The Effects of Water Addition on the Color and Crystalline Phase of Y2O3 Coatings Fabricated by Plasma Suspension Spray

The effects of water addition on Y 2 O 3 coatings or thick films prepared by plasma suspension spray (SPS) have been investigated. Water addition in suspension media was found to be effective to control the color of a Y 2 O 3 coating prepared by SPS. The color changed with water addition at the shortest stand-off distance of 50 mm even if samples had the same crystalline phase. Change was not correlated with fragmentation behavior of liquid suspension inside the plasma jet. Water content over 50 vol% was found to produce unmelted particles, indicating that water suppressed heat transfer to the particles. However, plasma jet temperature was not affected. Instead, the coating fabricated with water addition has higher oxygen and lower carbon content compared to these characteristics of the coating without water addition. This was attributed to the retarded complete evaporation of liquid media from the suspension droplet, resulting in inhibition of excessive heating and evaporation of the molten Y 2 O 3 droplet. In this regard, crystalline phase development with respect to stand-off distance and water addition was discussed.