Enhanced ablation resistance and mechanical behavior of spark plasma sintered ZrB2-SiC composites with TiC addition

The study evaluated the ablation resistance and mechanical behavior of spark plasma sintered ZrB2-25 vol% SiCTiC (5-15 vol%) composites. The addition of TiC improved ablation resistance by promoting the formation of ZrO2.TiO2 and TiO2 phases on the oxidized composites. The ZrB2-25 vol% SiC-15 vol% TiC composite exhibited the lowest mass ablation rate of 0.11 mg/s and maximum fracture toughness of 5.8 +/- 0.29 MPa.m0.5. After ablation, SiC particle pull-out, crack deflection and crack bridging were identified as the primary toughening mechanisms. The maximum microhardness of 23.01 +/- 1.18 GPa and compressive strength of 1688.2 +/- 75.5 MPa were obtained for the ZrB2-25 vol% SiC-10 vol% TiC composite, which correspond to 92.86% and 94.31% of their respective maximum values prior to ablation. Furthermore, nanoindentation studies revealed significant improvements in both elastic modulus and nanohardness with the addition of TiC due to reduction in porosity and refinement in SiC grain size. After ablation, the elastic modulus and nanohardness reduced. However, the ZrB2-25 vol% SiC-10 vol% TiC composite retained a maximum elastic modulus of 433.61 GPa and nano-hardness of 21.88 GPa. The oxidation behavior of ZrB2-SiC composites containing TiC was analyzed at 1500 degrees C for 6 hours in air. The TiC-containing composite exhibited lower mass gain, lower parabolic oxidation rate constant and a thin oxide layer compared to the ZrB2-SiC composites.