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 fiber (Ti_f) or Si₃N₄-TiN phase ([SiN-TiN]) as an electrically conductive phase were fabricated by hot-pressing in N₂. Electrical resistance change (ΔR) was measured in bending tests including loading-unloading and cyclic tests. The CMC-W_f showed little ΔR in deformation regions and discontinuous ΔR at the fracture of whole material. The ΔR of the CMC-Ti_f was observed in small displacement because of brittle TiN formation during the hot-pressing, but residual ΔR after loading-unloading and cyclic tests was slight in this material. The CMC-[SiN-TiN] possessed the best sensitivity of ΔR among the three kinds of materials. At unloaded state, the CMC-[SiN-TiN] had clearly residual ΔR, which increased obviously with increasing the number of cycles. These results could be qualitatively understood by conductive pass amputation in percolation structure of TiN particles in the matrix phase of the CMC. The self-diagnosis function of fracture detection in the CMCs would be applicable into the damage evaluation of important materials and structures.