The oxidation effects on microstructure and mechanical behavior of the Csf/α- Al2O3 composites at 1000 °C

Abstract Effects of oxidation on fracture behavior, microstructure and mechanical properties of the short carbon fiber reinforced α-Al 2 O 3 composites (C sf /α-Al 2 O 3 ) were studied under 1000 °C in ambient atmosphere for up to 40 h. The C sf /α-Al 2 O 3 composites with carbon fiber content of 5 vol% (denoted as C sf 5) exhibit catastrophic fracture mode before and after oxidation. The C sf 10 sample that has a pseudo-plastic fracture behavior exhibits catastrophic failure after only 0.5 h of oxidation. The retention strength of C sf /α-Al 2 O 3 composites, apparently decreased with the increasing of oxidation time, is strongly influenced by the content of residual carbon fiber. After oxidation at 1000 °C for 0.5 h, the retention strengths of C sf 5 and C sf 10 composites are 300 MPa and 222 MPa, which are 89% and 90% of the original strength respectively. After 2 h of oxidation, the retention strengths of C sf 5 and C sf 10 are 242 MPa and 185 MPa, which are 72% and 69% of the original strength respectively. Oxidation process significantly affects the matrix morphology of C sf /α-Al 2 O 3 . A large amount of small grain appears and characterizes the matrices of C sf 5 and C sf 10 samples after 40 h of oxidation. The substrate grain refinement is ascribed to a process of carbothermal reduction nitridation reaction of Al 2 O 3 .