The Effect of Heat Treatments on the Microstructure of Ti-48Al-2Cr-2Nb-xW

Ti-48Al-2Cr-2Nb-xW (where x = 0, 0.5, and 1 at. %) powders were consolidated by hot isostatic pressing (HIP). The consolidated samples were solution heat treated above the a-transus followed by stepped cooling to room temperature. Selected samples were subsequently aged at 950 °C for up to 72 hours. The post-heat treatment microstructure was examined by optical and electron microscopy. It was found that increasing holding time above the a-transus generated a more homogenous microstructure. Utilizing the stepped cooling sequence, especially with a transition temperature of 1270 °C, massively transformed gamma (Ym) was diminished. Aging caused coarsening of the fully lamellar microstructure in the 0%W and 0.5%W samples while almost no coarsening occurred in the 1 % W sample. Precipitates began to form during aging in samples containing W. The precipitates at the lamellar interfaces are fine and have a needle like shape, while precipitates at the lamellar grain boundaries are coarse and circular in shape. The size and number of the precipitates depend on aging time and the level ofW content.