Abstract
Effect of shot peening on the critical stress for crack-healing of Si_3N_4/SiC composite ceramics was investigated. Shot peening was carried out on the Si_3N_4/SiC composite with a surface crack by Yittorium stabilized Zirconia beads. Peend specimens were healed at 1100 ℃ for 5 hours under tensile stress σ_<app>≤ ranging from 0 to 500 MPa. The result clearly showed that peend specimens could heal the surface crack completely under the σ_<app>≤450 MPa. Thus, critical stress of the specimens was determined to be σ^C_<app>=450 MPa. This σ^C_<app> was 2.3 times higher than that of un-peened specimen. Furthermore, the σ^C_<app> of both specimens showed the proportional relationship to bending strength of cracked specimen σ_c(σ^C_<app> ≈ 0.64σ_c). Therefore, it can be concluded that the improved σ^C_<app> of the peened specimen is due to the compressive residual stress and, consequently, increment of σ_c.
