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Academic literature on the topic 'L12 ordered precipitates'

Author: Grafiati
Published: 6 September 2023

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Journal articles on the topic "L12 ordered precipitates"

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Sun, Yuanyang, Yuhong Zhao, Huijun Guo, Xiaolin Tian, and Hua Hou. "Early Stages of Precipitation in γ' Phase of a Ni–Al–Ti Model Alloy: Phase-Field and First-Principles Study." Science of Advanced Materials 12, no. 5 (May 1, 2020): 746–54. http://dx.doi.org/10.1166/sam.2020.3716.

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The early stages of precipitation process of the γ' phase of a Ni–Al–Ti alloy are investigated by microscopic phase-field and first-principles calculations. The simulated results indicate that a pre-precipitate with L10 structure appears before the L12 ordered phase, and then this metastable phase gradually transforms to L12 ordered phase; finally, the precipitated phase is composed of γ' ordered phase and γ matrix phase. The occupation probabilities of Al, Ni, and Ti atoms also illustrate the formation of the L10 phase and its situ conversion to L12 ordered phase constituted by a complicated compound Ni3(AlTi). Through the analyses of order parameter and occupation probability, the precipitation mechanism of γ' phase is drawn as a combination of congruent ordering and destabilization decomposition. Meanwhile, we also find that the growth and coarsening of the γ' phase occur via mixed mechanisms of Ostwald ripening and coalescence coarsening of neighboring precipitates. Moreover, the first-principles method is applied to calculate the thermodynamic parameters and validate further the appearance of the metastable phase and the site preference of Ti atom, which offers an explanation for atomic occupancy characteristics in the precipitate.
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Doi, Minoru. "Two-Phase Microstructures Formed by Phase-Separation of Coherent Precipitates in Elastically Constrained Alloy Systems." Materials Science Forum 638-642 (January 2010): 2215–20. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.2215.

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Coherent two-phase microstructures consisting of ordered precipitate and disordered matrix phases sometimes exhibit a phase-separation, which brings the split and/or the decelerated coarsening of precipitates. When the coherent two-phase microstructure of A1+L12 (+’) in Ni-base alloys are aged inside the two-phase region of A1+L12 , the L12 precipitate sometimes exhibit a phase-separation and A1 phase newly appears and grows in each L12 precipitate. Phase-separations of the same type to the above also take place due to ageing of coherent two-phase microstructures of A2+D03 and A2+B2 in Fe-base alloys: D03 and B2 precipitates sometimes exhibit phase-separations and A2 phase newly appears and grows in both precipitates. These types of phase-separation take place under the influence of chemical free energy. In the course of further ageing, the new disordered phases of A1 and A2 change their morphology in various ways depending on the elastic constraint: i.e. the morphology of new A1 or A2 phase is influenced by the elastic energies and the surface energy.
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Zhao, Bing Bing, Xian Ping Dong, Feng Sun, and Lan Ting Zhang. "Impact of L12-Ordered Precipitation on the Strength of Alumina-Forming Austenitic Heat-Resistant Steels." Materials Science Forum 941 (December 2018): 692–97. http://dx.doi.org/10.4028/www.scientific.net/msf.941.692.

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Alumina-forming austenitic (AFA) heat-resistance steels firstly developed by Yamamoto et al. at Oak Ridge National Laboratory have been reported as a new promising class of steels with potential for use in high temperature applications in recent years. The creep resistance of AFA steels is improved mainly by precipitation strengthening. Besides modifying the typical existing precipitates, i.e. MC and M23C6 type carbides, B2-NiAl and Fe2Nb-type Laves phase, introduction of coherent L12-ordered precipitate is highly desired. L12-ordered phase gamma prime (γ’) is the most important precipitate for high-temperature strengthening in Ni-based superalloys. In the present work, we demonstrate that addition of 2.8 wt. % Cu to an AFA steel promotes the formation of an L12-ordered phase with the dominating elements Ni, Cu and Al. TEM characterization after slow rate tensile tests indicated there were the different precipitation behaviours at 700°C and 750°C. It was revealed that the occurrence of L12-ordered Ni-Cu-Al phase depends on temperature and Ni content. This opens up new opportunities to promote the formation of L12-ordered phase in Fe-based austenitic heat-resistance steels and benefit high-temperature mechanical properties.
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De Hosson, J. T. M. "Superlattice dislocations in L12 ordered alloys and in alloys containing L12 ordered precipitates." Materials Science and Engineering 81 (August 1986): 515–23. http://dx.doi.org/10.1016/0025-5416(86)90288-0.

