Multi-cycling instrumented nanoindentation of a Ti-23Nb-0.7Ta-2Zr-1.20 alloy in annealed condition

In this study, depth-dependent mechanical properties (i.e. hardness, elastic modulus, and indentation size effect) as well as strain rate sensitivity of a new class of titanium based alloys, Ti-23Nb-0.7Ta-2Zr-1.20, are considered. To this end, local deformation micro-mechanisms of this alloy are investigated systematically through a constant-strain rate (CSR) instrumented nanoindentation testing technique. The CSR nanoindentation tests were performed at ambient (room) temperature with nominal indentation depths of 100-2000 nm and strain rates of 0.005, 0.05, and 0.5 s(-1) using a Berkovich pyramidal indenter. Nanoindentation is a particularly reliable tool for studying elastic/plastic behavior of metallic alloys. Large strain gradients around the indenter should reveal and help clarify the thermally activated mechanisms contributing to the plastic deformation processes which can quantitatively be interpreted by examining the rate sensitivity index, m, and activation volume. Indentation results show that the strain rate sensitivity and activation volume, Burger's vector times activation area, are depth-dependent phenomena revealing different controlling plastic deformation mechanisms.