Structural and mechanical modifications induced on Cu47.5Zr47.5Al5 metallic glass by surface laser treatments

We have investigated the effects of surface laser treatment (SLT) on the structure, mechanical properties and wettability of Cu47.5Zr47.5Al5 metallic glass alloy. SLT has been carried out at three different intensities with the aim of inducing variable surface damage and tuneable changes in the resulting properties. X-ray diffraction characterization and scanning electron microscopy observations reveal that the alloy laser treated at 28.5 A remains amorphous while the alloy treated at 29 A becomes partially crystalline (CuZr B2 phase). When the alloy is treated at 30 A, it is mainly composed of copper and zirconium oxides. Nanoindentation tests, carried out on-top of the as-cast and laser-treated surfaces, reveal that SLT at 28.5 A causes an increase in hardness, which can be attributed to annihilation of free volume (i.e. structural relaxation). Conversely, hardness values of the alloy laser-treated at 29 A are almost the same as those of the as-cast alloy. This could be ascribed to the counterbalance effect between the softer nature of the CuZr B2 phase and the harder nature of the remaining relaxed amorphous phase. Larger hardness values are observed for the alloy laser treated at 30 A as a result of oxide phase formation.