Статті в журналах: "Planar Fault Energies"

1

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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2

Woodward, C., J. M. MacLaren, and S. Rao. "Electronic structure of planar faults in TiAl." Journal of Materials Research 7, no. 7 (July 1992): 1735–50. http://dx.doi.org/10.1557/jmr.1992.1735.

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The mechanical behavior of intermetallic alloys is related to the mobility of the dislocations found in these compounds. Currently the effect of bonding on dislocation core structure and its influence on deformation behavior is not well understood. However, the unusual properties of these materials, such as the anomalous temperature dependence of flow stress observed in TiAl, are derived in part from the aspects of bonding that determine dislocation mobility. Several recent studies have suggested a particular relationship between directional bonding in TiAl and dislocation mobility. To understand better the flow behavior of high temperature intermetallics, and as a step toward bridging the gap between electronic structure and flow behavior, we have calculated the electronic structure of various planar faults in TiAl. The self consistent electronic structure has been determined using a layered Korringa Kohn Rostoker (LKKR) method which embeds the fault region between two semi-infinite perfect crystals. Calculated defect energies in stoichiometric TiAl agree reasonably well with other theoretical estimates, though overestimating the experimental (111) anti-phase boundary (APB) energy, found for Ti46Al54. We approximate the energy of the (111) APB for the Al-rich stoichiometry by calculating the energy of Al antisites near that defect plane. The calculated (111)APB energy decreases by 6% in going from stoichiometric TiAl to Ti46Al54. The overall hierarchy of fault energies is found to be associated with the number of crystal bond states that are disrupted by the introduction of the fault plane. However, the hierarchy of fault energies is inconsistent with the traditionally accepted ordering. Changes in bonding taking place in the vicinity of the planar defects are illustrated through the density of states and charge density plots. A three body atomistic model is introduced to parameterize the bonding observed in TiAl. The L10 lattice (c/a = 1.00), within a second nearest neighbor three body model, yields a (111)APB energy which is the sum of the complex and superlattice-intrinsic stacking fault energies.

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3

Jagatramka, Ritesh, Junaid Ahmed, and Matthew Daly. "The evolution of deformation twinning microstructures in random face-centered cubic solid solutions." Journal of Applied Physics 133, no. 5 (February 7, 2023): 055107. http://dx.doi.org/10.1063/5.0135538.

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The varied atomic arrangements in face-centered cubic (FCC) solid solutions introduce atomic-scale fluctuations to their energy landscapes that influence the operation of dislocation-mediated deformation mechanisms. These effects are particularly pronounced in concentrated systems, which are of considerable interest to the community. Here, we examine the effect of local fluctuations in planar fault energies on the evolution of deformation twinning microstructures in randomly arranged FCC solid solutions. Our approach leverages the kinetic Monte Carlo (kMC) method to provide kinetically weighted predictions for competition between two processes: deformation twin nucleation and deformation twin thickening. The kinetic barriers underpinning each process are drawn from the statistics of planar fault energies, which are locally sampled using molecular statics methods. kMC results show an increase in the fault number densities of solid solutions relative to a homogenized reference, which is found to be driven by the fluctuations in planar fault energies. Based on kMC relations, an effective barrier model is derived to predict the competition between deformation twinning nucleation and thickening processes under a fluctuating planar fault energy landscape. A key result from this model is a measurement of the length-scale over which the influence of local fluctuations in planar fault energies diminish and nucleation/thickening-dominated behaviors converge to bulk predictions. More broadly, the tools developed in this study enable examination of the influence of chemistry and length-scale on the evolution of deformation twinning mechanisms in FCC solid solutions.

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4

Farkas, Diana, and Christophe Vailhe. "Planar fault energies and dislocation core spreading in B2 NiAl." Journal of Materials Research 8, no. 12 (December 1993): 3050–58. http://dx.doi.org/10.1557/jmr.1993.3050.

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We present computer simulation results for the planar faults involved in core spreading of 〈100〉 and 〈111〉 dislocations. Seven γ surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111}, and {122}). Stable APB's are observed in the {110} and {112} planes, but they are deviated from the exact 1/2a〈111〉 position. No other stable planar fault was observed. The fact that a stable minimum is observed deviated from the 1/2〈111〉 position suggests the possibility of different dissociation reactions for the 〈111〉 screw dislocation in the {110} and {112} planes. The fact that no other stable minima were observed in the γ surfaces indicates that no true core dissociation is expected for the 〈100〉 dislocations. We propose that dislocation core spreading in various planes can be understood in terms of the directions of lowest restoring forces observed for the corresponding γ surfaces.

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5

Liu, Lili, Liwan Chen, Youchang Jiang, Chenglin He, Gang Xu, and Yufeng Wen. "Temperature Effects on the Elastic Constants, Stacking Fault Energy and Twinnability of Ni3Si and Ni3Ge: A First-Principles Study." Crystals 8, no. 9 (September 14, 2018): 364. http://dx.doi.org/10.3390/cryst8090364.

