Microstructure, Mechanical Properties at Room Temperature and High Temperature of Near-α Titanium Alloys Fabricated by Spark Plasma Sintering

A near-α titanium alloy was fabricated using spark plasma sintering (SPS) to investigate the effects of sintering temperature on its relative density, microstructure, and mechanical properties. The relative density increased significantly with temperature, reaching 94.56%, 99.91%, and 99.99% at 850 °C, 900 °C, and 1000 °C, respectively. At 850 °C, the alloy contained numerous pores, leading to low density, while at 900 °C, full densification was achieved, resulting in a bimodal microstructure comprising 20% primary α phase (average size: 2.74 μm) and 80% transformed β phase (average lamellar width: 0.88 μm). Nanoscale equiaxed α phase (375 nm) and dispersed nanoscale β phase (80 nm) were observed within the lamellar structure. A distinct L-phase interfacial layer (50–100 nm) was identified at the α/β interfaces with a specific orientation relationship. At 1000 °C, the microstructure transformed into a fully lamellar structure with wider lamellae (1.99 μm), but mechanical properties declined due to coarsening. The alloy sintered at 900 °C exhibited the best properties, with a tensile strength of 989 ± 10 MPa at room temperature and 632 ± 10 MPa at 600 °C, along with elongations of 9.2 ± 0.5% and 13.0 ± 0.5%, respectively. These results highlight the importance of optimizing sintering temperature to balance densification and microstructural refinement for enhanced mechanical performance.