Size effect and anisotropy in cold rolled Zr-base bulk metallic glasses during nanoindentation

A series of instrumented nanoindentation tests have been performed in control loading rate mode on Zr52.5Cu18Ni14.5Al10Ti5 (VIT105) and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (VIT106A) as-cast and various cold rolled samples to investigate the indentation size effect (ISE) in three perpendicular planes i.e., rolling-width (RW), normal-rolling (NR) and normal-width (NW) planes at peak loads in the range of 50 mN - 500 mN. The hardness, reduced modulus and dynamic hardness have reduced with the increase of indentation depth in NR, RW and NW planes. The as-cast and cold rolled BMGs exhibit normal ISE for NR, RW and NW planes. The size effect has been analyzed using power law, Nix-Gao model, and proportional specimen resistance model suggesting that dynamic mechanical softening and the friction between the indenter and specimen are the underlying reasons behind the observed ISE.