High hardness, low youngs modulus and low friction of nanocrystalline ZrW 2 laves phase and Zr 1-xW x thin films

Abstract

Zr1−xWx nanocrystalline films of Zr-W solid solutions and ZrW2 Laves phase were synthesized by magnetron co-sputtering. Large values of the H/E ratio up to 0.09 are observed for grain sizes in the nanometer range along with a hardness above 10 GPa and Young's modulus below 230 GPa. H/E values are correlated with the developed surface of grain boundaries suggesting an elastic deformation mostly handled by the grain boundaries. This is associated to friction coefficients comparable to those of metallic glass surfaces. In contrast to fragile bulk Laves phases, no cracks were detected at the film surface after indentation and scratch test of nanocrystalline ZrW2. The friction coefficient of such films against diamond tip was in the range 0.08–0.15, similarly to metallic glass surfaces.