Spheroidization Behavior and Hardening Mechanism of the Lath Ti2AlNb Alloy During Multi-directional Isothermal Forging

Multidirectional isothermal forging ( MIF) experiments of Ti2AlNb alloy was carried at 800 degrees C. The microstructure evolution and hardness of the alloy under different deformation cycles were quantitatively analyzed by SEM, XRD, EBSD and hardness testing. The dynamic spheroidization behavior of the lath O and alloy hardening mechanism was revealed. The results show that as the number of deformation cycles increases, the initial coarse lath O has undergone two refinement mechanisms, namely dynamic mechanical breaking and dynamic recrystallization. The globalization of the lath mainly occurs in 3 cycles deformation process. The dynamic spheroidization process is accompanied by four deformation behaviors: bending, kinking, shearing and grain tearing. The mechanism of the latter two types of deformation can be summarized as: O/O phase boundary separation, penetration of B2 phase, O phase separation and O phase spheroidization. The initial lath O phase is refined to 1.3 mu m equiaxed structure, and the percentages of fine equiaxed O phase is as high as 68.84% after 3 cycles of MIF. At this time, the hardness of the alloy is 103.55HV ( 1014.79 MPa) higher than that of the initial sample, and the contribution of grain boundary hardening mechanism is 64%.