PROPERTIES OF Ti3XC2(X=Al, Si) WITH PLASMA SPRAYED ZrO2 THERMAL BARRIER COATING

There has been a great interest in the synthesis and characterization of Ti3AlC2 and Ti3SiC2 lamellar ceramics due to their striking combination of merits of both metals and ceramics, such as good high-temperature strength, excellent oxidation resistance. In this study, dense and high purity polycrystalline Ti3AlC2 and Ti3SiC2 lamellar ceramics were prepared from Ti, Al(Si) and C powders by reactive hot pressing in vacuum at 1450 degrees C for 1.5 h under 30 MPa. Their phase constitution, mechanical characterization and thermal properties were investigated. In addition, plasma-sprayed monoloyer ZrO2 thermal barrier coatings free of metallic transition layer were prepared on the two ceramic substrates. The purity of the Ti3AlC2 and Ti3SiC2 were 91.5% and 90.3%, and the main impurity was TiC. The flexural strength and fracture toughness were 536 MPa, 7.8 MPa.m(1/2) and 457 MPa, 6.8 MPa.m(1/2) for Ti3AlC2 and Ti3SiC2, respectively. They took a respective average value of 8.77x10(-6) and 9.14x10(-6)/degrees C for the coefficient of thermal expansion (CTE) without remarkable temperature dependence between 25 and 1000 degrees C. Furthermore, the coatings contributed to a more than 60% decrease in the high temperature thermal conductivity compared to the two matrices. In general, Ti3AlC2 and ZrO2-coated Ti3AlC2 displayed superior comprehensive properties to Ti3SiC2 and ZrO2-coated Ti3SiC2. The temperature differences between the outside surface and the coating/matrix interfaces created by the thermal barrier coating were calculated to be 341 and 358 degrees C for Ti3AlC2 and Ti3SiC2 substrate, respectively.