Hard glass-ceramic coating by microwave processing

Microwave processing was employed in the present work to obtain hard glass-ceramic coating on nickel based superalloy substrate. The glass-ceramic coatings were developed from a glass based on MgO–Al2O3–TiO2 system. The coatings were characterized through X-ray diffractometry (XRD), scanning electron microscopy (SEM), image analysis, surface roughness measurement and hardness evaluation by depth sensitive indentation (DSI) technique. Surface and cross-sectional SEM examinations of the polished and etched samples revealed that under identical combination of heat treatment temperature and time, the microwave processed coating contained finer crystallites than the sizes of the crystallites obtained in the conventionally processed coating. The microwave processed glass-ceramic coating exhibited surface roughness (Ra) value much lower than that of the conventionally processed glass-ceramic coating. DSI results confirmed that the microwave processed coating possessed much higher hardness (∼6 GPa) compared to that of the conventionally processed coating.