Microstructure and phase relations in a powder-processed Ti-22Al-12Nb alloy

A systematic investigation was undertaken to compare the effect of processing on the phase relations and microstructure of 66Ti-22Al-12Nb (in at. pct) alloy. The alloy was processed by three different routes: (1) cold pressing (CP) followed by reaction sintering; (2) CP followed by hot pressing (HP) followed by sintering; and (3) arc melting (AM), hydride-dehydride processing to make the alloy powder followed by cold isostatic pressing and then sintering. The samples were analyzed by X-ray diffraction (XRD); optical microscopy, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS), and electron microprobe analysis (EPMA). The analyses showed that all the processing methods have resulted in the same phases, but the AM route resulted in an equiaxed microstructure, whereas the other two methods resulted in a lamellar microstructure. This refinement in microstructure was attributed to the hydride-dehydride processing step of the AM route.