Abstract:

With instrumented nanoindentation, incipient plasticity of two as-cast BCC TiZrNbTa and TiZrNbTaMo high-entropy alloys (HEAs) are investigated in terms of pop-in events during loading, to characterize the dislocation behavior in these solid-solution alloys. It is shown that the maximum shear stress (τ_max) required for dislocation nucleation is determined to be 1/16-1/12 and 1/18-1/14 of shear modulus for the TiZrNbTa and TiZrNbTaMo HEAs, respectively, which is nearly comparative to the theoretical shear stress of these alloys. The activation volumes of dislocation nucleation the TiZrNbTa and TiZrNbTaMo HEAs are determined to be 1.2b³ for and 1.3b³, respectively, which is substantially irrespective of alloying with Mo. Furthermore, activation volumes of these two HEAs are on the order of cubic burger’s vector and only one-third of the value for TiZrHfNb HEA, suggesting that a heterogeneous nucleation of dislocation took place in a way of direct atom-vacancy exchange, rather than of the cooperative motion of several atoms. These findings reveal the unique feature in deformation of BCC solid-solution complex alloys.

Key words: High-entropy alloys, Nanoindentation, Refractory metals, BCC phase, Incipient plasticity