Thermomechanical response of 3D laser-deposited Ti–6Al–4V alloy over a wide range of strain rates and temperatures

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2015-10, Vol.647, p.34-42
• Main Authors: Li, Peng-Hui, Guo, Wei-Guo, Huang, Wei-Dong, Su, Yu, Lin, Xin, Yuan, Kang-Bo
• Format: Article
• Language: English
• Subjects: 3D laser deposition additive manufacturing; Alloy development; Fracture mechanics; High strain rate; Laser deposition; Microstructure; Plastic flow; Scanning electron microscopy; Split-Hopkinson bar technology; Three dimensional; Titanium base alloys; Ti–6Al–4V
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2015.08.043

To understand and evaluate the thermomechanical property of Ti–6Al–4V alloy prepared by the 3D laser deposition technology, an uniaxial compression test was performed on cylindrical samples using an electronic universal testing machine and enhanced Hopkinson technique, over the range of strain rate from 0.001/s to 5000/s, and at initial temperatures from the room temperature to 1173K. The microstructure of the undeformed and deformed samples was examined through optical microscopy and the use of scanning electron microscope (SEM). The experimental results show the followings: (1) the anisotropy of the mechanical property of this alloy is not significant despite the visible stratification at the exterior surfaces; (2) initial defects, such as the initial voids and lack of fusion, are found in the microstructure and in the crack surfaces of the deformed samples, and they are considered as a major source of crack initiation and propagation; (3) adiabatic shear bands and shearing can easily develop at all selected temperatures for samples under compression; (4) the yield and ultimate strengths of this laser-deposited Ti–6Al–4V alloy are both lower than those of the Ti–6Al–4V alloy prepared by forging and electron beam melting, whereas both of its strengths are higher than those of a conventional grade Ti–6Al–4V alloy at high strain rate only. In addition to compression tests we also conducted tensile loading tests on the laser-deposited alloy at both low and high strain rates (0.1/s and 1000/s). There is significant tension/compression asymmetry in the mechanical response under high-strain-rate loading. It was found that the quasi-static tensile fracturing exhibits typical composite fracture characteristic with quasi-cleavages and dimples, while the high-strain-rate fracturing is characterized by ductile fracture behavior.