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Gayle, Frank W., and John B. VanderSande. "Characterization of Rapidly Solidified Aluminum-Lithium Alloys." Proceedings, annual meeting, Electron Microscopy Society of America 43 (August 1985): 26–29. http://dx.doi.org/10.1017/s0424820100117224.

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Aluminum-lithium alloys are presently the subject of much research due to the effectiveness of lithium in reducing density, raising elastic modulus and providing for high strength. The strengthening precipitate is the metastable, L12-ordered Al3Li (Cu3Au prototype), or δ'. In binary alloys, δ’ precipitates homogeneously with a spherical shape, coherent with the aluminum matrix. These lithium-containing alloys suffer from poor ductility and fracture toughness, however, which has been attributed to 1) the shear-able nature of the δ’ precipitate, resulting in work softening and slip localization on the relevant slip planes, and 2) precipitate free zone formation along high angle grain boundaries.In a previous paper we proposed that Zr could partially substitute for Li in δ', resulting in a ternary Al3(Li,Zr) phase, which we call δ”. It was anticipated that such a phase would be more resistant to dislocation shear than δ’ from observation of deformation behavior of Al-Zr alloys containing the coherent L12-ordered Al3Zr precipitate.
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Moritani, Tomokazu, Masahiro Ota, Takao Kozakai, and Minoru Doi. "TEM Observations of Two-Phase Microstructure Formed by Phase Separation of Gamma-Prime Precipitates in Ni-Al-Si Alloys." Materials Science Forum 561-565 (October 2007): 2361–64. http://dx.doi.org/10.4028/www.scientific.net/msf.561-565.2361.

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The phase-separation behaviour of γ’ precipitates in Ni-7.1Al-6.7Si alloy was investigated by means of transmission electron microscopy (TEM). When the alloy is aged at 1173K, coherent spherical γ’ particles having ordered L12 structure appear in γ matrix having disordered A1 structure. When the two-phase microstructure of γ + γ’ is aged at 973K, spherical γ particles precipitate in the individual γ’ precipitates. In the course of ageing at 973K, the new γ particles grow keeping the spherical shape, their number gradually decreases and finally γ particles aging at 1173K gradually change their shape from sphere to cuboid, but do not practically change their size, i.e. such phase-separation behaviour brings the decelerated growth of γ’ precipitates.
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Wang, Rui, Yilei Fu, Guoliang Xie, Zifan Hao, Shuai Zhang, and Xinhua Liu. "The Microstructure and Mechanical Properties of Cu-20Ni-20Mn Alloy Fabricated by a Compact Preparation Process." Metals 10, no. 11 (November 18, 2020): 1528. http://dx.doi.org/10.3390/met10111528.

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A novel compact preparation process has been developed to produce a Cu-20Ni-20Mn alloy. This process involves heating-cooling combined mould (HCCM) continuous casting, a solution treatment at 800 °C, rolling at room temperature and a final ageing step at 450 °C. This process eliminates two hot deformation processes, namely, hot forging and hot rolling, greatly improving production efficiency and reducing production costs compared with the traditional preparation process. The alloy fabricated by this process was found to have excellent mechanical properties. Additionally, the formation of precipitated phases during the ageing step is accelerated by this new process. The hardness of the samples reaches 476 HV after ageing for 10 h. Stable, ordered precipitates of Ni3Mn(L12 phase) are observed in the rolled specimen, and the orientation relationship between the copper matrix and ordered Ni3Mn phase (L12 phase) is [200]Cu//[010]Ni3Mn and [011]Cu//[011]Ni3Mn. Precipitation strengthening is the main reason for the increase of strength of the sample during the ageing process. The mechanical properties and ageing precipitation process of the alloy are affected by the rolling process. The precipitation rate of the rolled sample is greatly increased during the ageing process, leading to a larger amount of precipitates.
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Jang, Ok Jun, Cheol-Woong Yang, and Dong Bok Lee. "Transmission Electron Microscopy Characterization of Thermomechanically Treated Al3Ti–(8, 10, 15)% Cr Intermetallics." Microscopy and Microanalysis 19, S5 (August 2013): 89–94. http://dx.doi.org/10.1017/s1431927613012403.

