High-temperature microstructure evolution and thermal stability of SiCf/Ti60 composites

Abstract

The microstructure evolution and thermal stability of continuous SiC fiber-reinforced Ti60 (SiCf/Ti60) composites at elevated temperatures have not been reported. The objective of this study was to conduct thermal exposure experiments of SiCf/Ti60 composites at 400 °C / 100 h, 600 °C / 100 h, and 800 °C / 100 h. The aim was to compare the interfacial and matrix microstructures under hot isostatic pressure (HIP) conditions and to assess their thermal stability. The results show that SiCf/Ti60 composites have excellent long-term thermal stability at 600 °C thermal exposure, short-term thermal stability at 800 °C thermal exposure and the thickness of the reaction layer (RL) increases to ∼1.27 μm. From HIP to 800 °C thermal exposure, RL changes from fine-grained TiC ║ discontinuous silicides ║ coarse-grained TiC to fine-grained TiC ║ near-continuous silicides ║ medium-grained TiC ║ coarse-grained TiC. Large-sized β-Ti and S2 silicides precipitated in the matrix at 800 ℃ thermal exposure, where β-Ti and α-Ti followed the Burgers orientation relationship (BOR), and the S2 exhibited a multitude of orientation relationships with both β-Ti and α-Ti. Furthermore, it was demonstrated that thermal exposure resulted in a reduction in the dislocation density of the matrix. In particular, thermal exposure at 800 °C led to a decrease in the dislocation density of the matrix by ∼47 %. This observation provided a novel approach for the reduction of crystal defects in the matrix and the enhancement of the properties of SiCf/Ti composites.