Rapidly solidified ribbons of Ti-5wt.%Al-2.9wt.%Y and Ti-5wt.%Al-7.5wt.%Th alloys (where the composition is in approximate weight percent) were prepared by the arc melt-spinning technique. These ribbons were chopped and consolidated by hot isostatic pressing at 850 °C for 3 h. The microstructures of both as-quenched alloys are characterized by a uniform dispersion of spherical dispersoids in the matrix. Isothermal annealing of these alloys at 900 °C results in the coarsening of grains and dispersoids. A strong deviation from the parabolic law in the grain growth and dispersoid coarsening is observed in the Ti-5wt.%Al-7.5wt.%Th alloy. Zener's relation for the grain growth and dispersoid coarsening appears to be operational in this case. Microhardness measurements on the isothermally treated alloys show that a significant deterioration in hardness of the 2.9wt.% Y alloy vs. almost no change in hardness of the 7.5wt.%Th alloy may be the most dramatic difference between the two alloys.
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