Microstructural characterization of gamma-TiAl base alloy by electron probe x-ray microanalysis and electron backscatter diffraction

Electron backscatter diffraction (EBSD) and electron probe x-ray microanaly sis (EPMA) in combination with x-ray diffraction (XRD) were applied for pha se identification of the ternary precipitates and accompanying phases in Ti -49.6Al-1.9Fe alloy after heat treatment at 1400 degrees C followed by furn ace cooling. The heat treatment resulted in formation of the duplex structu re consisting of equiaxed grains of the gamma phase (AuCu type) and lamella e of the gamma and alpha(2) (Ni3Sn type). The ternary tau(2) (Mn(2)3Th(6) t ype) phase, containing 21-22 at. % Fe, was revealed on the grain boundaries of the gamma-matrix and lamellae, and is accompanied by alpha(2) precipita tes. Different morphologies of the tau(2) + alpha(2) colonies were found to differ in chemical composition, coarse particles being depleted in titaniu m, and the fine particles enriched in it. The combination of EPMA and EBSD in scanning electron microscopy proved to be very effective in local phase identification of specimens with fine multiphase structure. (C) 2000 Kluwer Academic Publishers.