The splat is the fundamental unit of thermally sprayed coatings,which has been one of the hottest issues for decades.In order to study the splat formation,an experiment was designed and conducted,in which a millimeter-size nickel metal droplet fell freely and impacted on aluminum and stainless steel substrate.The microstructural characteristics of the splat and the heat conduction and solidification processes during the flattening process have been studied numerically and experimentally.The effect of the droplet temperature,impact velocity as well as the substrate temperature was investigated.The phenomenon of substrate melting was observed after the spreading of nickel droplet,which became more pronounced when the initial substrate temperature increased.Increasing the impact velocity of droplet resulted in a decrease in the interfacial temperature between droplet and substrate.
The plasma sprayed ZrO2-7 wt%Y2O3(7YSZ)coating has been widely applied in aircraft engine as a thermal barrier coating.In this study,the duplex TBC system(MCrAlY+7YSZ)were deposited onto 304 stainless steel substrate by APS.Four principal spraying parameters during the deposition of 7YSZ coating were optimized by using orthogonal experimental design,including the stand-off distance,plasma power,preheating temperature and powder feeding rate.Their influences on the coating's microstructure,adhesion and its mechanical properties were studied and the optimized parameters were finally obtained.The results showed that the dependence of the spraying parameters on the properties of 7YSZ coating is highly correlated to the melting condition of the in-flight particles.
Li Hui,Wang Benpeng,Wei Qi,Ji Xiaojian,Li Zhuoxin College of Materials Science and Engineering,Beijing University and Technology,Beijing 100124,China
