Nanostructural evolution of fibre-matrix interface of Ti6Al4V-SiCf composite

The Ti6Al4V-SiCf composite, consisting of Ti6Al4V matrix reinforced by unidirectional SiC fibres (see Fig. 1), is a very promising material for applications in aeronautical engines. This composite was fabricated at the C.S.M. laboratories by hot isostatic pressing of Ti6Al4V sheets alternated with SiC fibre layers coated by 3 m thick carbon film [1]. The samples of this material have been submitted to an extensive microstructural, microchemical and mechanical characterization in as-fabricated condition and after prolonged heat treatments with exposure time up to 1,000 h at temperatures ranging from 400 to 600 °C. This temperature range corresponds to the medium working temperatures of the components for application in aeronautical turbines. In Ti-based composites, reinforced with unidirectional fibres, namely the interface between the fibres and metallic matrix is the zone, where diffusion phenomena and chemical reactions may occur leading to material’s instability and rupture. For this reason, numerous experimental and theoretical studies (e.g. [2-4]) have been devoted to reaction kinetics at the interface. The nanostructural evolution of fibre-matrix interface in the composite during prolonged heat treatments has been investigated by means of high-temperature X-ray diffraction (HT-XRD), energy dispersion spectrometry (EDS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) combined with Ar ion sputtering [5]. The analyses have been performed on different zones of the samples: fibre, fibre-carbon interface, carbon, carbon-matrix interface and matrix. In order to extend the analysis area, the sample surfaces, forming a small angle (about 2 degrees) with fibres axis, have been prepared by mechanical polishing (Fig. 2)