With the rapid development of additive manufacturing technology, Ti-6Al-4V alloy, as an excellent metallic material, has been widely used in aerospace, medical, and automotive fields. However, in traditional processing methods, there is often a trade-off between strength and ductility in this alloy. To overcome this challenge, researchers have started exploring the use of heat treatment to achieve optimal strength and ductility in Ti-6Al-4V alloy.
The SLM Ti-6Al-4V alloy exhibits poor ductility and uneven performance due to the presence of acicular α' martensite and columnar β grains. Post-heat treatment can improve its microstructure and performance.
The SLM Ti-6Al-4V alloy exhibits poor performance and unevenness due to the presence of columnar β grains and acicular α' martensite. By optimizing SLM process parameters or conducting solution annealing and aging treatment, the comprehensive mechanical properties of SLM Ti-6Al-4V can be improved and anisotropy can be reduced, but the plasticity of the samples is still lower than that of traditionally manufactured Ti-6Al-4V alloy.
SLM Ti alloys can obtain equiaxed microstructures, improve ductility, and reduce anisotropy by appropriate heat treatments. Rapid heat treatment or cyclic heat treatment can further optimize the grain structure and performance, making SLM Ti alloys comparable to traditional Ti alloys.
Currently, there are no reports on achieving a three-modal microstructure in SLM Ti-6Al-4V alloys. This study systematically investigates the effects of single-step and multi-step high and low-temperature heat treatments on microstructure evolution, mechanical properties, and anisotropy behavior, and explores the spheroidization mechanism of α laths and the role of high-temperature annealing in eliminating mechanical property anisotropy.
The main conclusions are as follows:
- The microstructure of the samples consists of columnar β grains and graded acicular α' martensite. Due to the uneven microstructure features, high-density dislocations, and nano twins, the AF samples exhibit high strength (1368-1418 MPa) but low ductility (3.3-7.4%) and significant mechanical anisotropy. The elongation in the horizontal direction is 124% higher than that in the vertical direction.
- Single heat treatment decomposes the α' martensite into equilibrium α+β phases, and the width of α laths slightly coarsens with increasing temperature. The elimination of high-density defects improves ductility (6.8-13.1%) at the expense of a decrease in strength by 100-200 MPa. In addition, the anisotropy of mechanical properties is significantly reduced.
- High-temperature annealing and low-temperature aging treatment (HLT) endow the SLM Ti-6Al-4V alloy with a three-modal microstructure and excellent mechanical properties, with a UTS of 1089-1092 MPa and an elongation of 15.8-18.5%, surpassing that of traditional Ti-6Al-4V alloy. HLT treatment also eliminates the anisotropy of mechanical properties.
- HLT treatment can help fully activate dislocations and provide additional driving force for spheroidization behavior. The spheroidization mechanism of αgrains can be attributed to boundary splitting and circularization.
In conclusion, optimal strength and ductility can be achieved in Ti-6Al-4V additive manufacturing through heat treatment. High-temperature annealing and low-temperature aging treatment (HLT) can regulate the microstructure of the material, activate dislocations, and promote spheroidization behavior, thereby enhancing the mechanical properties. With HLT treatment, Ti-6Al-4V alloy not only exhibits excellent mechanical performance but also eliminates anisotropy, providing more possibilities for its widespread application in engineering fields.
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