A #beta# type titanium alloy, Ti-15V-3Cr-3Sn-3Al, shows a variety of aged microstructures depending on treatments prior to aging. When the alloy is solution treated at temperature just above the #beta# transus, precipitation during aging is sluggish and heterogeneous. Meanwhile, the alloy solution treated at high temperatures in the #beta# region exhibits very accelerated and very homogeneous precipitation. In the materials having larger grains, there is a tendency that fine and homogeneous precipitation takes place inside the #beta# grains and the precipitation free zones are formed along the #beta# grain boundaries. Such inhomogeneous microstructures can be avoided by controlling cooling rate after the solution treatment and by employing multi-step solution treatment with special heat patterns. The evolution of the above mentioned microstructures can be explained by taking the concentration of quenched-in vacancies into account, which is determined by quenching temperature, density of vacancy sinks and cooling rate, etc.
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