Microstructure, mechanical properties and oxidation behavior of short carbon fiber reinforced ZrB2-20v/oSiC-2v/oB4C composite

Present study aims at observing the effect of short carbon fiber addition on the microstructure, mechanical properties and oxidation behavior of the ZrB2-20v/oSiC-2v/oB(4)C composite. Microstructure of the composite shows uniformly distributed SiC particles along with the occasional presence of short carbon fiber and B4C particles in the ZrB2 matrix. Carbon fiber addition leads to refinement of both ZrB2 and SiC grains. Both the flexural strength and maximum strain value of carbon fiber reinforced ZrB2-20v/oSiC-2v/oB(4)C composite is observed to be higher than those of the base i.e. ZrB2-20v/oSiC-2v/oB(4)C composite. Although the fracture toughness of the composite improves, hardness of the composite does not change significantly due to addition of carbon fiber. After the oxidation treatment in air furnace at 1600 degrees C for 2 h, the carbon fiber reinforced composite shows formation of SiO2 rich, continuous and protective top layer of about 30 mu m, ZrO2 + SiO2-middle layer of about 80-90 mu m and a relatively thin SiC depleted layer (similar to 100 mu m). On the other hand, the base composite shows the formation of a discontinuous SiO2-rich top layer of about 20-30 mu m, ZrO2 + SiO2-middle layer of about 60-70 mu m, and a thick (similar to 200 mu m) and cracked SiC depleted layer after the same oxidation treatment. Hardness deterioration is not observed beneath the oxide layer including SiC depleted region in case of carbon fiber reinforced composite, while a slight deterioration is observed in the base composite. Thermal diffusivity of the carbon fiber reinforced ZrB2-20v/oSiC-2v/oB(4)C composite is observed to be slightly lower than that of the base ZrB2-20v/oSiC-2v/oB(4)C composite.