Mo content-dependent hardness and microstructural evolution of CoCrNiMo_x medium entropy alloys

Amorphous/crystalline nanocomposites have received extensive attention due to their excellent mechanical properties and good structural stability. However, the underlying mechanism of the strengthening effect related to the microstructural length scale remains controversial. By altering Mo content of CoCrNiMo_x medium entropy alloys, in the present study, microstructural feature and length scale dependent hardness was evaluated. Unlike conventional amorphous/crystalline nanocomposites, we demonstrate here that the hardness followed by a strengthening to softening transition dependent on the Mo content. The maximum hardness is achieved in the specimen with largest amorphous layer thickness, indicating dislocation-mediated process within crystalline phase plays dominating role in achieving higher strengthening effects, which dependent on both length scales of amorphous and crystal phases and the interactions between them.