Ultralow Temperature Densification of a Titanium Alloy by Spark Plasma Sintering

Full densification of a Ti alloy (Ti6Al4V) is achieved at unprecedented low temperatures of 650 degrees 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 degrees 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 x 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 degrees C.