THERMODYNAMIC ACTIVITIES AND PHASE BOUNDARIES FOR THE ALLOYS OF THE SOLID-SOLUTION OF CO IN NI3AL

The vaporization of the alloy samples of the compositions (Ni3Al)(1-x) Co-x(x = 0, 0.03, 0.06, 0.09, 0.12, or 0.15) was investigated at tempe ratures between 1326 to 1581 K by the use of Knudsen effusion mass spe ctrometry in order to obtain thermodynamic data for the solid solution gamma' phase of the type Ni3Al. The partial pressures of Al, Co, and Ni were determined over the samples investigated. Excess chemical pote ntials at a temperature of 1473 K resulted for the components in the g amma' solubility range. New results on the phase boundaries of the gam ma' solubility lobe were obtained by the analysis of quenched alloy sa mples and from the mass spectrometric studies. The results obtained ar e discussed with respect to the solubility behavior of Co in the gamma ' phase.