Toughening of plasma-sprayed ceramic coatings through fiber reinforcement and the critical bonding temperature concept

Plasma-sprayed ceramic coatings have been widely applied to different industrial fields to protect metals from wear, corrosion and high temperature. However, the intrasplat microcracking due to quenching stress and intersplat unbonded interfaces in the coatings degrade the coating performance. With the later the fully bonded splats can be achieved based on the critical bonding temperature theory. However, with the intrasplat cracking it was regarded as intrinsic feature of thermal spraying. Facing the challenge to suppress the intrasplat microcracking, in this study toughening of splats by introducing reinforcing fibers is attempted. The short refractory fibers like YSZ are introduced into the agglomerated Al2O3-TiO2 powders as typical material. The splats and coatings are deposited by plasma spraying. The fiber distribution in individual splats were examined. The microstructure and toughness of the coating were evaluated. Results show that short fibers are well aligned following the flattening direction upon droplet impact. The significant improvement in fracture toughness is observed that is attributed to the ZrO2 fiber reinforcement.