Measurement of the creep behavior of thin ZrNi metallic glass films – a comparison between nanoindentation relaxation, nanoindentation creep and lab-on-chips experiments

The characterization of the time-dependent behavior of thin metallic glass films is one of the key-issue for surface engineering. Such a measurement requires loading a constant material volume located in the thin film. Unfortunately, this condition is not fulfilled in the commonly used creep nanoindentation testing, contrary to micro tensile lab-on-chip experiments or micropillar compression testing. In this paper, we show that nanoindentation relaxation is an efficient alternative to nanoindentation creep. For that purpose, an extensive study of ZrNi metallic glasses viscoplastic behavior is performed using several experimental set-up (lab on chips, nanoindentation relaxation, nanoindentation creep, constant strain rate, ...). An innovative nanoindentation methodology is used to perform long-term relaxation tests up to 10 h with excellent reproducibility. It consists in maintaining a constant contact area during the test by controlling the contact stiffness between the tip and the material. Nanoindentation relaxation, constant strain rate loading and lab-on-chips data lead to similar values of apparent activation volume and strain rate sensitivity, whereas nanoindentation creep clearly overestimates the activation volume (Fig 1). Finite element modelling of nanoindentation creep and nanoindentation relaxation also confirms this trend. We evidence, thanks to the long-term indentation relaxation test that the underlying deformation mechanisms remain unchanged on the entire investigated strain rate range. Please click Additional Files below to see the full abstract