Obtaining high-performance SiC_f/SiC by combined CVI and PIP processes with moderately enhanced BN weak interphase

2D SiC_f/SiC composites with excellent mechanical properties were successfully prepared by hybrid chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) processes, which consisted of depositing a protective layer of CVI-SiC on the fiber preform with BN interphase, followed by cyclic precursor infiltration and pyrolysis until densification. The volume ratio of CVI-SiC matrix to PIP-SiC matrix of 3:1 showed the most desirable mechanical properties with the highest flexural strength of 720.1 ± 32.1 MPa and fracture toughness of 34.2 ± 1.1 MPa·m^1/2. The enhancement of strength was attributed to the efficient filling of pores achieved by the two hybrid processes, with the best performing sample density of 2.52 g/cm³. The synergistic increase in toughness was achieved by controlling the state of internal stress and further increasing the interfacial shear strength. The fiber Push-in tests showed that the interfacial shear strength increases with the increasing of the CVI-SiC content, and finally a weak BN interphase with a moderate enhancement effect was obtained with an interfacial shear strength of 34.1 ± 5.3 MPa. The results illustrated that the combined CVI and PIP processes with adjustable composition and stress were able to provide new design ideas for improving the mechanical properties of SiC_f/SiC.