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The volume versus temperature relations for Ni 3 Si and Ni 3 Ge are obtained by using the first principles calculations combined with the quasiharmonic approach. Based on the equilibrium volumes at temperature T, the temperature dependence of the elastic constants, generalized stacking fault energies and generalized planar fault energies of Ni 3 Si and Ni 3 Ge are investigated by first principles calculations. The elastic constants, antiphase boundary energies, complex stacking fault energies, superlattice intrinsic stacking fault energies and twinning energy decrease with increasing temperature. The twinnability of Ni 3 Si and Ni 3 Ge are examined using the twinnability criteria. It is found that their twinnability decrease with increasing temperature. Furthermore, Ni 3 Si has better twinnability than Ni 3 Ge at different temperatures.

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6

Wiezorek, J. M. K., and C. J. Humphreys. "On the hierarchy of planar fault energies in TiAl." Scripta Metallurgica et Materialia 33, no. 3 (August 1995): 451–58. http://dx.doi.org/10.1016/0956-716x(95)00212-e.

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7

Liu, Lili, Yelu He, Dingxing Liu, Xiaozhi Wu, and Rui Wang. "Temperature-Dependent Generalized Planar Fault Energy and Twinnability of Mg Microalloyed with Er, Ho, Dy, Tb, and Gd: First-Principles Study." Advances in Materials Science and Engineering 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/7365906.

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The generalized planar fault energies, Rice criterion ductility, and twinnability of pure Mg and Mg-RE (RE = Er, Ho, Dy, Tb, and Gd) alloys at different temperature have been investigated using density functional theory. It is shown that all the fault energies and twinnability in the same materials decrease with increasing temperature. However, the ductility has the opposite change trend. On the other hand, alloying rare earth elements will generally decrease the fault energies and increase the ductility and twinnability of Mg at different temperature. It is interesting to note that alloying larger atomic radius will enhance the ductility of Mg more easily and alloying smaller radius will make twinning tendency of Mg more easily. Finally, the electron structure further reveals the underlying mechanisms for the reduction of fault energies with the addition of rare earth elements.

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8

Kibey, S., J. B. Liu, D. D. Johnson, and H. Sehitoglu. "Generalized planar fault energies and twinning in Cu–Al alloys." Applied Physics Letters 89, no. 19 (November 6, 2006): 191911. http://dx.doi.org/10.1063/1.2387133.

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9

Zhu, Yaxin, Zhouqi Zheng, Minsheng Huang, Shuang Liang, and Zhenhuan Li. "Modeling of solute hydrogen effect on various planar fault energies." International Journal of Hydrogen Energy 45, no. 15 (March 2020): 9162–73. http://dx.doi.org/10.1016/j.ijhydene.2020.01.107.

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10

Wen, Y. F., and J. Sun. "Generalized planar fault energies and mechanical twinning in gamma TiAl alloys." Scripta Materialia 68, no. 9 (May 2013): 759–62. http://dx.doi.org/10.1016/j.scriptamat.2012.12.032.

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11

Zhang, J. Y., P. S. Branicio, and D. J. Srolovitz. "Planar fault energies of copper at large strain: A density functional theory study." Journal of Applied Physics 116, no. 10 (September 14, 2014): 103512. http://dx.doi.org/10.1063/1.4895075.

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12

Vamsi, K. V., and S. Karthikeyan. "High-throughput estimation of planar fault energies in A3B compounds with L12 structure." Acta Materialia 145 (February 2018): 532–42. http://dx.doi.org/10.1016/j.actamat.2017.10.029.

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13

Fu, C. L., J. Zou, and M. H. Yoo. "Elastic constants and planar fault energies of Ti3Al, and interfacial energies at the interface by first-principles calculations." Scripta Metallurgica et Materialia 33, no. 6 (September 1995): 885–91. http://dx.doi.org/10.1016/0956-716x(95)00313-k.

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14

Kawabata, T., and O. Izumi. "Effect of the axial ratio on planar fault energies in L10-type superlattice structures." Philosophical Magazine A 55, no. 6 (June 1987): 823–41. http://dx.doi.org/10.1080/01418618708214386.

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15

Zhang, W. J., and F. Appel. "Weak-beam TEM study on planar fault energies of Al-lean TiAl-base alloys." Materials Science and Engineering: A 334, no. 1-2 (September 2002): 59–64. http://dx.doi.org/10.1016/s0921-5093(01)01763-4.

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16

Gbemou, Kodjovi, Jean Marc Raulot, Vincent Taupin, and Claude Fressengeas. "Continuous Modeling of Dislocation Cores Using a Mechanical Theory of Dislocation Fields." Materials Science Forum 879 (November 2016): 2456–62. http://dx.doi.org/10.4028/www.scientific.net/msf.879.2456.

