Kinetics and mechanisms of chemical reactions at the unidirectional continuous SiC fibre/Ti-17 composite interfaces

摘要

Unidirectional continuous fibre reinforced titanium matrix composites have gained significant attractiveness for aerospace applications since they were initially proposed in 1960s due to their high specific strength, stiffness and corrosion resistance coupled with the possibility of marked weight reductions. Significant research has been conducted on various aspects about the materials, especially in the area of fibre-matrix interface which plays a critical role in the macroscopic mechanical performance of the materials. In this paper, the kinetics and mechanisms of chemical reactions at the unidirectional continuous SiC fibre/C/Ti-17 matrix interfaces have been investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) on as-fabricated and isothermally-exposed composites. It is found that a reaction zone (RZ) composed of two-layered TiC-type carbides formed at the interface during material fabrication. After the material is isothermally exposed at elevated temperatures, the two-layered RZ is inherited from the as-fabricated composite, and a new TiC-type carbide layer forms within the RZ upon the isothermal exposure at temperatures lower than 900°C while a Ti_3C_2-type carbide layer forms after 900°C exposure. The interface stability is well maintained even though the RZ grows obviously in thickness after the material is isothermally exposed at 900°C for up to 100h. The RZ growth is a diffusion-controlled and temperature dependent process, obeying the Fick's-law based parabolic relationship and Arrhenius equation. Two material constants, temperature independent rate constant k_0 and the activation energy Q, are determined as 31.5×10~(-4) μm/s~(1/2) and 49.9kJ/mol respectively.