Strengthening mechanism of CoCrNiMox high entropy alloys by high-throughput nanoindentation mapping technique

A novel nanoindentation mapping technique was employed to correlate the microstructure, composition and mechanical properties of the fcc, laves and lamellae in CoCrNiMox high-entropy alloys with varying Mo content. The results suggest that the Young's modulus of the 3 constituents were comparable, averaging ≈230 GPa. Despite this, the hardness was quite different. The fcc phase in CoCrNiMox was mainly strengthened by a solute strengthening mechanism, and the hardness was increased from ≈3.98 GPa to ≈4.45 GPa, as the atomic percentage of Mo in fcc increased from ≈7.4% to 15.4%. A solute strengthening model a accounting lattice distortion was employed to correlate the strengthening effect in fcc with Mo content. The laves phase was rich in Mo composition (≈28.6%) and exhibited an ultrahigh hardness, ≈9.13 GPa, which was ≈2 times higher than that of fcc phase. Finally, the lamellae colonies, made up by alternative fcc and laves phases, had an intermediate hardness, ≈6.36 GPa. This was well explained by a rule-of-mixture model.