Effect of Si/Ta Ratio on the Microstructure and High Temperature Anti-Oxidation Property of SiC/TaSi2 Coating for Carbon/Carbon Composites

A SiC/TaSi2 multilayer oxidation protective coating for carbon/carbon (C/C) composites was prepared by pack cementation. Effect of the content of Si and Ta in the second-step pack powders on the microstructure and high temperature anti-oxidation property of the multi-coating was studied by XRD, SEM and isothermal oxidation test. The results show that with the ratio of Si and Ta decreasing, the as-received multi-coating thickness first increases and then decreases. The multi-coating prepared at the ratio of 5:1 of Si and Ta has a thicker, denser structure and higher content of TaSi2 than those prepared at the ratio of 6:1, 4:1 and 3:1. After 241.8 h oxidation in air at 1500 degrees C and thermal cycling between 1500 degrees C and room temperature for 18 times, the weight loss of the coated specimen was only 1.04%, implying that the multi-coating prepared at the ratio of 5:1 of Si and Ta has excellent oxidation protective ability and thermal shock resistance. The oxidation protective failure of the SiC/TaSi2 coating was attributed to the formation of some penetrable cracks in the coating after a long time of oxidation.