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 Ti_3AlC_2 and Ti_3SiC_2 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 Ti_3AlC_2 and Ti_3SiC_2 lamellar ceramics were prepared from Ti,Al(Si) and C powders by reactive hot pressing in vacuum at 1450℃for 1.5 h under 30 MPa.Their phase constitution, mechanical characterization and thermal properties were investigated.In addition,plasma-sprayed monolayer ZrO_2 thermal barrier coatings free of metallic transition layer were prepared on the two ceramic substrates.The purity of the Ti_3AlC_2 and Ti_3SiC_2 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 Ti_3AlC_2 and Ti_3SiC_2,respectively.They took a respective average value of 8.77×10~(-6) and 9.14×10~(-6)/℃for the coefficient of thermal expansion(CTE) without remarkable temperature dependence between 25 and 1000℃.Furthermore,the coatings contributed to a more than 60%decrease in the high temperature thermal conductivity compared to the two matrices.In general, Ti_3AlC_2 and ZrO_2-coated Ti_3AlC_2 displayed superior comprehensive properties to Ti_3SiC_2 and ZrO_2- coated Ti_3SiC_2.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℃for Ti_3AlC_2 and Ti_3SiC_2 substrate,respectively.