Anisotropy Characteristics of Micro- and Nano-mechanical Properties and Strain Rate Response of Mo-Nb-W Single Crystal

Mo-based single crystal is a key material for nuclear power generation components in deep space exploration ships. Optimizing alloy composition to achieve property improvement of single crystal materials is an important way to improve the power generation efficiency and service life of nuclear power sources. A novel Mo-Nb-W single crystal was prepared by electron beam suspension zone melting method, and the hardness (H), contact stiffness (S) and elastic modulus (E) of different oriented crystal planes were investigated by nanoindentation technique. The results show that there is no pop-in phenomenon in the load-displacement (P-h ) curves of the (111) crystal plane, and the plasticity index is high, which indicates that the plasticity in <111> direction is good. However, the pop-in steps appear in the P-h curves of both (110) and (112) crystal planes during nanoindentation, and the plasticity index is low, indicating that the plasticity in <111> and <112> directions is relatively poor. The hardness of the measured oriented crystal planes is gradually increased with the increase in strain rate due to the shortened relaxation time, while the contact stiffness and elastic modulus are slowly decreased as strain rate increases. There is significant anisotropy in the mechanical properties of Mo-Nb-W single crystal, and the hardness is ranked as H ((111)) > H ((110)) > H ((112)) . The order of contact stiffness and elastic modulus are as follows: S ((111)) > S- (112) > S ((110)) and E- (111) > E ((112)) > E ((110)) . The hardness of these mentioned oriented crystal planes is gradually decreased with the rise of indentation depth, and the (111) oriented crystal plane has the most obvious indentation size effect.