On the development of grain growth resistant tantalum alloys

During exposure of pure Ta to temperatures up to 1800 °C pronounced grain growth combined with embrittlement becomes a major problem. Doping with elements which form nanometer to submicron sized oxide or silicide particles is an appropriate way to prevent, or at least to hamper, uncontrolled grain growth. In the present paper the effects of doping with varying combinations of Si and Y on microstructure and mechanical properties of cold-worked and annealed Ta have been investigated. For these purposes methods including small-angle neutron scattering and transmission electron microscopy as well as light-optical microscopy have been applied. Ta samples doped with Si show a higher hardness and strength than those doped with Y or made from pure Ta powder. However, the grain growth behaviour of all alloy variants is rather similar. The particle size distributions of doped Ta change significantly with varying annealing treatments as coarsening and dissolution of the prevailing particles (oxides and silicides) take place. Therefore, particles do not play a significant role in grain growth kinetics at temperatures as high as 1800 °C. However, this loss in retarding force is partially compensated for by an increased solution drag stemming from elements in solid solution.