In this research, LaPO 4 was added to the YSZ to improve the abradability behavior of the YSZ. First LaPO 4 was synthesized by reaction of La 2 O 3 and orthophosphoric acid. In order to reduce the particle size of the LaPO 4 to the suitable range of plasma spraying, the synthesized powder was milled for 15 minute. Then, LaPO 4 was added to YSZ powder in 1:9 and 1:4 proportion and were mixed with each other to produce homogeneous powder. The RSM and full factorial method was used to optimization of the plasma spraying parameters. The DOE results shown that the electric current is the most important factor in plasma spraying of the composite powders. The NiCrAlY powder and Inconel 718 were used as bond coat and substrate, respectively. The coatings were evaluated with different examinations such as, hardness, roughness, porosity, wear and high temperature oxidation tests. The X-ray analysis shown that the LaPO 4 was stable during plasma spraying process and the amount of monoclinic phase of YSZ was reduced after the spraying. The SEM images shown that the thickness of the TGO was approximately equal in the all of the coatings. The results shown, the TGO growth rate was decreased with the time. The sintering resistance of composite coatings significantly increased in comparison with the monolithic YSZ coating. The wear test results shown that the abradability behavior improved in the composite coatings and the weight loss of the alumina ball counterpart significantly reduced in the composite coatings. Keywords: Abradable coatings, Thermal barrier coatings, YSZ, LaPO 4 , Air Plasma Spray.
