Study on microstructure evolution and spheroidization mechanism of TC11 titanium alloy during ACDR and upsetting forming

In recent years, the use of “near-net forming” to manufacture key components of aeroengines has become a mainstream development direction. In this paper, “near-net forming” of rotating parts such as disks and shafts is realized by using axial closed die rolling (ACDR) deformation technology. Numerical simulation and experimentation research were utilized to compare the plastic deformation characteristics and microstructure evolution of TC11 disc component forming by upsetting and ACDR forming, including strain distribution, temperature distribution, and microstructure evolution mechanisms. The FEM results revealed that during the ACDR process, the equivalent strain exhibits a radial distribution pattern with the center of contact area between the billet and upper die. The top surface of the billet was located in the severe plastic deformation zone and had better microstructure uniformity as a whole. In addition, ACDR forming enables continuous “near-net forming” at relatively low loads. The experimental results illustrated that ACDR formation is characterized by three types of deformation: radial tension, circumferential torsion, and axial compression, and at the same time, the overall strain is higher. As a result, the initial α size in the core was finer and exhibited an equiaxial shape, and the remaining areas of the grain were relatively fine and more uniformly distributed. The ACDR forming process can obtain a uniform and refined TC11 microstructure more efficiently. The TEM morphology observation of the ACDR specimens revealed that the lamella α-phase was bent, twisted, and fractured under the combined action of axial and shear stresses. The spheroidization models are primarily the globularization model of shearing lamellar structure the grain boundary splitting model, the termination migration globularization model, and the globularization model of Rayleigh instability.