| Summary: | The cooling processes of hot working for TA15 titanium alloy are highly nonlinear, during which non-isothermal and non-isokinetic phase transformations often occur leading to the changes in the microstructures and mechanical properties. The existing phase transformation models, that are established based on isothermal transformations, are either difficult to reflect the real transformation process or complicated for use. Therefore, in this paper a succinct model suitable for the transformations at any cooling path was developed by separating the transformation process into a series of linear cooling steps. First, the transformation behaviors during linear cooling processes were studied by thermal expansion experiments, and then a kinetic model of the transformations at constant cooling rates was developed based on the JMAK law. Second, the additivity of the transformations during linear cooling processes was proved, and therefore the additivity rule was extended to calculate the incubation period of the transformation during non-linear cooling process. Finally, based on the crystallization model built by T. Ozawa, the new transformation model was established, and its reliability was proved by experiments.
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