Examination of CO₂ laser-induced rapid solidification structures on magnesia partially stabilised zirconia and the effects thereof on wettability characteristics

The formation mechanism of rapidly solidified microstructures in a magnesia partially stabilised zirconia (MgO-PSZ) following CO₂ laser radiation has been investigated. The influence of laser processing parameters on the microstructures of this material was analysed based on a review of the basic concepts of solidification, the theories of constitutional suppercooling and morphological stability. The different microstructures that were brought about by various laser parameters and appeared across the same track were examined based on the CO₂ laser beam profile of a transverse electromagnetic mode (TEM₀₁). The contact angle measurement revealed a better wettability characteristic of CO₂-laser-modified MgO-PSZ. The clear differences were observed in the change in contact angle for glycerol across the range of rapid solidification microstructures obtained with various power densities. It was therefore determined that the degree of rapid surface resolidification could be the most predominant element governing the wettability characteristics of the MgO-PSZ. The sharp reduction of contact angle for glycerol took place when the cellular microstructure appeared and might be accompanied by the onset of melting on the modified surface of the MgO-PSZ. Moreover, the CO₂ laser treatment also brought about the change in the surface oxygen content and surface roughness. The analysis showed that surface oxygen content was also an influential factor in changing the wettability characteristics of the MgO-PSZ, whilst surface roughness was found to play an insignificant role. The work provides the clear evidence that laser radiation can be a workable and controllable technique to modify the wetting characteristic of the MgO-PSZ.