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AbstractThe ordered L12-type Al3Ti–(8, 10, 15)% Cr intermetallic compounds, namely, Al67Ti25Cr8, Al66Ti24Cr10, and Al59Ti26Cr15, were prepared by induction melting followed by thermomechanical treatment. Their microstructure, compositional variation, and crystal structure were characterized using X-ray diffraction, optical microscopy, and scanning and transmission electron microscopy equipped with energy-dispersive spectroscopy. The Al67Ti25Cr8 alloy consisted of the L12-Al3Ti matrix and precipitates of α2-Ti3Al, D022-Al3Ti, and γ-TiAl. The Al66Ti24Cr10 and Al59Ti26Cr15 alloys consisted of the L12-Al3Ti matrix and grains of α-TiAl and β-Cr.
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Eggeler, Y. M., K. V. Vamsi, and T. M. Pollock. "Precipitate Shearing, Fault Energies, and Solute Segregation to Planar Faults in Ni-, CoNi-, and Co-Base Superalloys." Annual Review of Materials Research 51, no. 1 (July 26, 2021): 209–40. http://dx.doi.org/10.1146/annurev-matsci-102419-011433.

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The mechanical properties of superalloys are strongly governed by the resistance to shearing of ordered precipitates by dislocations. In the operating environments of superalloys, the stresses and temperatures present during thermomechanical loading influence the dislocation shearing dynamics, which involve diffusion and segregation processes that result in a diverse array of planar defects in the ordered L12 γ′ precipitate phase. This review discusses the current understanding of high-temperature deformation mechanisms of γ′ precipitates in two-phase Ni-, Co-, and CoNi-base superalloys. The sensitivity of planar fault energies to chemical composition results in a variety of unique deformation mechanisms, and methods to determine fault energies are therefore reviewed. The degree of chemical segregation in the vicinity of planar defects reveals an apparent phase transformation within the parent γ′ phase. The kinetics of segregation to linear and planar defects play a significant role in high-temperature properties. Understanding and controlling fault energies and the associated dislocation dynamics provide a new pathway for the design of superalloys with exceptional properties.
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Vorontsov, V. A., R. E. Voskoboinikov, and Catherine M. F. Rae. "Prediction of Mechanical Behaviour in Ni-Base Superalloys Using the Phase Field Model of Dislocations." Advanced Materials Research 278 (July 2011): 150–55. http://dx.doi.org/10.4028/www.scientific.net/amr.278.150.

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The “Phase-Field Model of Dislocations” (PFMD) was used to simulate shearing of gamma-prime precipitate arrays in single crystal turbine blade superalloys. The focus of the work has been on the cutting of the L12 ordered precipitates by a<112>{111} dislocation ribbons during Primary Creep. The Phase Field Model presented incorporates specially developed Generalised Stacking Fault Energy (–surface) data obtained from atomistic simulations. The topography of this surface determines the shearing mechanisms observed in the model. The merit of the new –surface, is that it accounts for the formation of extrinsic stacking faults, making the model more relevant to creep deformation of superalloys at elevated temperatures.
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Dissertations / Theses on the topic "L12 ordered precipitates"

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Bansal, Ujjval. "Development of a coarsening resistant microstructure in precipitation strengthened aluminium alloys with Zr, Ta and Hf." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5237.

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The work herein aims at developing precipitation-strengthened aluminium-copper (Al-Cu) alloys that can meet the current challenges of the aeronautical and automobile sectors to increase the fuel efficiency where operating temperatures are above 200 ℃. The present study shows the effect of micro-additions of Zr, Ta and Hf in designing the newer generation of high strength Al-Cu alloys by microstructural engineering using a three-step heat treatment route. Prior ageing (400-450 ℃) before solutionizing is effective to form L12 ordered coherent precipitates. However, discontinuous precipitation is a challenge that can be avoided by micro-additions of Si with Hf. Further, ageing at 190 ℃ resulted in a dense distribution of strengthening θ"/θ' plates, nucleated heterogeneously on these L12 ordered precipitates resulting in a significant improvement in mechanical properties. The synergistic coupling of high and low-temperature strengthening phases resulted in the slower growth of θ"/θ' plates. The higher number density of θ"/θ' plates along with L12 ordered precipitates in the α-Al matrix rationalize the observed higher yield strength in Zr, Ta and Hf modified Al-Cu alloys. The reduction in the coarsening rate of θ' plates in the modified Al-Cu alloys was observed during a long time exposure at 250 ℃. Atomic-resolution composition analysis reveals the partitioning of slow diffusing elements to the θ' plates, which delays their coarsening. It induces a high-temperature stable microstructure with 250 MPa of yield strength at 250 ℃.
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Conference papers on the topic "L12 ordered precipitates"

