Comparative Study on Tribological Behavior of Plasma-Sprayed YSZ Coatings Deposited with Different Powders

The tribological behavior of two kinds of atmospheric plasma-sprayed YSZ coatings manufactured from fused/crushed (YSZ_C) and the plasma-densified (YSZ_P-D) powders was investigated at room temperature under dry sliding conditions. It was found that the plasma-sprayed YSZ_P-D coating possessed better wear resistance than that of YSZ_C coating. The main wear mechanism of YSZ_P-D coating with better mechanical properties is wear by ductile deformation, which is manifested by the plastic deformation and formation of a protective tribolayer on the worn surface. The direct contact between the YSZ_P-D coating and the Si₃N₄ ball is prevented by the formed discontinuous tribolayer, leading to the reduction in the severity of contact, and thereby displaying good wear resistance. However, the wear mechanism is brittle deformation for YSZ_C coating. The computational simulations based on semi-analytical method reveal that higher normal stress and higher temperature rise occur at the contact interfaces between the YSZ_C coating and Si₃N₄ ball. In this case, it is easy to cause severe severity of contact by cracking, local brittle fracture and surface fatigue, and therefore resulting in severe wear.