MICROSTRUCTURAL EVOLUTION AND MICROSEGREGATION OF GAS-ATOMIZED POWDERS OF A TIAL BASED ALLOY

A range of analytical techniques, including optical and electron micro scopy, energy dispersive X-ray analysis, and X-ray diffraction were us ed to assess the extent of segregation in gas atomised Ti-48Al-2Mn-2Nb (at.-%). the secondary dendrite arm spacing was used as a measure of microsegregation in these powders. These undercooled powders were foun d to solidify as hexagonal alpha(2) dendrites, surrounded by gamma pha se segregate. Depending on the degree of undercooling experienced by a dendritic region and its composition, the hexagonal phase was found t o transform to equilibrium gamma phase by means of either a massive or a lamellar type reaction. The final relative phase distribution of th e alpha(2) and gamma phases was a function of the powder particle size . The microstructure of the hipped powder reflected the inhomogeneity inherited from the starting powder material. (C) 1996 The Institute of Materials.