Mechanistic origin of high strength in refractory BCC high entropy alloys up to 1900K

Abstract

The body centered cubic (BCC) high entropy alloys MoNbTaW and MoNbTaVW show exceptional strength retention up to 1900K. The mechanistic origin of the retained strength is unknown yet is crucial for finding the best alloys across the immense space of BCC HEA compositions. Experiments on Nb-Mo, Fe-Si and Ti-Zr-Nb alloys report decreased mobility of edge dislocations, motivating a theory of strengthening of edge dislocations in BCC alloys. Unlike pure BCC metals and dilute alloys that are controlled by screw dislocation motion at low temperatures, the strength of BCC HEAs can be controlled by edge dislocations, and especially at high temperatures, due to the barriers created for edge glide through the random field of solutes. A parameter-free theory for edge motion in BCC alloys qualitatively and quantitatively captures the strength versus temperature for the MoNbTaW and MoNbTaVW alloys. A reduced analytic version of the theory then enables screening over >600,000 compositions in the Mo-Nb-Ta-V-W family, identifying promising new compositions with high retained strength and/or reduced mass density. Overall, the theory reveals an unexpected mechanism responsible for high temperature strength in BCC alloys and paves the way for theory-guided design of stronger high entropy alloys.

Unusual activated processes controlling dislocation motion in body-centered-cubic high-entropy alloys

“…This is different from conventional BCC metals, where the strength is governed solely by screw dislocations. In fact, an edge-dislocation-based model has already been proposed recently for interpreting the solid-solution strengthening in BCC refractory HEAs ( 21 ). Second, an appreciable activation barrier is present for detrapping from locally favorable regions (inhomogeneity on nanometer- or subnanometer scale), which can be regarded as yet another “high-entropy” effect, in this case arising from the high variability of local configuration and composition almost inevitable in a heavily concentrated solution of multiple principal elements.…”

Enhanced Hardness in High‐Entropy Carbides through Atomic Randomness

“…Hence, the range of the Peierls stress could be directly determined. Instead of the incremental method used in the previous work, [ 14 ] in this work a half‐interval search algorithm was used and searching stopped when the range of the Peierls stress was less than 0.5 GPa. The correction due to the periodic image interactions [ 19 ] was not applied as the trend rather than the exact values of the Peierls stress was important in this work.…”

“…[ 13 ] Maresca and Curtin screened over 600 000 high‐entropy compositions in the Mo‐Nb‐Ta‐V‐W family to identify high retained strength alloys using an edge dislocation motion theory. [ 14 ] In the current work, the Peierls stress was used as a hardness indicator for the design of HECs.…”

Effect of Solution Treatment on the Shape Memory Functions of (TiZrHf)50Ni25Co10Cu15 High Entropy Shape Memory Alloy

“…In recent years, studies on HEAs have extended to non-equiatomic compositions for better desired or unique properties, such as light-weight [ 9 ], high phase stability [ 10 ], outstanding radiation resistance [ 11 ], etc. Assocaited with these newly explored properties, interpretations of fundamental mechanisms in HEAs have been investigated with both experimental and simulation techniques [ 12 , 13 , 14 , 15 , 16 ]. With the understanding of the atomic distribution and deformation mechanisms, the design and research progress of HEAs can step further [ 17 ].…”