10.4028/www.scientific.net/jnanor.27.15.

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A study of the structural and mechanical properties of nanocrystalline TiAlSiN gradient coatings deposited by cathodic arc deposition techniques at 500 °C and post-annealed at 525 °C is presented. Analysis of the coatings, chemical composition and microstructure revealed that the coatings have a structure based on (Ti, Al)N nanocrystals with an average size of 10 nm embedded in an amorphous Si3N4 phase. The study of the mechanical properties showed that post-annealing causes improvement and increase of the coatings hardness. A maximum hardness of 48 GPa and elastic modulus of 560 GPa were measured. Also, excellent adhesion to the WC-Co substrate was observed in the post-annealed coatings.

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Journal articles on the topic 'Hardness gradient'

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