Dynamic Transformation of Two-Phase Titanium Alloys in Stable and Unstable States
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The dynamic transformations of titanium alloys are compared in stable and unstable states. In an unstable state, the driving force for the transformation is given by the Gibbs energy difference associated with undercooling, and it can be derived from either enthalpy/transus temperature or solid solution thermodynamics methods. Such transformations are accelerated by deformation through the increases in the nucleation site density and the kinetics of diffusion. In a stable state, the Gibbs energy can be calculated using solid solution thermodynamics method, and it acts as the energy barrier for the dynamic transformation. The dynamic transformation is dependent on the initial thermodynamic states associated with holding conditions prior to deformation.
The authors are grateful to Dr. S. L. Semiatin of the Air Force Research Laboratory at the Wright-Patterson Air Force Base in Dayton, Ohio, US for his help with the thermodynamics. The discussions with Professor Mohammad Jahazi and Dr. Ameth Fall of Ecole de Technologie Superieure (ETS) are acknowledged with gratitude.
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