Coating behavior and surface hardening of Pd₇₇Cu₆Si₁₇ thin film metallic glass on AZ31 magnesium alloy

Pd₇₇Cu₆Si₁₇ (PCS) thin film metallic glasses (TFMGs) with high glass forming ability and hardness were selected as a hard coating for improving the surface hardness of AZ31 magnesium alloy. Both microindentation and nanoindentation tests were conducted on specimens with various PCS film thicknesses from 30 to 2000 nm. The apparent hardness and the relative indentation depth (β) were integrated using a quantitative model. The interaction parameters involved and relative hardness values were extracted from iterative calculations. According to the results, surface hardness can be enhanced greatly by PCS TFMGs in the shallow region, followed by gradual decrease with increasing β ratio. In addition, specimens with thinner coatings (e.g., 200 nm) showed greater substrate-film interaction and those with thick coatings (e.g., 2000 nm) became prone to film cracking. The optimum TFMG coating thickness in this study was estimated to be around 200 nm.