First-principles investigation of plane faults and thermodynamics in BCC (TiZrHf)1-xMx (M=Nb, Mo, Ta) medium entropy alloys

The newly developed BCC TiZrHf based multi-principal element alloys (MPEAs) can simultaneously guarantee high strength and good ductility. However, until now, the theoretical research on their stacking faults (SFs) and twins associated with the dislocation in plastic deformation have scarcely been studied due to their large computation amount and complexity, and thus the underlying mechanisms are still mysterious. In this work, we have investigated the effects of three types of substitution elements, namely, Nb, Mo and Ta, on the SF energy (SFE) curves of (110) plane of TiZrHf based medium entropy alloys (MEAs) along [001]ˎ [110] and [111] directions, twinning faults on (112) plane, based on the first-principles (FP) calculations in conjunction with the special quasi-random structures (SQS) method. With the increase of Nb, Ta and Mo concentrations, the unstable SFE γ_us along [001], [110] and [111] directions show a wavier increasing trend, and the effect of Mo is more pronounced. The boundary energy of the twins TS₁, TS₂ and TS₃ also show the wavier increasing tendency, and they are all larger than that of pure TiZrHf alloy. We have conducted an in-depth investigation into the thermodynamic properties of TiZrHf-based alloys doped with Nb, Ta, and Mo, owing to their exceptional high-temperature performance.