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A one-dimensional model of an elasto-plastic theory of dislocation fields is developed to model planar dislocation core structures. This theory is based on the evolution of polar dislocation densities. The motion of dislocations is accounted for by a dislocation density transport equation where dislocation velocities derive from Peach-Koehler type driving forces. Initial narrow dislocation cores are shown to spread out by transport under their own internal stress field and no relaxed configuration is found. A restoring stress of the lattice is necessary to stop this infinite relaxation and it is derived from periodic sinusoidal energy of the crystal. When using the Peierls sinusoidal potential, a compact equilibrium core configuration corresponding to the Peierls analytical solution is obtained. The model is then extended to use generalized planar stacking fault energies as an input and is applied to the determination of properties of planar dislocation cores in crystalline materials. Dissociations of edge and screw dislocation cores in basal and prismatic planes of Zirconium are shown.

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17

Vailhé, C., and D. Farkas. "Shear faults and dislocation core structures in B2 CoAl." Journal of Materials Research 12, no. 10 (October 1997): 2559–70. http://dx.doi.org/10.1557/jmr.1997.0340.

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Interatomic potentials of the embedded atom and embedded defect type were derived for the Co–Al system by empirical fitting to the properties of the B2 CoAl phase. The embedded atom potentials reproduced most of the properties needed, except that, in using this method, the elastic constants cannot be fitted exactly because CoAl has a negative Cauchy pressure. In order to overcome this limitation and fit the elastic constants correctly, angular forces were added using the embedded defect technique. The effects of angular forces to the embedded atom potentials were seen in the elastic constants, particularly C44. Planar fault energies changed up to 30% in the {110} and {112} γ surfaces and the vacancy formation energies were also very sensitive to the non-central forces. Dislocation core structures and Peierls stress values were computed for the 〈100〉 and 〈111〉 dislocations without angular forces. As a general result, the dislocations with a planar core moved for critical stress values below 250 MPa in contrast with the nonplanar cores for which the critical stress values were above 1500 MPa. The easiest dislocations to move were the 1/2〈111〉 edge superpartials, and the overall preferred slip plane was {110}. These results were compared with experimental observations in CoAl and previously simulated dislocations in NiAl.

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18

Kim, C. S., and S. I. Kwun. "Ultrasonic Evaluation of Cyclically Deformed Microstructures of Cu and Cu-35Zn Alloy." Materials Science Forum 475-479 (January 2005): 4117–20. http://dx.doi.org/10.4028/www.scientific.net/msf.475-479.4117.

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Ultrasonic nondestructive evaluation (NDE) technique has been applied to investigate the cyclically deformed microstructures of a Cu and Cu-35Zn alloy. These materials, which had different stacking fault energies, were cyclically deformed in order to examine the ultrasonic reaction with different dislocation substructures. The observation of a dislocation structure using TEM and the measurement of the ultrasonic NDE parameters were performed after various fatigue deformation in order to clarify the relationship between them. The ultrasonic velocity was observed to decrease with increasing fatigue life fraction in both materials, which was attributed to the increasing dislocation density, resulted from the cyclic deformation. The increasing rate of ultrasonic attenuation in Cu with a cell structure that evolved during cyclic deformation was higher than that in the Cu-35Zn alloy, which had a planar array. This suggests that the dislocation cell structure is more sensitive to the change in the ultrasonic parameters than the planar array structure formed during cyclic deformation.

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19

Varn, D. P., G. S. Canright, and J. P. Crutchfield. "Inferring planar disorder in close-packed structures via ∊-machine spectral reconstruction theory: structure and intrinsic computation in zinc sulfide." Acta Crystallographica Section B Structural Science 63, no. 2 (March 16, 2007): 169–82. http://dx.doi.org/10.1107/s0108768106043084.

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We apply ∊-machine spectral reconstruction theory to analyze structure and disorder in four previously published zinc sulfide diffraction spectra and contrast the results with the most common alternative theory, the fault model. In each case we find that the reconstructed ∊-machine provides a more comprehensive and detailed understanding of the stacking structure, often detecting stacking structures not previously found. Using the ∊-machines reconstructed for each spectrum, we calculate a number of physical parameters – such as configurational energies, configurational entropies and hexagonality – and several quantities – including statistical complexity and excess entropy – that describe the intrinsic computational properties of the stacking structures.

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20

Kumar, Kaushlendra, R. Sankarasubramanian, and Umesh V. Waghmare. "Tuning planar fault energies of Ni3Al with substitutional alloying: First-principles description for guiding rational alloy design." Scripta Materialia 142 (January 2018): 74–78. http://dx.doi.org/10.1016/j.scriptamat.2017.08.021.

