Transmission electron microscopy of the fibre-matrix interface in SiC-SCS-6-fibre-reinforced IMI834 alloys

Abstract

In SiC-SCS-6-fibre-reinforced IMI834 alloys, a high thermal stability of tensile properties and of the fibre-matrix interface for temperatures up to 700 °C was reported. In the present paper, the interface of these composites is investigated by analytical transmission electron microscopy in the as-processed condition and after a thermal treatment at 700 °C for 2000 h and at 800 °C for 500 h. The interface in (SiC-SCS-6)-IMI834 composites consists of two layers: the TiC reaction zone with a thickness of about 0.4 μm and a layer of a (Ti, Zr)xSiy phase with a thickness of about ∼0.1 μm. The energy-dispersive electron beam analysis of the (Ti, Zr)xSiy layer results in a (Ti, Zr)2Si phase with a Ti-to-Zr ratio of approximately 1.4. Electron beam diffraction of the (Ti, Zr)xSiy layer identifies it as S2 silicides present in near-α alloys. The thermal stability of the interface in the (SiC-SCS-6)-IMI834 composites is ensured by the continuous coating of the (Ti, Zr)xSiy phase. This is the case for a thermal treatment at temperatures up to 700 °C for 2000 h. After the treatment at 800 °C for 500 h, the thickness of the TiC reaction zone is increased, gaps in the (Ti, Zr)xSiy layer appear, titanium carbide grows further into the titanium matrix and the thermal stability of the interface is lost.