Significant improvement in surface hardness of Zr-based metallic glass by nanosecond pulsed laser irradiation in graphite powder water suspension

Metallic glasses (MGs) have shown promising application prospects as structural materials due to their unique mechanical properties. While, for broadening their application as functional materials, significant improvement in surface hardness of MGs is required. Accordingly, in this study, laser carbonization of MGs was attempted by irradiating the Zr-based MG surface immersed in graphite powder water suspension using a nanosecond pulsed laser. Nanoindentation response and surface morphologies of the initial and irradiated surfaces were characterized in detail. The results indicated that the hardness of the laser-irradiated surfaces was increased by 130 %- 200 % (from 6.407 GPa to 19.193 GPa), and as well, the serrated flows in load-depth curves and the surface shear bands around the residual indent disappeared, suggesting the change in micro-scale plastic deformation behaviors of the laser-irradiated surfaces. Furthermore, the chemical composition of the initial and irradiated surfaces was analyzed by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS), which showed that the irradiated surfaces were carbonized in the graphite powder water suspension. Accordingly, the increase in surface hardness was due to the formation of the hard crystalline phases.