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21

Woodward, C., and J. M. Maclaren. "Planar fault energies and sessile dislocation configurations in substitutionally disordered Ti-Al with Nb and Cr ternary additions." Philosophical Magazine A 74, no. 2 (August 1996): 337–57. http://dx.doi.org/10.1080/01418619608242147.

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22

Liu, Lili, Rui Wang, Xiaozhi Wu, Liyong Gan, and Qunyi Wei. "Temperature effects on the generalized planar fault energies and twinnabilities of Al, Ni and Cu: First principles calculations." Computational Materials Science 88 (June 2014): 124–30. http://dx.doi.org/10.1016/j.commatsci.2014.03.005.

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23

Liu, Yifan, Xianjun Guan, Yanjie Zhang, Zipeng Jia, Simin Liang, and Xiaowu Li. "Effect of Short-Range Ordering on the Grain Boundary Character Distribution Optimization of FCC Metals with High Stacking Fault Energy: A Case Study on Ni-Cr Alloys." Crystals 12, no. 12 (December 14, 2022): 1822. http://dx.doi.org/10.3390/cryst12121822.

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The critical roles of short-range ordering (SRO) in the grain boundary character distribution (GBCD) optimization of Ni-Cr alloys with high stacking fault energies were experimentally studied by thermomechanical treatments. It is found that, with the enhancement of the SRO degree (or the increase in Cr content), the dislocation slip mode changes from wavy slip to planar slip, and even deformation twins (DTs) appear in the cold-rolled Ni-40at.%Cr alloy. Within the lower level of Cr content (≤20 at.%), the optimized result of GBCD is conspicuous with the increase in Cr content. As the Cr content is higher than 20 at.%, the GBCD optimization of Ni-Cr alloys cannot be further enhanced, since the cold rolling induced DTs would hinder the growth of twin related domains during subsequent annealing.

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24

Han, Dong, Jin-Xian He, Xian-Jun Guan, Yan-Jie Zhang, and Xiao-Wu Li. "Impact of Short-Range Clustering on the Multistage Work-Hardening Behavior in Cu–Ni Alloys." Metals 9, no. 2 (January 29, 2019): 151. http://dx.doi.org/10.3390/met9020151.

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The work-hardening behavior of Cu–Ni alloys with high stacking-fault energies (SFEs) is experimentally investigated under uniaxial compression. It is found that, with the increase of Ni content (or short-range clustering, SRC), the flow stress of Cu–Ni alloys is significantly increased, which is mainly attributed to an enhanced contribution of work-hardening. An unexpected multistage (including Stages A, B, and C) work-hardening process was found in this alloy, and such a work-hardening behavior is essentially related to the existence of SRC structures in alloys. Specifically, during deformation in Stage B (within the strain range of 0.04–0.07), the forming tendency to planar-slip dislocation structures becomes enhanced with an increase of SRC content (namely, increase of Ni content), leading to the occurrence of work-hardening rate recovery in the Cu–20at.% Ni alloy. In short, increasing SRC in the Cu–Ni alloy can trigger an unexpected multistage work-hardening process, and thus improve its work-hardening capacity.

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25

Lv, Xinliang, Shenghu Chen, Qiyu Wang, Haichang Jiang, and Lijian Rong. "Temperature Dependence of Fracture Behavior and Mechanical Properties of AISI 316 Austenitic Stainless Steel." Metals 12, no. 9 (August 28, 2022): 1421. http://dx.doi.org/10.3390/met12091421.

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A combination of fractographic and metallographic analysis during tensile tests over the temperature ranging from 20 °C to 750 °C were carried out to investigate the fracture behaviors and deformation modes so as to clarify the temperature dependence of mechanical properties of AISI 316 austenitic stainless steel. Planar slip mode of deformation was observed during tensile tests at 20 °C due to a relatively low SFE (stacking fault energies). Pronounced planar slip characteristics were observed in the range of 350–550 °C, and the resultant localized deformation led to the formation of shear bands. The dislocation cross-slip was much easier above 550 °C, leading to the formation of cell/subgrain structures. The preferential microvoid initiation and subsequent anisotropic growth behavior in the shear bands led to large-size and shallow dimples on the fracture surfaces in the range of 350–550 °C. However, the microvoid tended to elongate along the tensile direction in the localized necking region above 550 °C, resulting in small-size and deep dimples. The shear localization reduced the uniform deformation ability and accelerated the fracture process along shear bands, leading to a plateau in uniform elongation and total elongation in the range of 350–550 °C. The higher capability to tolerate the localized deformation through sustained necking resulted in a significant increase in the total elongation above 550 °C.

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26

SINGH, A. K., R. SANKARASUBRAMANIAN, and T. K. NANDY. "Mobilities and dislocation energies of planar faults in an ordered A3B (D019) structure." Bulletin of Materials Science 36, no. 4 (August 2013): 677–86. http://dx.doi.org/10.1007/s12034-013-0521-9.

