Improvement of the Contact Strength of Al2O3/SiC by a Combination of Shot Peening and Crack-Healing

Al2O3/SiC composite ceramics with high crack-healing ability were subjected to shot peening (SP) using zirconium oxide shots with several peening pressures and shot diameters. Specimens subjected to SP were heat-treated in air to heal the surface cracks induced by SP. The residual stress, the apparent fracture toughness, and the Weibull distribution of the contact strength were investigated, revealing that the combination of SP and crack-healing is effective for increasing the contact strength and decreasing the scatter of the contact strength of Al2O3/SiC. 1. Introduction Shot peening (SP) is a procedure commonly utilized to increase the fatigue strength of metals. The compressive residual stress generated by SP prevents fatigue crack propagation. Recent studies have shown that the near-surface strength of ceramics can be improved by SP [1, 2]. Pfeiffer and Frey [1] reported that high compressive residual stress of up to more than 1？GPa could be introduced near the surface of alumina (Al2O3) and silicon nitride (Si3N4) substrates treated by SP using 650？μm tungsten carbide shots. Furthermore, Tanaka et al. [2] reported that compressive residual stress of up to 1.5？GPa was introduced near the surface of Si3N4 that was subjected to SP using 50？μm high-strength steel shots and 1100？μm tungsten carbide shots and that the compressive residual stress increased the apparent fracture toughness. Additionally, Moon et al. [3] reported that the residual stress which is introduced to Al2O3 by SP is attributed to microcracks and dislocation. Based on the results obtained in previous studies, SP treatment is a promising technique for increasing the strength of ceramics in the surface region. Strengthening the surface layer increases the contact strength of ceramic components such as bearings and cutting tools, for which higher contact strengths are desirable. However, unintentional introduction of cracks during the SP process may compromise the reliability of the ceramics components. Certain structural ceramics exhibit crack-healing ability [4–7]. Thus, if crack-healing can be combined with SP, the surface strength and reliability of ceramics can be increased. Takahashi et al. [8, 9] investigated the effects of SP and crack-healing on the contact strength of an Si3N4/SiC composite. The Si3N4/SiC was subjected to SP using 300？μm zirconium oxide (ZrO2) shots, and the contact strength of the Si3N4/SiC was reportedly increased by SP treatment [8]. It was also reported that the scatter of the contact strength in the SP specimens of the Si3N4/SiC could be improved by