Insight into the effect of Ti substitutions on the static oxidation behavior of (Hf,Ti)C at 2500 ​°C

Hf-based carbides are highly desirable candidate materials for oxidizing environments above 2000 ​°C. However, the static oxidation behavior at their potential service temperatures remains unclear. To fill this gap, the static oxidation behavior of (Hf, Ti)C and the effect of Ti substitutions were investigated in air at 2500 ​°C under an oxygen partial pressure of 4.2 ​kPa. After oxidation for 2000 ​s, the thickness of the oxide layer on the surface of (Hf, Ti)C bulk ceramic is reduced by 62.29 ​% compared with that on the HfC monocarbide surface. The dramatic improvement in oxidation resistance is attributed to the unique oxide layer structure consisting of various crystalline oxycarbides, HfO₂, and carbon. The Ti-rich oxycarbide ((Ti, Hf)C_xO_y) dispersed within HfO₂ formed the major structure of the oxide layer. A coherent boundary with lattice distortion existed at the HfO₂/(Ti, Hf)C_xO_y interface along the (111) crystal plane direction, which served as an effective oxygen diffusion barrier. The Hf-rich oxycarbide ((Hf, Ti)C_xO_y) together with (Ti, Hf)C_xO_y, HfO₂, and precipitated carbon constituted a dense transition layer, ensuring favorable bonding between the oxide layer and the matrix. The Ti content affects the oxidation resistance of (Hf, Ti)C by determining the oxide layer's phase distribution and integrity.