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27

Paidar, Václav, and Andriy Ostapovets. "Displacive Phase Transformations." Solid State Phenomena 150 (January 2009): 159–74. http://dx.doi.org/10.4028/www.scientific.net/ssp.150.159.

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Shear deformation and shuffling of atomic planes are elementary mechanisms of collective atomic motion that take place during displacive phase transformations. General displacements of atomic planes are examined, i.e. -surface type calculations extensively used for the stacking faults and crystal dislocations are applied to single plane shuffling and alternate shuffling of every other atomic plane producing in combination with homogeneous deformation the hcp structure (martensitic type) from the initial bcc structure (austenitic type). Similar approach considering shear type planar displacements leads to the Zener path between the bcc and fcc lattices. The effect of additional deformation required to obtain the close-packed atomic arrangements is examined as well. Finally, the influence of volume modification on phase transitions is investigated. The energies of various structural configurations are calculated using many-body potentials for the description of interatomic forces. Such atomic models are tested to check their suitability for investigation of the role of interfaces in the displacive structural transitions.

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28

Maclaren, J. M., and C. Woodward. "Electronic Structure of Planar Faults and Point Defects in High Temperature Intermetallics." MRS Proceedings 253 (1991). http://dx.doi.org/10.1557/proc-253-387.

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ABSTRACTFirst principles electronic structure calculations, using the layer Korringa-Kohn-Rostoker method, are reported for isolated planar faults in TiAl. The calculated fault energies are discussed in the context of suggested superdislocation separation reactions. The influence of dilute impurities on fault energies are treated using the coherent potentialapproximation. Using this approach, the variation of fault energies in TiAl resulting from stoichiometry changes and from the addition of Mn axe calculated, and compared to recent experimental data.

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29

Kumar, Mukul, T. J. Balk, and K. J. Hemker. "Measurement of Planar Fault Energies in Ni3Ge-Fe3Ge Intermetallic Alloys." MRS Proceedings 538 (1998). http://dx.doi.org/10.1557/proc-538-329.

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AbstractA combination of transmission electron microscopy (TEM) and image simulations has facilitated a highly quantitative measure of superdislocation dissociations. The experimental observations have been corrected for image shifts within the framework of anisotropic elasticity by comparison with simulated images. This allows experimental quantification of planar fault energies, thus providing a benchmark for first principles and atomistic simulations and fundamental insight towards alloy modeling and design. Such measurements of superdislocation dissociations on the order of 1-15 nm have been recorded for the pseudobinary Ni3Ge-Fe3Ge alloy system. These detailed measurements of fault widths obtained by weak-beam TEM observations of deformation structures will be presented and discussed as a function of alloy composition. The transition from anomalous to normal temperature dependence of yielding behavior in these alloys will also be discussed in terms of observed dislocation structures and planar fault energies calculated using the above measurements.

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30

Andritsos, E. I., and A. T. Paxton. "Effects of calcium on planar fault energies in ternary magnesium alloys." Physical Review Materials 3, no. 1 (January 16, 2019). http://dx.doi.org/10.1103/physrevmaterials.3.013607.

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31

Hirel, Pierre, Jean Furstoss, and Philippe Carrez. "A critical assessment of interatomic potentials for modelling lattice defects in forsterite Mg$$_2$$SiO$$_4$$ from 0 to 12 GPa." Physics and Chemistry of Minerals 48, no. 12 (November 11, 2021). http://dx.doi.org/10.1007/s00269-021-01170-6.

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AbstractFive different interatomic potentials designed for modelling forsterite Mg$$_2$$ 2 SiO$$_4$$ 4 are compared to ab initio and experimental data. The set of tested properties include lattice constants, material density, elastic wave velocity, elastic stiffness tensor, free surface energies, generalized stacking faults, neutral Frenkel and Schottky defects, in the pressure range $$0-12$$ 0 - 12 GPa relevant to the Earth’s upper mantle. We conclude that all interatomic potentials are reliable and applicable to the study of point defects. Stacking faults are correctly described by the THB1 potential, and qualitatively by the Pedone2006 potential. Other rigid-ion potentials give a poor account of stacking fault energies, and should not be used to model planar defects or dislocations. These results constitute a database on the transferability of rigid-ion potentials, and provide strong physical ground for simulating diffusion, dislocations, or grain boundaries.

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32

Zhu, Qi, Zhiliang Pan, Zhiyu Zhao, Guang Cao, Langli Luo, Chaolun Ni, Hua Wei, Ze Zhang, Frederic Sansoz, and Jiangwei Wang. "Defect-driven selective metal oxidation at atomic scale." Nature Communications 12, no. 1 (January 25, 2021). http://dx.doi.org/10.1038/s41467-020-20876-9.

