Process and bonding performance of ZrO2 thermal barrier coatings with vertical cracks by high energy plas-ma spraying
In order to prolong the service life of ZrO2 thermal barrier coatings,HS188 alloy was used as the substrate,and NiCrAIY powder(base layer,d50=106 μm)and yttria stabilized zirconia(YSZ,d50=50 μm)were employed as sprayed feeder to prepare NiCrAIY+YSZ thermal barrier coatings using high-energy plasma spraying equipment with a progressive exploration method.The microstructure of the coatings was controlled by adjusting the stand-off distance(85,95,105 and 115 mm)and air-cooling manner(rear air cooling,rear air cooling+gun cooling,front air cooling,and front air cooling+gun cooling).The bonding strength of the coatings was evaluated by the drawing method.The results indicate that under the condi-tions of long stand-off distance and low cooling rate,it is difficult for the coatings to form a vertical crack structure due to the low instantaneous heating temperature and insufficient quenching on the sample sur-face.However,when the instantaneous heating temperature reaches the critical value and the air cooling rate is excessive,un-melted spray particles exist.When the stand-off distance is 85 mm and the cooling method is front air cooling,a thermal barrier ceramic coating with vertical crack morphology was obtained on HS188 alloy.Simultaneously,it has a moderate density of vertical cracks,the highest bonding strength and the best toughness.
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