Influence of Composition on Nanoindentation Response of Ni-Zr Alloy Thin Films

Variation in composition of an alloy thin film can alter its microstructure, which provides control over its nanomechanical behavior. To explore this idea, we fabricate thin films of Ni-Zr binary alloys with three different compositions and degrees of crystallinity. At low Zr-content, the microstructure is nanocrystalline, which becomes a mixture of amorphous and nanocrystalline phases at intermediate Zr-content. Further, the increase in Zr-content yields a predominantly amorphous film. Nanoindentations of the films reveal negative strain rate sensitivities over the investigated range of composition, although the effect becomes more pronounced with an increase in the Zr-content. Furthermore, the experiments render a closer view of the nanoindentation creep deformation of these Ni-Zr thin films. In particular, we have examined the influence of loading strain rate and composition on the creep compliance and retardation spectra, which provide valuable insight into the timescales associated with the time-dependent relaxation mechanisms. While the decrease in crystallinity mitigates the creep resistance, an increase in the loading strain rate is found to give rise to fast relaxation mechanisms corresponding to relatively smaller timescales. This study also introduces and highlights the prospects of analyzing the instantaneous strain rate sensitivity measured during the nanoindentation creep, which shows temporal features qualitatively analogous to that of the retardation spectra.