Development of BMG-B2 nanocomposite structure in HAZ during laser surface processing of ZrCuNiAlTi bulk metallic glasses

Abstract

In this study, the laser scanning speed used during laser surface processing of a Zr-based bulk metallic glass (BMG) was optimised to obtain amorphous structure in the melt zone and nanocomposite structure in the heat affected zone (HAZ). For this aim, Zr65.7Ti3.3Al3.7Ni11.7Cu15.6 (wt.%) BMG foils with a 100 µm thickness were laser surface treated at the different speeds. The microstructural characteristics of the melt zone and HAZ of the different samples were studied using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and high-resolution transmission electron microscope (HRTEM). Nanoindentation testing was employed to evaluate the mechanical properties. In addition, molecular dynamic (MD) simulation was used to discover the deformation mechanisms. The results showed that at a laser speed of 22.6 mm/s, the amorphous structure remained, and an improvement in mechanical properties was obtained in the HAZ. The HRTEM images revealed that in the HAZ of the optimum sample, a BMG-B2 nanocomposite structure was formed that improved the mechanical response of the HAZ, considerably. The MD results showed that the existence of B2 phase avoid stress reduction after starting of plastic deformation and even a higher stress during plastic deformation was recorded.