Ultralow Temperature Densification of a Titanium Alloy by Spark Plasma Sintering

Abstract

Full densification of a Ti alloy (Ti6Al4V) is achieved at unprecedented low temperatures of 650 °C and 555 MPa by spark plasma sintering (SPS) without any sintering aid. The alloy demonstrates a globular equiaxed microstructure with comparable mechanical properties as that sintered at conventional high temperatures (950 °C, 60 MPa). In contrast with the diffusion‐driven sintering of the Ti alloy at conventional SPS conditions, the near‐full densification (99%) attained at low‐temperature/high‐pressure regimes is attributed to plastic deformation‐driven mass transport processes. Sintering pressures of 555 MPa result in a dislocation dense microstructure and the activation of compressive twins imparting lattice strains of up to 2.86 × 10−3, suggesting a 25% increase in lattice distortions as compared with those sintered at moderate pressures of 60 MPa. Depth‐sensing nanoscale indentation reveals the globular microstructure of the high‐pressure‐sintered alloy to retain its elastic modulus and hardness of 138 and 4.8 GPa, respectively, with <2% deviation from those sintered at conventional SPS temperatures. This energy‐efficient technique proposes an alternative to thermally exhaustive routines and presents an advantage for engineering titanium‐matrix composites with nanofillers and controlled reaction products by reducing processing temperatures by up to 300 °C.