The effects of CVD SiC interphase on mechanical properties of KD-1 SiC fiber reinforced aluminum phosphate composites

The KD-1 SiC fiber reinforced aluminum phosphate (SiC/Al(PO3)3) composites were fabricated by the method of vacuum infiltration and heat treatment using Al(H2PO4)3 as precursor. The major phases of matrix are cubic Al(PO3)3 and monoclinic Al2P6O18. The KD-1 SiC fibers are degraded by the water vapor released from Al(H2PO4)3. In order to protect the KD-1 SiC fibers, the CVD SiC are coated on fibers before infiltration of aluminum phosphate. It was found that the flexural strength of composites enhances as increasing of CVD SiC thickness, but the fracture behavior exhibits brittle rupture when the interphase is too thick. The thickness of CVD SiC interphase is optimized as 1.5 μm from the mechanical properties point of view. In addition, the effects of heat treatment in air on mechanical properties of SiC/Al(PO3)3 composites were researched. The retentions of flexural strength of SiC/Al(PO3)3 composites with 1.5 μm CVD SiC interphase after heat treatment in air at 800, 900, 1000 °C for 6 h are 90.3%, 70.9% and 67.20%, respectively.