Mechanism for macrostructure delamination of TC18 titanium alloy die forging and its prediction

The macrostructure of TC18 titanium alloy die forging shows delamination. By means of thermal modeling test, optical microscope(OM), micro-tensile tests and scanning electron microscope(SEM), the microstructure characteristics and mechanical properties of “cold die structure” in the near surface and “basketweave structure” in the near center were analyzed and compared. The delamination mechanism of macrostructure from surface to center of TC18 die forging after β forging and heat treatment was discussed, the process condition criterion of macrostructure delamination was put forward and the prediction model was established. The results show that after heating in the single-phase zone, the surface deformation temperature of the forging decreases (in the two-phase zone) and the deformation degree is small, which makes the crushing degree of coarse grains before deformation low, and it is difficult to form the basketweave structure, so forging surface structure exists with the characteristics of “cold die structure”, resulting in obvious delamination. In particular, the elongation corresponding to “cold die structure” is significantly reduced, which is difficult to meet the standard. With the decrease of deformation temperature (t), the critical strain value (εf) of basketweave structure increases. According to the system data of thermal modeling test, the relationship between εf and t was expressed quantitatively; Taking εf as the criterion, the finite element subroutine was established through secondary development, and the visual prediction of macrostructure delamination of forging was realized. © 2023 Central South University of Technology. All rights reserved.