不同晶体取向Mo-Nb单晶的纳米压痕尺寸效应

The load-displacement curves, the elastic modulus, the indentation morphology, the nanohardness-loading depth and elastic recovery of high purity Molybdenum-Niobium single crystal were investigated by nanoindentation and scanning probe microscopy. The results show that Mo-Nb single crystal has a good plastic deformation ability. Mo-Nb crystal plane undergoes elastic deformation and plastic deformation during the loading-unloading process, and the load-displacement curve does not show discontinuity, which demonstrates that cracks and brittle fracture are not formed in the indents. Moreover, the pile-up behavior around indents reveals that Mo-Nb single crystal has a relatively low processing strain hardening tend. The nanohardness and elastic modulus of Mo-Nb single crystal were measured by continuous stiffness measurement (CSM), and a size effect on the nanohardness and elastic modulus was observed, which decreases with the increase of indentation depth. The order of the different nanohardness and elastic modulus is: (110) crystal plane > (112) crystal plane > (111) crystal plane. The Nix-Gao model was employed to analyze the nanoindentation mechanical characteristics of Mo-Nb single crystal, and the intrinsic hardness in the limit of infinite depth (H₀) are 3.96, 2.61and 3.47 GPa, respectively; the size effect index (i) are 0.18, 0.16 and 0.18, respectively. The characteristic length (h^*) of (110), (111), (112) crystal plane are 1196, 2753 and 1559 nm, respectively. Mo-Nb single crystal has an obvious size effect when the indentation depth is below the characteristic length, and the size effect becomes more insignificant when indentation depth is deeper than the characteristic length. The nanoindentation size effect will disappear as the impression are deeper than 4106, 5645 and 4693 nm, respectively.