Fabrication of high strength pure titanium by mechanical milling and spark plasma sintering and its properties

Pure titanium powder was mechanically milled (MMed) using a vibrational ball mill in the presence of stearic acid, which was added as a process control agent (PCA). The MMed powders were subsequently consolidated into bulk materials by spark plasma sintering (SPS) to enhance the mechanical properties of the titanium. Changes in hardness, constituent phases and powder particle size resulting from the milling process were investigated by microhardness measurements, X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The hardness and microstructure of the SPSed materials was also studied by hardness measurements and optical microscopy, respectively. The Vickers microhardness of the titanium powders with 0.25 g of PCA was found to increase sharply from 189 to 513 HV after 8h of mechanical milling (MM), and SEM observations revealed that the mean particle size changed from 24 to 10 μm. Following SPS for 0.5 h under an applied pressure of 49 MPa at a temperature of 1073 K, near-full density was achieved for the sintered material. Formation of TiC by solid-state reaction was observed for the SPS materials consolidated from 4 h and 8h of MMed powders. In addition, formation of TiN was observed for the SPS materials consolidated from 8 h of MM with 0.50 g of PCA. A maximum Vickers hardness of 1253 HV exhibited for the SPSed material fabricated from 8 h MMed powder with 0.50 g of PCA.