The interface reaction zone (RZ) in a unidirectional continuous carbon-coated SiC fibre reinforced Ti-17 titanium alloy composite is investigated. Micro-computed tomography (CT), scanning and transmission electron microscopy are employed to characterize the fibre/matrix interface. It is revealed that the interface RZ is a 400 nm thick titanium carbide (TiC) layer which is composed of two sublayers, a 60 nm thick fine-grained sublayer and an approximate 340 nm thick coarse-grained sublayer. The RZ is formed through chemical reaction between carbon coating on the SiC fibre surface and Ti, Zr and Sn in the alloy matrix. The reaction is controlled by atom diffusion occurring at the fibre/matrix interface. However, in the reaction process, Al, Cr and Mo in the matrix are rejected and piled up in front of the RZ on the matrix side. A structure model is proposed to describe the formation mechanism of the interface RZ.

The kinetics and mechanisms of interface reactions in a unidirectional continuous SiC fiber-reinforced Ti-17 matrix composite were investigated using transmission electron microscopy and scanning electron microscopy. It was found that a reaction zone (RZ) consisting of two-layered TiC-type carbide forms at the fiber/matrix interface during fabrication of the composite. After isothermal exposure at elevated temperatures, the two-layered TiC-type carbide is inherited, and a new TiC-type carbide layer forms within the RZ after exposure at temperatures lower than 900°C, while a new Ti3C2-type carbide layer forms after exposure at 900°C. It was also observed that the growth of RZ is a diffusion-controlled and temperature-dependent process, obeying the Fick's law-based parabolic relationship and the Arrhenius equation. Two material constants, the temperature-independent rate constant k0 and activation energy Q, are determined as 31.5 × 10−4µm/s1/2 and 49.9 kJ/mol, respectively.

The debonding behaviour at the fibre/matrix interface in a unidirectional continuous carbon-coated SiC fibre reinforced Ti-17 composite was investigated. Single fibre push-out testing on thin slice specimen by micro-indentation was employed to evaluate the interface debonding strength. In order to investigate interface debonding modes, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were utilised to observe the microstructure at the fibre/matrix interface region after the fibres were pushed out. It is found that the interface debonding strength is evaluated to be 108.2 MPa in the composite. The interface debonding occurs at the interface between the interface reaction zone (RZ) and the carbon coating on the fibre surface. The carbon coating/SiC fibre interface and the RZ/matrix interface remain intact after the fibre was pushed out.

Solidification behaviors of IC10 alloy with different titanium content were investigated by isothermal solidification method. Volume percentage of liquid and precipitation temperature of primary MC type carbide, eutectic and secondary γ′ phase were investigated. The results showed that with the increase of Ti content in the alloy, the liquidus, solidus and MC carbide formation temperatures decreased, on the contrary, the formation of γ+γ′ eutectic and secondary γ′ increased. For the IC10 alloy with 1.5% titanium content, it is earlier for the interdendritic pools to be divided into the parts. At this condition, melted portion of the alloy resided during isothermal process. As a result, the castability of the IC10 with 1.5% titanium is thus the lowest.