Increase in critical stress for crack-healing of Si3N4/SiC ceramics by shot peening

The effects of shot peening on the critical stress for crack-healing of Si3N4/SiC composite ceramics were investigated. Shot peening was carried out on a Si3N4/SiC composite with a surface crack by using yttrium-stabilized zirconia beads. Shotpeened specimens were crack-healed at 1100 °C for 5 h under a tensile stress (?app) in the range 0\u96500 MPa. The results clearly showed that the surface cracks in shotpeened specimens were healed completely for ?app ? 450 MPa. Thus, the critical stress for crack-healing (?C app) was determined to be 450 MPa. This ?C app value was 2.3 times that for an unpeened specimen. Furthermore, the ?C app values for both specimens showed a proportional relationship with the bending strength of the cracked specimen ?c (?C app ? 0.64?c). Therefore, it can be concluded that the increase in ?C app of the peened specimen is due to the compressive residual stress and the consequently increase in ?c