Fabrication and mechanical behavior of ZrB2 strengthened SiCf/SiC composites prepared by hybrid processing route

摘要

A SiC fiber-reinforced composite containing a SiC-ZrB2 mixed matrix (SiCf/(SiC-ZrB2)) with high density and enhanced mechanical properties was fabricated. ZrB2 at 5 or 40 vol% was added to a (SiC + C) slurry to be infiltrated into the voids of 2D woven Tyranno'm-SA grade-3 fabrics by electrophoretic deposition. Subsequent hot pressing at 1300 degrees C and 10 MPa for 1 h, followed by liquid silicon infiltration (LSI) at 1600 degrees C for 5 h in an Ar atmosphere resulted in the formation of the reaction-bonded SiC matrix, which revealed a composite density close to 97%. SiCf/(SiC-ZrB2) having open porosities of 0.2-0.6% showed peak strengths of 398 and 320 MPa for 5 and 40 vol% ZrB2 addition, respectively. The large mismatch in the coefficient of thermal expansion and Young's modulus between the SiC and ZrB2 phases was attributed to a reverse trend in the strength of composites. Brittle behavior of the composites in flexure can be explained by the strong bonding between the matrix and fibers formed by the reaction of interphase with molten Si during LSI. Strength retention after oxidation at 1000 and 1400 degrees C for 2 h was also compared in terms of ZrB2 amount contained in the composites.