Impact of heat treatment on microstructure and mechanical properties of titanium matrix composites
Researchers from China’s Nantong Institute of Technology have published a study on impact of heat treatment on the characteristics of TiB + TiC/Ti-6Al-4V composites produced via Directed Energy Deposition (DED) Additive Manufacturing in the journal Metals.
Titanium matrix composites (TMCs) fabricated by DED have been shown to address the issue of coarse columnar grains typically observed in additively manufactured titanium alloys. In ‘Effect of Heat Treatment on Microstructure and Mechanical Properties of (TiB + TiC) /Ti-6Al-4V Composites Fabricated by Directed Energy Deposition’, systematic annealing heat treatments were applied to in situ (TiB + TiC)/Ti-6Al-4V composites to refine the microstructure and tailor mechanical properties.
The results indicate that the plate-like α phase in the as-deposited composites gradually transforms into an equiaxed morphology with increasing annealing temperature and holding time. Notably, when the annealing temperature exceeds 1000°C, significant coarsening of the TiC phase is observed, while the TiB phase remains morphologically stable. Annealing promotes decomposition of acicular martensite and stress relaxation, leading to a reduction in hardness compared to the as-deposited state – this is mitigated, however, by the fact that the reticulated distribution of the TiB and TiC reinforcement phases contribute to enhanced tensile performance.
The study found that the resultant as-deposited composite achieves a tensile strength of 1109 MPa in the XOY direction, representing a 21.6% improvement over the as-cast counterpart, while maintaining a ductility of 2.47%.
According to the researchers, these findings suggest that post-deposition annealing is an effective strategy to regulate microstructure and achieve a desirable balance between strength and ductility in titanium matrix composites produced via DED Additive Manufacturing.
The full paper is available here.
gjjlhzc.ntit.edu.cn
