A study of interface reaction zone in a SiC fibre/Ti-17 composite

Abstract

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.

Investigation of interface debonding behaviour in a unidirectional SiC fibre reinforced Ti-17 composite by a single fibre push-out technique

“…The interfacial RZ in this composite system was thoroughly investigated elsewhere. 56 It is found that the interface debonding occurred between fibre coating and the reaction zone. This suggests that the bond between C coating and reaction zone is the weakest compared with those formed between different layers at the interface, i.e.…”

“…The formation of the voids is related to the diffusion process controlling chemical reaction at the interface. As discussed in, 56 the carbon atoms in the carbon coating diffused across the initially formed fine-grained sublayer into the contact area to interact with the atoms migrating from the matrix into the contact area during composite fabrication. In such situation, the outflow of the carbon atoms led to the formation of voids at the interface of the carbon coating and the RZ, as shown in Figure 8.…”

On Interfacial Microstructure Evolution in an Isothermally Exposed SiC Fiber-Reinforced Ti-17 Matrix Composite

“…It has been noted that the RZ at the fiber/matrix interface is composed of three sublayers in the composites after isothermal exposure at 450, 650, 800, and 900 for up to 100 h. The fine-grained sublayer and coarse-grained sublayer are inherited from the RZ formed in the as-fabrication composite. Both remained untransformed in the process of isothermal exposure and are TiC-type titanium carbides (Fan & Zhou, 2018). Those carbides in the initially formed sublayers do not interact with the matrix since the minimum temperature for the interaction between the carbides and Ti is 1,300°C (Strashinskaya, 1971), which is much higher than the isothermal exposure temperatures.…”

“…The chemical reaction occurring during composite fabrication and isothermal exposure at 450, 650, and 800°C can be described by equation (1), which explains the formation of the TiC-type carbide, although the short-range ordered carbide can exist from TiC 0.48 to TiC 1.0 due to the variation of diffusivities of the C and Ti atoms. The reactions associated with the formation of the titanium carbide are discussed in detail elsewhere (Fan & Zhou, 2018). In brief, disordered TiC x is only stable at temperatures above 820°C, but the disordered state can exist below 720°C as a metastable state if the material is rapidly quenched (Lipatnikov et al, 1998, 2000; Zueva & Gusev, 1999; Korzhavyi et al, 2002).…”