Stress-induced martensitic transformation in titanium alloys

When the temperature is higher than MS point, the chemical driving force decreases with the increase of temperature, and the critical stress increases with the increase of temperature. In the process of stress-induced martensitic transformation, the external stress is equivalent to changing the thermodynamic conditions of the system, and the work of the stress on the system is the same as that of the chemical driving force in the system.
Therefore, the presence of applied stress is equivalent to increasing the temperature. With the increase of applied stress, the critical stress of stress-induced martensite gradually increases, and this stage is stress-induced martensite. When the temperature rises to, the critical stress of stress-induced martensitic transformation is equal to the yield strength of the parent phase. As the temperature continues to rise, the critical stress required for martensitic transformation is already greater than the yield strength of the parent phase, and the material matrix begins to undergo plastic deformation, followed by martensitic transformation. At this time, the critical stress required for martensitic transformation is less than the actual applied stress value, which is because the plastic deformation of the parent phase reduces the critical stress value. The corresponding phase is strain-induced martensitic transformation.
The orientation of heat-induced martensite is chaotic and disordered. Unlike heat-induced martensite transformation, the orientation of stress-induced martensite is generally single. This is because the applied stress is directional, so it is also selective in the process of martensite shear induced by stress