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Damage behaviour and GTN parameter analysis of TC4 powder metallurgy titanium alloy during hot deformation

Liu Ronge, Wang Baoyu, Hu Shushan

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 3

art. no. e165, 2023

The damage and fracture behaviour of TC4 powder metallurgy titanium alloy were studied by isothermal uniaxial tensile tests. The results show that microcracks formed at grain boundaries, inclusions, initial pores, and adjacent pores and cracks were gathered and perpendicularly linked to the tensile direction, eventually leading to the macroscopic fracture of the material. Increasing the temperature and strain rate promotes the occurrence of dynamic recovery and subgrain merging nucleation, which leads to an increase in the fracture strain and plasticity of the material. Combined with the response surface methodology and genetic optimization algorithm, the GTN damage parameters were obtained by the reverse calibration method. The calculated flow stresses, based on the GTN damage model, are in good agreement with the experimental ones, indicating that the damage parameters can reflect the damage process of the material. In this study, the sensitivity of the damage parameters along with the influence of temperature and strain rate on them was analysed.

Microstructure and mechanical properties of TC4 titanium alloy hollow shaft formed by cross wedge rolling

Feng Pengni, Yang Cuiping, Wang Baoyu, Li Junling, Liu Ronge

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 3

737--751

Production of hollow shafts satisfying mechanical performance requirements can well meet the needs of lightweight. The purpose of this work is to investigate the effect of cross wedge rolling (CWR) process parameters on microstructure and mechanical properties of TC4 titanium alloy hollow shafts, so as to ensure the feasibility of forming TC4 titanium alloy hollow shaft by CWR. The results demonstrate that the initial deformation temperature, area reduction, wall thickness, and mandrel have significant effects on the volume fraction of primary alpha phase (fα_p), morphology of alpha phase and interface of alpha/beta phase. The decrease of the fα_p, the increase of fine secondary alpha phase content and the increase of the number of alpha/beta phase interfaces can increase the strength of TC4 alloy hollow shafts, but decrease the elongation. When the initial deformation temperature is 950 °C, the contribution of the thick secondary alpha phase is similar to that of the primary alpha phase, resulting in the decrease of strength. The strength is further improved owing to the grain refinement with the increase of area reduction to 60%. The strength decreases as the wall thickness increases owing to the non-uniform microstructure distribution, which can be improved by increasing the area reduction appropriately. The comprehensive mechanical properties of the workpiece rolled with a mandrel are evidently higher than that rolled without a mandrel. Under any forming condition in this work, every fracture surface is covered with abundant dimples and voids, showing good ductile fracture characteristics.