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AbstractNanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned silver and palladium driven by individual stacking-faults and twin boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Planar-fault mediated diffusion of oxygen atoms is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by planar defects in metallic nanostructures, which could enable the modification of physiochemical performances in nanomaterials through defect engineering.

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33

Zapol, Peter, Larry A. Curtiss та Dieter M. Gruen. "First-Principles Study of π-Bonded (100) Planar Defects in Diamond". MRS Proceedings 538 (1998). http://dx.doi.org/10.1557/proc-538-371.

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AbstractA periodic density functional study of the high-energy π-bonded (100) stacking fault in diamond that can serve as a prototype of a twist grain boundary has been carried out. Information on formation energies, geometries and the electronic structure has been obtained. A single point electronic structure calculation of a ∑5 twist grain boundary based on the geometry taken from a molecular dynamics simulation has also been performed.

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34

Simmons, J. P., S. I. Rao, and D. M. Dimiduk. "Effect of Planar Fault Energies on Dislocation Core Structures and Mobilities in L10 Compounds." MRS Proceedings 288 (January 1992). http://dx.doi.org/10.1557/proc-288-335.

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35

Breidi, A., J. Allen, and A. Mottura. "First-principles calculations of thermodynamic properties and planar fault energies in Co3X and Ni3X L12compounds." physica status solidi (b) 254, no. 9 (May 16, 2017). http://dx.doi.org/10.1002/pssb.201600839.

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36

Li, Wei, Shuang Lyu, Yue Chen, and Alfonso H. W. Ngan. "Fluctuations in local shear-fault energy produce unique and dominating strengthening in metastable complex concentrated alloys." Proceedings of the National Academy of Sciences 120, no. 12 (March 13, 2023). http://dx.doi.org/10.1073/pnas.2209188120.

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Local chemical short-range ordering (SRO) and spatial fluctuations of planar fault energy are important features of multi-element and metastable complex concentrated alloys (CCAs). Arising from them, dislocations in such alloys are distinctively wavy in both static and migrating conditions; yet, such effects on strength have remained unknown. In this work, molecular dynamics simulations are used to show that the wavy configurations of dislocations and their jumpy motion in a prototypic CCA of NiCoCr are due to the local fluctuations of the energy of SRO shear-faulting that accompanies dislocation motion, with the dislocation getting pinned at sites of hard atomic motifs (HAMs) associated with high local shear-fault energies. Unlike the global averaged shear-fault energy which in general will subdue on successive dislocation passes, the local fluctuations in the fault energy always remain in a CCA, thus offering a strength contribution that is unique in such alloys. Analysis of the magnitude of this form of dislocation resistance shows that this is dominating over contributions due to elastic misfit of alloying elements and is in good agreement with strengths predicted from molecular dynamics simulations and experiments. This work has unfolded the physical basis of strength in CCAs, which is important for the development of these alloys into useful structural materials.

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37

Zhang, X. D., and M. H. Loretto. "Complex Anti Phase Domain Boundaries In A Gamma TiAl Alloy." MRS Proceedings 364 (1994). http://dx.doi.org/10.1557/proc-364-611.

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AbstractRecent work has shown that antiphase domains are observed in alloys based around TiAl if they are quenched from the alpha field. The present work has shown that the anti phase domain boundaries (APDBs) are in fact not simple APDBs but are composed of very thin (about 2 nm) 90° domains. Although the contrast is dominated by the fact there is a 1/2<101> displacement between the domains either side of this thin 90° domain, there is somewhat more complex contrast associated with the APDBs than the hard sphere model would predict. Annealing studies of the complex APDBs in a Ti49Al alloy have shown that the originally irregular APDBs in the quenched material facet on {111} planes. The significance of these observations is discussed in terms of mechanisms by which the APDBs are formed in TiAl and in terms of the planar fault energies in the Llo structure.

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38

John Balk, T., Mukul Kumar, and Kevin J. Hemker. "Relating Mechanical Properties with Dislocation Cores in Ni3Ge-Fe3Ge Intermetallic Alloys." MRS Proceedings 460 (1996). http://dx.doi.org/10.1557/proc-460-641.

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ABSTRACTThe transition from positive to negative temperature dependence of 0.2% yield stress is investigated m the model pseudo-binary Ni3Ge-Fe3Ge system. Ni3Ge and Fe3Ge, both Ll2 intermetallic alloys, show complete solid solubility as Fe is continuously substituted for Ni across the composition range. However, Ni3Ge exhibits the yield stress anomaly, whereas the yield stress of Fe3Ge shows a normal decline with temperature. Mechanical testing has verified this behavior, with the anomalous behavior gradually disappearing with increasing Fe content. It is proposed that this transition results from changes in the structure of dissociated superdislocation cores. Alloys with anomalous behavior from this system are characterized by the presence of screw superdislocations locked in the Kear-Wilsdorf (KW) configuration. Conversely, alloys with normal yield stress dependence are observed to contain curvilinear superdislocations that glide on the cube planes. Results from mechanical testing are presented and correlated with TEM observations of deformation structures. These results are discussed in light of planar fault energies determined through computer simulations of images.

