Mechanical and corrosion behaviour of as-cast and annealed Zr60Cu20Al10Fe5Ti5 bulk metallic glass

The influence of thermally-induced structural relaxation and crystallization on the mechanical and electrochemical corrosion behaviour of a Zr60Cu20Al10Fe5Ti5 metallic glass has been studied. The hardness, H, and reduced Young's modulus, Er, increase upon annealing at 648 K (i.e., close to the glass transition) from H = 6.7 GPa and Er = 79.4 GPa (as-cast state) to H = 7.0 and Er = 86.7 GPa (structurally relaxed state). The influence of the free volume annihilation, caused by the annealing treatments, on these mechanical properties is discussed. Further increase in H and Er occurs after annealing at 873 K, when the sample becomes fully crystalline, probably due to the formation of Zr2Cu phase. The crystallization also increases the H/Er ratio (which is indicative of the wear resistance), from 0.083 in the as-cast condition to 0.102, whereas structural relaxation does not have a clear effect on this parameter. Annealing close to the glass transition is also beneficial to improve the corrosion resistance and, in particular, the resistance to pitting, when this alloy is immersed in simulated body fluid (Hank's solution). The corrosion potential shifts from −0.214 V to −0.043 V (vs. Ag|AgCl) and the current density decreases from 3.017 × 10−4 A/cm2 to 8.846 × 10−6 A/cm2 after annealing at 648 K, mainly because of the free volume reduction. The corrosion potential is maximum (i.e., −0.022 V) and the corrosion density minimum (i.e., 1.428 × 10−6 A/cm2) when the sample becomes fully crystalline