Mechanism for the Macrostructure Coarse Grain of TB6 Titanium Alloy Die Forging and Its Prediction

doi:10.3901/JME.2024.08.121

Abstract

Abstract: The local area of macrostructure of TB6 titanium alloy die forging shows the flaw of coarse grain after deformation and annealing in two-phase region. By means of thermal modeling test, optical microscope(OM), micro-tensile tests and scanning electron microscope(SEM), electron black-scattered diffraction(EBSD), the microstructure characteristics and mechanical properties of "the area of macrostructure coarse grain" and "the area of macrostructure fine grain" are analyzed and compared, the formation mechanism of macrostructure coarse grain is discussed, the process condition criterion of the appearance of the macrostructure coarse grain is put forward and the prediction model is established. The results reveal that the macrostructure coarse grain is mainly distributed in the area of violent metal flow with low deformation temperature and large deformation degree. Compared with fine-grained materials, coarse-grained materials reduce the yield strength, but increase the elongation and tensile strength. After heating in the two-phase zone, the surface deformation temperature of the forging decreases during transportation, which leads to uneven temperature in the surface area. At large deformation rate, the softening degree of surface arc region is quite different, and partial dynamic recrystallization is easy to occur, resulting in dynamic recrystallized grains with large grain boundary angle(β phase). After annealing, the dynamic recrystallized grains merge the static recrystallized grains with small grain boundary angle around through grain boundary migration to form coarse grains. With the deformation temperature (T) decreases and the strain (ε) increases, the macrostructure coarse grains appear more easily when the strain (ε) does not exceed the critical value. The relationship between ε_f and T is expressed quantitatively; Taking ε_f as the criterion, the finite element subroutine is established through secondary development, and the visual prediction of macrostructure coarse grain of forging is realized.

Key words: TB6 titanium alloy, macrostructure coarse grain, formation mechanism, recrystallization, visualisation model

CLC Number:

TG146

ZHANG Yusen, CHEN Lei, LIU Shengjie, HU Junhua, ZHANG Qifei, CUI Mingliang, HU Jianliang, JIN Miao. Mechanism for the Macrostructure Coarse Grain of TB6 Titanium Alloy Die Forging and Its Prediction[J]. Journal of Mechanical Engineering, 2024, 60(8): 121-131.

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