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39

Balk, T. J., Mukul Kumar, O. N. Mryasov, A. J. Freeman, and K. J. Hemker. "Characterizing Deformation Mechanisms in Ni3Ge-Fe3Ge Intermetallic Alloys." MRS Proceedings 552 (1998). http://dx.doi.org/10.1557/proc-552-kk10.8.1.

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ABSTRACTThe Ni3Ge-Fe3Ge model system provides us with a unique opportunity to characterize the mechanisms of deformation in both anomalous and normal L12 intermetallic alloys. The elastic moduli of alloys in this system have been measured and used as benchmarks for first principles calculations. At 77K, increasing the Fe content has been found to result in a dramatic increase in flow stress. The Ni-rich alloys exhibit a yield strength anomaly, but as Ni is replaced by Fe, the anomalous temperature dependence gradually disappears, and no yield strength anomaly is observed for alloys with more than 25 at% Fe. At low temperatures and Fe contents, the deformation microstructure has been found to be dominated by Kear-Wilsdorf locking; but a transition from octahedral glide and Kear-Wilsdorf locking to cube glide is observed as either Fe content or temperature is increased. This transition is related to changes that occur in the core structures of dissociated superdislocations and planar fault energies measured through computer simulations of weak-beam TEM images.

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40

Rao, S., C. Woodward та P. M. Hazzledine. "The Interaction Between Dislocations and Lamellar Grain Boundaries in Pst γ Tiai". MRS Proceedings 319 (1993). http://dx.doi.org/10.1557/proc-319-285.

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AbstractIn lamellar TiAl the flat-plate geometry of the grains, the barriers to deformation across the grain boundaries and the coherency stresses all contribute to a marked anisotropy in the yield and fracture stresses of the material. Both yield and fracture occur at low stresses when the deformation is within the lamellae (soft mode) and they occur at high stresses when the deformation crosses the lamellae (hard mode). The anisotropy is enhanced by a new effect which can soften the soft mode and harden the hard mode: the geometry of the lamellar boundary produces degeneracies in the planar fault energies at the interfaces which enhance the mobilities of dislocations on these interfaces. These degeneracies modify the core structure of dislocations on or near the interfaces, consequently soft mode dislocations can dissociate widely and move more easily when their glide plane is contained in the interface. Hard mode dislocations can substantially reduce their core energies when intersecting a γ/γ interface, and subsequently become immobilized, by cross slipping on to the interface plane. This paper presents a discussion of the geometry and relative energies of the γ/γ interfaces using elements of Bollman O-lattice theory. In order to investigate the influence of the interfaces on dislocation core structure we have fit an empirical Embedded Atom Method (EAM) potential to the structural and elastic properties of bulk L10 TiAl. The mobility and core structure of the twinning dislocation at the 180° interface and the perfect, 1/2<110] screw dislocation at the 60° and 120° interfaces were calculated using molecular statics within the EAM. We have also studied the influence of one and two atomic step ledges on dislocation mobility in the 120° interface. We find in general that dislocations are more glissile on the γ/γ interfaces, as compared to bulk TiAl and that ledges are weak barriers to dislocation glide. The interfaces themselves are strong barriers to dislocation motion in the hard mode. We find that the 1/2<110] screw dislocations gliding on conjugate {111} planes are trapped at these interfaces, as a result of lower core energies for screw dislocations lying in the interface.

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41

Rao, Satish I., C. Woodward, and T. A. Parthasarathy. "Empirical Interatomic Potentials for L1O Tial and B2 Nial." MRS Proceedings 213 (1990). http://dx.doi.org/10.1557/proc-213-125.

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ABSTRACTRecent studies have suggested a particular relationship between the degree of covalent bonding in TiAl and the mobility of dislocation[1,2]. Ultimately such electronic effects In ordered compounds must dictate the dislocation core structures and at the same time the dislocation mobility within a given compound. However, direct modelling of line defects Is beyond the capability of todays electronic structure techniques. Alternatively, significant steps toward extending our understanding of the flow behaviour of structural intermetallics may come through general application of empirical interatomic potential methods for calculating the structure and mobility of defects. Toward this end, we have constructed semi-empirical interatomic potentials within the embedded atom formalism for L1O and B2 type structures. These potentials have been determined by fitting to known bulk structural and elastic properties of TIAl and NiAl, using least squares procedures. Simple expressions that relate the parameters of the potentials to the bulk properties are used in the fitting procedure. Calculations of dislocation core structures and planar fault energies using these potentials are considered. The differences between the optimized bulk properties predicted from the potentials and the values for these properties are discussed in terms of non-spherical nature of the electron density distribution. Empirical methods which incorporate these effects into interatomic potentials are briefly discussed.

