Abstract
Prepared multiphase ceramic coatings on the surface of aluminum alloy is a way to improve wear resistance of aluminum alloy. In this work, the mixed powders were prepared by mechanical alloying ,and the Al2O3-TiB2 composite coating was obtained by plasma spraying.The major excellences exist in small ceramic phase particles, evenly distributed and high bonding strength in coating.
In this dissertation, characteristics with spraying powder ,prepared process and formation mechanism of Al2O3-TiB2 composite coating were studied.The influences of mechanical alloying and spraying temperature on the phase constituent and microstructure of the composite were analyzed by X-ray diffractometry(XRD) and scanning electron microscopy(SEM).The oxygen-acetylene flame spraying (low temperature) and plasma spraying (high-temperature conditions) were used to obtained coatings because mixture melting points of powders were different. The affect of spray temperature, spray distance and binder for microstructures and properties of the preparated coating was analysed. From above mentioned experimental results the fallowing can be concluded:
There are only Al,TiO2,B2O and B2O3 phases in coating was obtained with unmilled mixed powder by flame spraying.Therefore,no reaction has been happen in sparying.It is found that coating obtained with milled powder by flame spraying and plasma spraying results in an Al2O3 and TiB2 phase,which was confirmed by XRD measurements.The coating obtained by flame spraying has little hard particles of Al2O3 and TiB2,and the bonding strength of coating obtained by plasma spraying was low.The spray reactions of mixed powder had take place during flight course, and the best spray distance was 350mm.Through the analysis of SEM，coating without binder was discontinuous and difference density; coating with 20% binder has a good bonding effect and grains of Al2O3 and TiB2 well-distributed. The maximum microhardness of coating was 1300 HV0.1。
Keywords: composite coating；mechanical alloying；reactive spraying；binder
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