Self-diagnosis function in SiC-fiber/Si3N4-matrix composite containing electrical conductors

SiC-fiber/Si3N4-matrix composites (CMC) which contained W fiber (W-f),Ti fi ber (Ti-f) or Si3N4-TiN phase ([SIN-TIN]) as an electrically conductive pha se were fabricated by hot-pressing in N-2. Electrical resistance change (De lta R) was measured in bending tests including loading-unloading and cyclic tests. The CMC-W-f showed little Delta R in deformation regions and discon tinuous Delta R at the fracture of whole material, The Delta R of the CMC-T i-f was observed in small displacement because of brittle TiN formation dur ing the hot-pressing, but residual Delta R after loading-unloading and cycl ic tests was slight in this material. The CMC-[SiN-TiN] possessed the best sensitivity of Delta R among the three kinds of materials. At unloaded stat e, the CMC-[SiN-TiN] had clearly residual Delta R, which increased obviousl y with increasing the number of cycles. These results could be qualitativel y understood by conductive pass amputation in percolation structure of TiN particles in the matrix phase of the CMC. The self-diagnosis function of fr acture detection in the CMCs would be applicable into the damage evaluation of important materials and structures.