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Zhao, Bingbing, Xianping Dong, Feng Sun, and Lanting Zhang. "Introduction of L12-Ordered Precipitation to Alumina-Forming Austenitic Heat-Resistant Steels With Low Ni Content." In ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/gt2017-63621.

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Alumina-forming austenitic (AFA) heat-resistant steels have been reported as a promising new class of steels in recent years with potential applications in advanced ultra-supercritical power plants. It is well known that L12-ordered γ’ phase is the most important precipitate for high-temperature strengthening in Ni-based superalloys and it can be stabilized by increasing the Ni content in heat-resistant steels. In the current work, the evolution of L12-ordered precipitates were compared in the Cu-bearing AFA alloys with 20, 27 and 35 wt.% Ni. After slow tensile tests at 700°C (∼2 × 10−5 s−1), L12-ordered precipitates occurred in all the alloys. Alloy AFA27 displayed the most densely distributed L12-particles in the matrix, whose ultimate tensile strength was also the highest. However, the L12-ordered precipitates were only observed in alloy AFA27 after the slow tensile test at 750°C due to the thermodynamic and kinetic reasons. Flow curves of slow tensile tests indicated different precipitation behaviors at 700°C and 750°C. Chemical composition analysis and thermodynamic calculation revealed that the occurrence of L12-ordered Ni-Cu-Al phase depends on temperature, Ni content and the atomic ratio of Ni/Al. This opens up new opportunities to promote the formation of L12-ordered phase in Fe-based austenitic heat-resistant steels with low Ni content and benefits high-temperature strengthening.
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Suzuki, Ken, Takuya Murakoshi, and Hideo Miura. "Crystallinity Degradation Caused by Alloying Elements Diffusion During Creep of Ni-Base Superalloy." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-53722.

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High temperature mechanical properties of Ni-base superalloys are improved by the fine cuboidal γ’ (Ni3Al) precipitates orderly-dispersed in the γ matrix (Ni-rich matrix) because the dispersed texture in a grain inhibits dislocation motion. However, it is well known that directional coarsening of the γ’ precipitates perpendicular to a principal stress occurs not only during creep loading but also during cyclic loading and, the formation of the raft causes the decreasing of high temperature strength drastically. Therefore, it is very important to evaluate the damage of the alloys caused by creep and fatigue loading based on the change of their micro texture. In this study, the change of crystallinity of the Ni-base superalloys (CM247LC) under creep loading was analyzed by applying Electron Back-Scattered Diffraction (EBSD) method. The image quality (IQ) value obtained from the EBSD analysis was used for the quantitative evaluation of the crystallinity in the area where an electron beam of 10 nm in diameter was irradiated. The quality of the atomic alignment of both γ’ and γ phases was found to degrade with increasing creep damage. The degradation of crystallinity suggests that the ordered L12 structure of Ni3Al became disordered and the density of dislocations and vacancies increased. However, KAM (Kernel Average Misorientation) value did not change significantly with increasing creep damage. Therefore, the dominant factor of the creep damage of this alloy is the strain-induced diffusion of elements under loading, and the decrease of the crystallinity.
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Gerdt, L., M. Müller, M. Heidowitzsch, J. Kaspar, E. Lopez, M. Zimmermann, C. Leyens, A. Hilhorst, and P. J. Jacques. "Alloy Design of Feedstock Material for Additive Manufacturing—Exploring the Al-Co-Cr-Fe-Ni-Ti Compositionally Complex Alloys." In ITSC 2023. ASM International, 2023. http://dx.doi.org/10.31399/asm.cp.itsc2023p0414.

