Loading rate sensitivity of nanoindentation creep in polycrystalline Ni films

Nanoindentation creep tests in Ni thin films with 3,000 nm thickness were performed with different loading times (5, 10, 20, 30, and 50 s) under the holding load 5,000 mu N and holding time 30 s to investigate the dependence of the indentation creep behavior on the loading rate. The results show that significant indentation loading rate sensitivity on stress exponent and hardness was found, which shows that the stress exponent increases with indentation loading rate. In contrast, the elastic modulus decreases slightly (more or less 1%) due to a longer loading time. Based on the experimental results, we infer that the creep phenomena observed were probably induced by plasticity.