Phase separation in a ti—al—mo alloy studied by anomalous small-angle x-ray scattering a synchrotron radiation experiment

Abstract

The mode of decomposition of the ordered β₂ phase (B2) at 450°C of the alloy Ti-21·6Al-3·4Mo has been studied by transmission electron microscopy (TEM) and anomalous small-angle X-ray scattering performed at the K Ti absorption edge. TEM observations have shown that the precipitation occurs according to a two-phase system, and the α₂ spherical precipitates are embedded in a B2 matrix. In order to calculate the composition of both phases some parameters such as the Guinier radius R _G, the spherical excluded volume (or diameter D), the number of scattering precipitates per unit volume N_v have been determined by fitting the theoretical scattered intensity curves derived from a two phase model of precipitation to the experimental data. The composition of α₂ and β₂ phases is fairly constant with the ageing times considered. The plot of the ternary diagram shows that the α₂ precipitates are slightly depleted in aluminium with ageing time as compared with the B2 matrix.