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42

Khantha, M., V. Vitek, and D. P. Pope. "Dislocation Core Structures and Mechanical Behavior of DO22 Type Alloys." MRS Proceedings 213 (1990). http://dx.doi.org/10.1557/proc-213-229.

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ABSTRACTWe investigate the structures of dislocation cores in a model DO22 type intermetallic alloy in the absence of external stresses. The tetragonal distortion produces sessile configurations of superpartial dislocations even when the energies of planar faults are reasonably low. The influence of the core configurations on the mechanical behavior at low temperatures is discussed.

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43

Woodward, C., J. M. Maclaren, and S. Rao. "Electronic Structure of Planar Faults in Tial." MRS Proceedings 213 (1990). http://dx.doi.org/10.1557/proc-213-715.

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ABSTRACTThe mechanical behavior of intermetallic alloys is related to crystal bonding and the influence of bonding on the core structure of dislocations formed in these compounds. These combined effects influence the deformation behavior in an, as yet, undefined manner. However, in a way that gives rise to unusual behavior, such as the anomalous temperature dependence of flow stress observed in TiAl. Recent studies have suggested a particular relationship between the directional bonding in TiAl and dislocation mobility. To better understand the flow behavior of intermetallics, and as a beginning toward bridging the gap between electronic structure and flow behavior, we have calculated the electronic structure of various planar faults in TiAl. The self consistent electronic structure has been determined using the layered Korringa Kohn Rostoker (LKKR) method which embeds the region containing the defect between two semi-infinite perfect crystals. Calculated defect energies agree reasonably well with other theoretical estimates, though overestimating experimental values. The changes in bonding taking place in the vicinity of the planar defect will be discussed and illustrated through the density of states and charge density plots.

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44

Hampel, K., D. D. Vvedensky, and S. Crampin. "First-Principles Calculations of Stacking Faults and Grain Boundaries in Metals." MRS Proceedings 213 (1990). http://dx.doi.org/10.1557/proc-213-57.

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ABSTRACTA detailed understanding of planar defects plays an important role in the search for a comprehensive description of the mechanical behaviour of metals and alloys. We present calculations for isolated stacking faults and grain boundaries using the layer Korringa-Kohn-Rostoker method including an assessment of the force theorem, which has already proven itself in evaluating defect energies for elemental close-packed metals. These ab initio total energy calculations will be supplemented by a study of the changes in bonding and local magnetic properties near a symmetric Σ5 (310) grain boundary in Fe

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45

Brey, Dominik, Barbara Scherer, and Martin U. Schmidt. "Lattice defects in quinacridone." Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials 78, no. 5 (September 9, 2022). http://dx.doi.org/10.1107/s205252062200779x.

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Various lattice defects in the αI-phase of quinacridone (C20H12N2O2) were simulated using lattice-energy minimizations. αI-Quinacridone forms a chain structure in P 1, Z = 1. The molecules are connected by hydrogen bonds along [010], by π-stacking along [100] and by weak van der Waals interactions along [001]. αI-Quinacridone is inherently nanocrystalline. Lattice defects were calculated in correspondingly large supercells with up to 4464 atoms, using a previously evaluated force field. Vacancies, vacancy aggregates and interstitial molecules are energetically very unfavourable. A misorientation of a single molecule (flip around [010] by 180°) causes an energy increase of 243.7 kJ mol−1. Various edge and screw dislocations were investigated. A screw dislocation along [010] causes an energy increase of ΔE = 38.0 kJ mol−1 per molecule, all other line dislocations are even worse. In contrast, the rotation of an entire chain around the chain axis [010] by 180° leads to only a very small energy increase (ΔE = 1.6 kJ mol−1) and the real crystals probably contain a high number of such defects. Various planar defects were calculated, including different stacking disorders and misfit-layer structures with two different types of layers having different lateral periodicities. Stacking faults along [001] with herringbone stacking instead of parallel stacking are energetically quite favourable (ΔE = 2.2 kJ mol−1); the same is true for domains with misoriented molecules in the [001] direction. As an example for a bulk defect, domains are calculated in which blocks of 4 × 4 chains are rotated by 180° around [010], which leads to an energy increase of only 1.1 kJ mol−1. Twinning by mirroring at the (001) plane is energetically favourable (ΔE = 0.9 kJ mol−1). This twinning was observed in an HRTEM image. It is probable that the crystallites also contain rotations of chains, layers or blocks around [010] by 180°, but these defects cause only a very slight modification of the molecular packing, which was not observable in the HRTEM image. The lattice defects in αI-quinacridone investigated here provide an insight into lattice defects, their energies and local structures. Similar lattice defects are expected to occur also in other similar organic chain structures.

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