Selection of optimum microstructure for improved corrosion resistance in a Ti-5%Ta-1.8%Nb alloy

This paper presents the results on (i) selection of microstructure with improved corrosion resistance in a Ti-5%Ta-1.8%Nb alloy and (ii) optimization of thermo-mechanical treatment to achieve the desirable structure. Ti-5%Ta-1.8%Nb is an α + β alloy and the decomposition of bcc β → α + β is found to proceed via a number of transformation modes leading to different morphological products of α and β. The distribution of isolated β particles in a matrix of equiaxed α offered superior corrosion resistance in comparison to a lamellar α  + β structure. In an attempt to obtain this desired structure, the β annealed alloy with a lamellar structure was subjected to a series of thermal and thermo-mechanical treatments. A combination of thermal and mechanical treatments was found to be essential to achieve the structure of equiaxed α with discrete β particles.