Formation of (α+β) Microduplex Structure in a Ti-15V-3Cr-3Sn-3Al Alloy

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The cold rolling effect of β single-phase on α precipitation behavior and the mechanical properties were studied using a Ti-15V-3Cr-3Sn-3Al metastable β alloy. The β single-phase material was prepared by heating the alloys above the β transus temperature followed by quenching in water, and subsequent aging at the (α+β) two-phase temperature after cold rolling. Cold rolling of the β single-phase had a considerable effect on the resulting (α+β) structures. Without cold rolling, preferential α precipitation occurred at the β grain boundaries, and then lath-shaped α precipitated in the β grains. When the amount of cold rolling was less than 50%, preferential precipitation of α occurred at dislocations introduced into the β grain by cold rolling, as well as the β grain boundaries. On the other hand, with an increase in the amount of cold rolling, α precipitation occurred predominantly at β subgrain boundary nodes which were formed through recovery of the deformed β single-phase during heating to the aging temperature or in the early stage of again. In heavily cold rolled specimens, an (α+β) microduplex structure, which consisted of very fine β subgrains and α particles, was obtained. Mechanical properties, such as tensile strength and elongation, were improved by the formation of the (α+β) microduplex structure.