Abstract
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 Nv 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.
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