Microstructure Evolution of ZrO2 Particle During Manufacture of ZrO2 Thermal Barrier Coating by Laser Melt Injection

The ZrO2p/Ti-6Al-4 V metal matrix composites layer, which is a novel and promising thermal barrier coating, is produced in this study by the laser melt injection (LMI) process. The microstructure evolution of the ZrO2 particle during the LMI process is studied via X-ray diffraction, electron backscattered diffraction, and scanning electron microscopy. The results show that through solid-state diffusion, the size of sub-particle in the agglomerated ZrO2 particle increases, and the morphology transforms from spherical to polyhedral. Few monoclinic ZrO2 (m-ZrO2) is found in the ZrO2 particle after the LMI. Moreover, 35% of the metastable tetragonal ZrO2 (t'-ZrO2) transforms into cubic ZrO2 (c-ZrO2). The internal stress decreases, resulting in 90% of orthorhombic (o-ZrO2) transforming into c-ZrO2. The single sub-particle comprises both t'-ZrO2 and c-ZrO2. The residual o-ZrO2 is distributed in the sub-particle boundary. The microstructure evolution of ZrO2 results in a decrease in the strength of the bonds among the sub-particles, which promotes the ZrO2 particle disintegration and improves the thermal resistance of the coating.