Influence of microstructure on the mechanical integrity of plasma-sprayed TiO₂ splat

The TiO₂ splats with different microstructures were deposited by controlling the deposition temperature and the substrate crystalline structure, in order to investigate the effect of microstructures on the mechanical integrity of TiO₂ splat. It was revealed that the cracking of TiO₂ splat occurs by two different modes, i.e. intergranular cracking and intragranular cracking, which depend on splat microstructures. Both the morphologies and the spacing of cracks are significantly affected by the cracking mode. The area average crack spacing ranges from 5.0 to 10.4 μm with the increase of splat grain size. In addition, it was found that the coarse grain splat and especially the monocrystalline one with (110) orientation spall off the substrate, while the fine grain splat is well bonded to the substrate. The cracking modes of TiO₂ splat was discussed based on the stress-relieving mode, which is related to the accumulation and the relaxation of quenching stress.