Microstructure and high temperature mechanical properties of mechanically alloyed Nb3Al-based materials

The microstructure and high temperature mechanical properties of mechanically alloyed Nb3Al-based materials have been investigated. The results for four binary Nb–Al and three ternary Nb–Al–V materials are presented. The microstructure of the present alloys consists of four phases: a disordered Nb solid solution, the Nb3Al and Nb2Al ordered phases and aluminum oxide dispersoids. All alloys exhibit high strength at 800 °C, but only ternary alloys retain the strength up to at least 1100 °C. The presence of vanadium, with its atomic diameter significantly smaller than those of Nb and Al, is postulated to lead to the solid solution strengthening. In the ternary alloy Nb–15 at.% Al–20 at.% V consolidated at 1500 °C the creep rates are significantly lower (one to two orders of magnitude) than in all other alloys investigated in the present study because of the absence of the Nb2Al phase in its microstructure. Creep rate dependence on temperature in the present alloys is controlled by the diffusivity of Nb and Al atoms (and V atoms in the ternary alloys) in the ordered Nb3Al phase and the creep mechanism is diffusion-assisted dislocation creep.