High-temperature oxidation and self-healing behavior of SiC and Ni Co-dispersed into Al2O3 matrix composite

Abstract

High-temperature oxidation behavior and recovery of mechanical strength are investigated on 5 vol%Ni/Al2O3 self-healing ceramics with 1 vol% SiC co-dispersion (SiC + Ni/Al2O3). For oxidation experiment, samples were heat-treated in the temperature range of 1200–1350 °C for 24–168 h in air. For self-healing experiment, surface cracks were introduced by the Vickers indentation and then heat-treated at 1000–1300 °C for 1 and 48 h in air. The internally oxidized zone (IOZ) on SiC + Ni/Al2O3 is composed of NiAl2O4 and Al2O3 matrix. Its thickness is smaller than that of Ni/Al2O3 under the same heat-treatment conditions. The apparent activation energy on growth of IOZ for SiC + Ni/Al2O3 is approximately 680 kJ/mol, indicating that grain boundary diffusion of oxygen ion in Al2O3 is rate-controlling. Al2O3 grain boundary diffusion of oxygen ion would be suppressed by SiO2 doping via oxidation of SiC co-dispersion. Surface cracks introduced by the Vickers indentation filled with NiAl2O4. The crack disappearance rates are comparable to that of Ni/Al2O3 with Y or Si dopants. Apparent activation energy of self-healing is approximately 350 kJ/mol and its value is similar with grain boundary diffusion of Ni ions at Al2O3 matrix. Bending strengths of as-sintered and as-cracked of SiC + Ni/Al2O3 samples are 501 MPa and 114 MPa, respectively. Samples heat-treated at 1200 °C for 6 h shows bending strength up to 550 MPa, resulting in no disadvantage on the self-healing effect for SiC co-dispersion. Both of self-healing function and resistance of high-temperature internal oxidation is achieved on SiC + Ni/Al2O3.