The effect of nanoindentation load on creep behavior of Mo-3.5 %Nb-0.4 %W monocrystal with different crystallographic orientations

Creep performance of molybdenum (Mo) alloy monocrystals is vital for their long-term service in nuclear reactors. And it usually varies greatly in different crystallographic orientations. Nanoindentation is an efficient and convenient method to understand creep behavior of the expensive Mo monocrystals. This paper studies the effect of nanoindentation load on room temperature creep in three orientations with extensive concerns in industrial applications for new Mo-3.5 %Nb-0.4 %W monocrystals. The results indicate that the hardness in (111) orientation is higher than that in (110) and (112) orientations, and their hardness gradually decreased with the rising of peak load or indentation depth. Meanwhile, (111) orientation exabits a better creep resistance compared to (110) and (112) orientations. The differences of the hardness and creep resistance in above-mentioned orientations are attributed to the differences in the difficulty and quantity of activating slip systems due to anisotropic structure of the monocrystals. Further analyzing results reveal that creep displacement, creep stress, strain rate sensitivity and activation volume are closely correlated with indentation depth during nanoindentation creep, indicating an indentation size effect on creep behavior similar to hardness.