Effect of alloying elements on stacking fault energies and twinnabilities in high‐entropy transition‐metal carbides

Abstract

Twinning is a fundamental mechanism behind the simultaneous increase in the strength and ductility of high‐entropy alloys. Similar approaches may contribute to the remarkable improvements of the mechanical properties of high‐entropy ceramics. In this study, the stacking fault energies (SFEs) and twinnabilities of a novel category of ZrNbTa‐based high‐entropy transition‐metal carbides (HETMCs) are investigated in terms of their generalized stacking fault energy curves (γ‐curves) via first‐principle calculations. The γ‐curves show that dislocation nucleation in ZrNbTa‐based HETMCs occurs more easily than that of unary transition metal (TM, TM = Zr, Nb, Ta, Hf, Ti, V) carbides. When a pre‐existing intrinsic stacking fault (ISF) is considered, C‐ vertices (TM‐ mirror) twinning fault (TF) more likely forms and TF may be more stable than ISF. The stable SFEs of C‐ vertices ISF and TF decrease with the addition of Hf, Ti, and V atoms to (ZrNbTa)C owing to the severe local lattice distortion. The calculated barrier energies and twinnabilities further indicate that twinning is possible for the selected ZrNbTa‐based HETMCs. Theoretical twinnabilities (τa) decrease in the following sequence: (ZrNbTa)C > (ZrNbTaHfTi)C > (ZrNbTaHf)C > (ZrNbTaHfTiV)C. Thus, the addition of Hf, Ti, and V atoms to (ZrNbTa)C may decrease the twinning probability. This study may be used as a guide for the design of twinning‐induced plasticity HETMCs with excellent mechanical properties.

Metal-carbide eutectics with multiprincipal elements make superrefractory alloys

“…The present observation that many stacking faults and deformation twins appear in the multicomponent carbide phase in the (TaC) 0.9 MPEA supports that the multicomponent carbide has a lower stacking fault energy than those of conventional monocarbides, which leads to the improved fracture toughness of high-entropy carbide ( 49 , 50 ). Similar to many reported MPEAs, this reduced stacking fault energy is mainly attributable to the chemical effect of the high entropy ( 51 ), in which the addition of alloying elements can decrease the stacking fault energy and promote plastic deformation by twinning and stacking faults ( 44 , 52 ). Meanwhile, the formation of deformation twins is considered local stress dependent, which occurs with increasing plastic strains at high temperatures ( 53 ).…”