2006 Volume 47 Issue 7 Pages 1649-1653
Plasma sprayed alumina coating has demonstrated great potential in improving the loading capacity and service life of engineering equipments, while the low thermal conductivity limits its application when high heat exchange efficiency is required. In this paper AlN with different proportion was added into the feedstock powder of Al2O3, and a series of AlN/Al2O3 composite coatings was deposited on mild steel substrate by plasma spray. Its mechanical properties were studied and thermal conductivity was measured by Transient Plane Source (TPS) method. XRD and EDS analysis revealed that most of the Al2O3 in composite coating underwent phase transformation from α phase to metastable γ phase during plasma spraying, and the mass fraction of AlN was decreased comparing with the chemical composition of feedstock powders. With the increase of AlN proportion, the microhardness reduced from 847 Hv of pure Al2O3 coating to 685 Hv when the mass fraction of AlN was 0.47, companying with the bond strength decreased from 27.4 to 21.3 MPa, and the corrosion rate decreased by half. The addition of AlN resulted in the increase of thermal conductivity by several times comparing with the original Al2O3 coating.