Preparation and microstructure of in situ particle reinforced titanium matrix alloy

Ti–6Al/TiC, Ti–6Al/TiB and Ti–6Al/TiC+TiB have been manufactured by an in situ method. X-ray diffraction (XRD), optical microscopy and scanning electron microscopy (SEM) have been used to identify the phases and observe the morphologies and distribution characteristics of TiC and TiB with the change of the alloy composition. In Ti–6Al–(0.4–2.0)C alloys, TiC appears mainly to be rod-like shape in low C content alloys and coarse dendritic shape in higher C content alloys, respectively. The rod-like shape TiC has a tendency to segregate at the grain boundary. It was also shown that the Al content has great influence on the phase constitute and the reinforcement morphology. In Ti–6Al–(0.3–1.2)B alloys, TiB was formed as reinforcement and the in situ TiB is mainly fibrous. But in higher B content alloys, some hollow TiB fibres were also formed. The distribution and the size of TiB are very sensitive to the cooling rate. In TiC+TiB reinforced composites, TiC and TiB still remain dendritic and fibrous, respectively. However, the coexistence of TiC and TiB slightly reduces the scale of the reinforcements. The microhardness was found to have little dependence on the morphology of reinforcements.