Study On The Ni/Diatomite Sealing Coatings Prepared By Suspension Plasma Spraying

Seal coating is one of the important measures to improve engine efficiency. With thegrowing development of aviation technology and the dwindling of energy, the engines of highesteem，high efficiency and low oil consumption, become more and more in demand. In orderto adapt to this demand, the research and development of new seal coatings technology arevery necessary. Suspension plasma spray (SPS) technology is a new spraying method. Thispaper, using nickel, diatomite, and supporting materials as raw material, prepares Ni/diatomiteseal coatings by SPS technology. On the basis of optimization of the process parameters,suspension properties and coating structures and properties are studied.The results show that, when the milling time is24h, and1%vol of the dispersing agent isadded, the size of suspended particles can advance to the micron, deep submicron or evennanometer level after the ball milling process. These particles are flake-like, and the theagglomerate phenomena is not obvious. There is no changes of elements and phases in theball milling process. And, it is proved by the viscosity test, the sediment test, thetransportation test and the atomization test, that the suspension is stable and is with goodfluidity and atomization.The coating of more than1.5mm thick can be prepared by SPS method. Also, thecoatings are composed by full melted regions, partial melted regions and unmelted regions. Itis proved by XRD and EDS that the phases of the coating comprise a lot of Ni and SiO2, andlittle NiO. The coatings are also porous. The spraying efficiency decreases with increasingSiO2content. The surface hardness of the coating is between30to50, which can meet thecriteria of the sealing coating. Also, the coating has good thermal shock performance, and canbear more than40times of heat cycle shock.The coating structure is affected by SPS parameters. The spraying power acts on the melting of the droplets; the feeding pressure acts on the degree of atomization and the amountof the droplets which are shot into the plasma flame; and spraying distance acts on the heatingtime which affects the melting of the particle and the impact between particle and substrate;The velocity of the movement of the spraying gun acts on the distribution of porosity and thecracks in coatings.