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Abstract The need for sustainable use of resources requires continuous improvement in the energy efficiency and development of new approaches to the design and processing of suitable materials. The concept of high entropy alloys (HEAs) has recently been extended to more general compositional complex alloys (CCAs) and multi-principal element alloys (MPEAs). One of the major challenges on the way to application of these alloys is the extensive design and selection efforts due to the great variety of possible compositions and its consequences for workability and resulting material properties. The favorable high-temperature strength of Ni-based and Co-based superalloys is ascribed to a defined γ/γ’ structure consisting of a disordered FCC A1 matrix and ordered L12 γ’ precipitates. In the current work we extended this design concept to CCAs, allowing disordered BCC A2 and ordered B2 phases in additions or in substitution of the original γ/γ’ structure. We used a high-throughput screening approach combining CALPHAD-based computational tools with in situ alloying by means of laser cladding. Wall-type specimens with gradient composition in the system Al-Co-Cr-Fe-Ni-Ti with varying Al, Ti and Cr content were analyzed. The combined modelling and experimental screening approach was demonstrated to be a powerful tool for designing new high performance AM-ready feedstock.
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Suzuki, Ken, and Hideo Miura. "Stress-Induced Acceleration of the Change of Microstructure of Ni-Base Superalloy CM247LC." In ASME 2017 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/imece2017-70314.

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The degradation process of Ni-base superalloy CM247LC was investigated experimentally under the creep loading at 900°C. The initial excellent high-temperature strength of this alloy is attributed to its micro texture, the fine binary phase such as cuboidal γ’ (Ni3Al) precipitates orderly dispersed in the γ matrix (Ni-rich matrix). However, it was observed that γ’ precipitates started to coarse perpendicular to the applied uniaxial load direction during high temperature creep loading. The disappearance of the strengthened micro texture caused the acceleration of the crack growth along the phase boundaries of the layered texture and seriously degrades the strength of this material. Therefore, not only the outlook of micro texture but also the changes of the atomic configuration and atomic concentration which were based on the atomic diffusion behavior was investigated for the further explication of rafting mechanism more in detail. It was found that the distribution of Image Quality (IQ) value which was obtained from EBSD analysis monotonically shifted to lower values and the full width of half maximum became wider as the creep loading time increased. This degradation of the order of atomic alignment indicated that lattice defects density increased and ordered superlattice structure (Ll2 structure) became disordered. In addition, the initial periodic distributions of component elements which corresponded to the fine periodic alignment of the γ and γ’ phases also disappeared and the concentration of each element became uniform even though both the γ and γ’ phases still remained even after rafting. The observed creep damage of CM247LC was, therefore, dominated by the degradation of the order of atomic arrangement, and this degradation was attributed to the strain-induced atomic diffusion of component elements. It is very important, therefore, to suppress this strain-induced acceleration of atomic diffusion in this alloy by modifying the microstructure of this alloy.
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Takahashi, Motoki, Ken Suzuki, and Hideo Miura. "Atomic Diffusion Induced Damage of Ni-Base Super Alloy at Elevated Temperature." In ASME 2016 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2016. http://dx.doi.org/10.1115/imece2016-67592.

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Ni-base superalloys consisting of binary phases such as cuboidal γ’ (Ni3Al) precipitates orderly dispersed in the γ matrix (Ni-rich matrix) have been generally used for rotor blades in energy power plants. However, fine dispersed γ’ precipitates are coarsened perpendicularly to the applied load direction during high temperature creep loading. As this phenomenon called “Rafting” proceeds, the strengthened micro texture disappears and then, cracks starts to grow rapidly along the boundaries of the layered texture. Thus, it is very important to evaluate the change of the crystallinity of the alloy in detail for explicating the atomic scale damage process. In this study, the change of the micro-texture of the Ni-base superalloy (CM247LC) was observed by using EBSD method. The change in the crystallinity was evaluated using both Kernel Average Misorientation (KAM) and image quality (IQ) values. The KAM value indicates the dislocation density and the IQ value shows the order of atom arrangement in the observed area. As a result, KAM value showed no significant change with increasing the creep damage. On the other hand, the IQ value monotonically shifted to lower values and the average IQ value gradually decreased as the creep loading time increased. Decreasing IQ value without change in KAM value implies that the density of point defects such as vacancies mainly increased under creep loading and ordered Ll2 structure became disordered. Therefore, the creep damage of this alloy is mainly dominated by not the accumulation of dislocations, but the increase in the disorder of atom arrangement in the micro texture caused by the diffusion of component elements.
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