Influence of heat treatment temperature on self-healing effect of fe particle/Mullite ceramic composites

Self-healing function in ceramic-based composites is one of unique characteristics to improve the strength reliability. In this study, such a strength recovery phenomenon of 5 vol% Fe particle/2 mol% Y₂O₃/Mullite composite was investigated at various heat treatment temperatures. Vickers indentation were conducted with dense rectangular samples. Samples were heat treated at 700 -1000°C for 1 h in air or Ar-3%H₂ atmosphere and then 3-point bending test was carried out at room temperature. Peaks of hematite were identified in the XRD profiles of the samples after heat treatment in air. Surface cracks mostly disappeared due to formation of the oxidation product, i.e., particle-like hematite formed by the heat treatment at 900°C in air for 1 h. Further, needle-like hematite formed and penetrated into the sample surface by the heat treatment at 1000°C. While, oxide formation was not observed for the sample treated in Ar-3%H₂ atmosphere. The bending strengths of the as-polished and as-cracked samples were 334 and 99 MPa, respectively. Recovery rate is increased with increasing heat treatment temperature up to 900°C. Heat-treatment at 900°C for 1 h resulted in a recovery of the bending strength up to 262 MPa. While, bending strengths of the samples treated at 1000°C for 1 h air was 204 MPa. It appears that needle like hematite degrades mechanical properties of the samples. Bending strengths of the samples treated at 900°C for 1 h air was 112 MPa as well as as-cracked sample due to no formation of oxidation product.