Effect of relative density on cyclic oxidation resistance properties of MoSi₂

Abstract

MoSi₂ powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi₂ materials at 1 473 K was investigated by TGA, SEM and XRD. The results show that the “pesting” is not found in all materials after being oxidized for 480 h. The density has no essential relation to the “pesting”. The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage (0–1 h) and the second stage (1–480 h) nearly obey linear kinetics, but the oxidation rates are obviously different. The oxidation kinetics of MoSi₂ with higher relative density nearly follows parabolic law. The mass gains of MoSi₂ with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 10.390 and 0.135 mg/cm², respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed, which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix, showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO₂→Mo₅Si₃→MoSi₂.