Local slip resistances in equal-molar MoNbTi multi-principal element alloy

Xu, Shuozhi; Su, Yanqing; Jian, Wu-Rong; Beyerlein, Irene J.

doi:10.1016/j.actamat.2020.10.042

Cited by 67 publications

(12 citation statements)

References 84 publications

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“…For pure bcc metals, it is well known, e.g., from in situ TEM experiments 49 , 58 , that edge dislocations play a minor role in strengthening at low and moderate temperatures due to their higher mobility. However, from recent studies for bcc RHEAs, the role of the edge dislocations has been suggested to play a more important role in the high-temperature regime 21 , 26 , 59 ; High energy barriers for edge dislocation motion in RHEA have also been investigated through atomic simulations 60 ; additionally, a large fraction of non-screw segments has been observed during the glide of dislocations in such alloys 16 . In this work, we have calculated the velocities of the screw and edge dislocations over a wide range of temperatures in such a RHEA and have shown that the mobility of the edge dislocations does decrease with increasing temperature due to phonon drag; moreover, at the same time, the velocity of the screw dislocations moving by a double-kink mechanism is found to increase with temperature due to a lowering of the free-energy barrier for kink-pair nucleation.…”

Section: Resultsmentioning

confidence: 99%

Atomistic simulations of dislocation mobility in refractory high-entropy alloys and the effect of chemical short-range order

et al. 2021

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Refractory high-entropy alloys (RHEAs) are designed for high elevated-temperature strength, with both edge and screw dislocations playing an important role for plastic deformation. However, they can also display a significant energetic driving force for chemical short-range ordering (SRO). Here, we investigate mechanisms underlying the mobilities of screw and edge dislocations in the body-centered cubic MoNbTaW RHEA over a wide temperature range using extensive molecular dynamics simulations based on a highly-accurate machine-learning interatomic potential. Further, we specifically evaluate how these mechanisms are affected by the presence of SRO. The mobility of edge dislocations is found to be enhanced by the presence of SRO, whereas the rate of double-kink nucleation in the motion of screw dislocations is reduced, although this influence of SRO appears to be attenuated at increasing temperature. Independent of the presence of SRO, a cross-slip locking mechanism is observed for the motion of screws, which provides for extra strengthening for refractory high-entropy alloy system.

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Section: Resultsmentioning

confidence: 99%

Atomistic simulations of dislocation mobility in refractory high-entropy alloys and the effect of chemical short-range order

et al. 2021

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“…[ 13 ] Last but not least, non‐screw character dislocations could be introduced in body‐centered‐cubic (BCC) RHEAs to enhance the exceptional high‐temperature hardening. [ 14–20 ] Taking these intrinsic material characteristics in alloys design, a novel RHEA with a single‐phase BCC structure was designed for greatly improving high‐temperature performance. The new RHEA contains equimolar elements of Cr, Mo, Nb, and V with large atomic‐size and elastic‐modulus mismatches, but presents reliable phase stability at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

Superior High‐Temperature Strength in a Supersaturated Refractory High‐Entropy Alloy

et al. 2021

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Refractory high‐entropy alloys (RHEAs) show promising applications at high temperatures. However, achieving high strengths at elevated temperatures above 1173K is still challenging due to heat softening. Using intrinsic material characteristics as the alloy‐design principles, a single‐phase body‐centered‐cubic (BCC) CrMoNbV RHEA with high‐temperature strengths (beyond 1000 MPa at 1273 K) is designed, superior to other reported RHEAs as well as conventional superalloys. The origin of the high‐temperature strength is revealed by in situ neutron scattering, transmission‐electron microscopy, and first‐principles calculations. The CrMoNbV's elevated‐temperature strength retention up to 1273 K arises from its large atomic‐size and elastic‐modulus mismatches, the insensitive temperature dependence of elastic constants, and the dominance of non‐screw character dislocations caused by the strong solute pinning, which makes the solid‐solution strengthening pronounced. The alloy‐design principles and the insights in this study pave the way to design RHEAs with outstanding high‐temperature strength.

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“…All inputs into PFDD are physical, such as the elastic constants, lattice parameters, and USFE, and are obtained from the MTP calculations in the preceding sections. In an MPEA, the resistance to dislocation glide is not homogeneous within the material due to variations in local composition [7,8,[35][36][37]. A dislocation will only be affected by the type and arrangement of atomic elements within a radius of a few Burgers vectors [38].…”

Section: Phase-field Frameworkmentioning

confidence: 99%

Multi-scale Investigation of Chemical Short-Range Order and Dislocation Glide in the MoNbTi and TaNbTi Refractory Multi-Principal Element Alloys

Fey¹,

Li²,

Hu³

et al. 2022

Preprint

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Refractory multi-principal element alloys (RMPEAs) are promising materials for high-temperature structural applications. Here, we investigate the role of chemical short-range ordering (CSRO) on dislocation glide in two model RMPEAs -TaNbTi and MoNbTi -using a multi-scale modeling approach. A highly accurate machine learning interatomic potential was developed for the Mo-Ta-Nb-Ti system and used to demonstrate that MoNbTi exhibits a much greater degree of SRO than TaNbTi and the local composition has a direct effect on the unstable stacking fault energies (USFE). From mesoscale phase-field dislocation dynamics simulations, we find that increasing SRO leads to higher mean USFEs, thereby increasing the stress required for dislocation glide. The gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, amount of hardening. Finally, we show how the morphology of an expanding dislocation loop is affected by the applied stress, with higher SRO requiring higher applied stresses to achieve smooth screw dislocation glide.

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Local slip resistances in equal-molar MoNbTi multi-principal element alloy

Cited by 67 publications

References 84 publications

Atomistic simulations of dislocation mobility in refractory high-entropy alloys and the effect of chemical short-range order

Atomistic simulations of dislocation mobility in refractory high-entropy alloys and the effect of chemical short-range order

Superior High‐Temperature Strength in a Supersaturated Refractory High‐Entropy Alloy

Multi-scale Investigation of Chemical Short-Range Order and Dislocation Glide in the MoNbTi and TaNbTi Refractory Multi-Principal Element Alloys

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