Ti–5Ta–1.8Nb: an advanced structural material for high performance application in aggressive oxidising environments

Abstract

It is well known that Ti and Zr based alloys are best suitable for oxidizing environments due to their superior corrosion resistance. This has been exploited in the development of the ternary Ti–Ta–Nb alloy, for the dissolver in a fast reactor fuel reprocessing plant, the efforts of which are summarized in the present overview. Closing of fuel cycle is a priority for the three stage nuclear power program of India, towards which, indigenous development of reprocessing technology and materials is an important milestone. Corrosion resistance of structural materials controls the operating life of the dissolver in a nuclear reprocessing plant, where the spent nuclear fuel is dissolved in highly oxidizing boiling nitric acid. A complete physical metallurgy database of the alloy has been generated to understand the various phase transformations and the resultant microstructures. Corrosion control in different phases of nitric acid is achieved through microstructural optimization and the mechanisms of corrosion are understood using a detailed study of passive oxide film. The dependence of transformation texture on the mode of deformation and the role of severe plastic deformation on mechanical properties have been elucidated. These extensive R and D efforts resulted in a complete understanding of the metallurgy the alloy, which is discussed in this overview.