Effects of chemical randomness on strength contributors and dislocation behaviors in a bcc multiprincipal element alloy

Molecular dynamics simulations for dislocation motion are conducted in a body centered cubic TaCrVW multiprincipal element alloy with different chemical randomness based on a machine learning potential. The simulated critical stress for dislocation motion in samples with an increasing level of randomness is analyzed in terms of three contributions: (1) Peierls stress (from 438 to 431 MPa), (2) strengthening from the average fault energy (from 261 MPa to near zero), and (3) strengthening due to local fluctuations of fault energy from the average value (from 394 to 566 MPa). As the alloy randomness increases, the Peierls stress as predicted from lattice distortion is rather invariant within the range studied, while there is a clear decreasing trend of the average fault energy and hence the associated strengthening. There is an increasing trend of strength contribution (3) as the alloy randomness increases, which offsets the decreasing trend of strength contribution (2). The overall strength of the TaCrVW alloy is therefore rather invariant within the range 964-1259 MPa with different randomness. The present work elucidates the physical basis of strength in the studied TaCrVW alloy.