In situ crack-healing behavior of Al2O3/SiC composite ceramics under static fatigue strength

A three-point bending (rectangular bar) specimen was made from sintered Al2O3/SiC composite ceramics and commercial Al2O3 material, upon which a semi-elliptical surface crack of 100 μm in diameter (aspect ratio ≒ 0.9) was introduced through an indentation method. The following materials were subjected to the following crack-healing treatment: Al2O3/SiC composite ceramics (under 1573 K temperature, 1 h crack-healing time) and monolithic Al2O3 (under 1373 K or 1723 K temperature, 1 h crack-healing time) designed to heal the crack samples. Monolithic Al2O3 is able to recover strength of cracked samples by heat treatment at 1723 K. The recovery was performed by the secondary sintering process. However, the cracked samples only recovered strength slightly during heat treatment at 1373 K. The incomplete strength recoveries of cracked samples were caused by the removal of tensile residual stress ahead of the crack. The Al2O3/SiC composite exhibited large crack-healing ability. The bending strength of the cracked Al2O3/SiC samples was about 180 MPa. From the crack-healing treatment, the strength recovered up to about 850 MPa. Also, crack-healed Al2O3/SiC sample exhibited a very high static limit of 600 MPa. From these test results, it can be concluded that Al2O3/SiC has excellent crack-healing ability and that crack healing is a desirable technology for the structural integrity of Al2O3/SiC.