Microstructural Evolution in Hot and Cold-Rolled Ti-Nb Alloy

Abstract

Phase transformations, morphology, and crystallographic texture evolution in hot and cold-rolled Ti-25.51 wt.% Nb alloys are investigated. The experimental procedure involves synthesis of the alloy by arc melting followed by cold or hot rolling with intermediate prior and postheat treatments. Composition and phase analysis of all alloys are conducted using x-ray diffraction techniques and microstructural observations are conducted using an optical microscope. These examinations reveal that the as-melted alloy possesses large millimeter size grains with no stored strain energy and a two phase β − α′ microstructure. Direct cold rolling followed by a short homogenization leads to a β − α′′ mixture with ω precipitates. Two hour annealing before cold rolling leads to an α′ − α′′ mixture with a characteristic triangular martensitic microstructure evidencing the act of shear on formation of the phase. Hot rolling followed by a water quench results in a β − α′′ mixture, while annealing prior to hot rolling transforms the arc-melted material to a α′ − α′′ mixture. The crystallographic textures of similar microstructure mixtures in hot and cold-rolled samples are distinctively different. The analysis shows that the microstructure serves as an identifying characteristic of the processing paths and is highly dependent on the mode of processing.