Synthesis of Ultrafine Crystal/Nanocrystalline TiAl-based Alloy by in Situ Sintering

The preparation of TiAl-based alloys with ultrafine crystal/nanocrystalline by in situ sintering was investigated. TiH2, Al, Si and Nb powders were firstly refined to the nanoscale level by ball milling; then, the milled powders were pressed into green compacts, which were sintered into bulks by spark plasma sintering (SPS). The functional characteristics of milled powders and sintered bulk were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). High temperature oxidation resistance was examined by differential scanning calorimeter (DSC). The results reveal that amorphous products, Ti3Al nanocrystalline and decomposition products of TiH2 are formed during milling. When milled powders are sintered at high temperature, these fine powders rapidly transform into TiAl and Ti3Al phase. The grain sizes of TiAl and Ti3Al are 500 nm∼1 μm and a few nanometers, respectively. This sintered bulk ultrafine microstructure is quite stable below 1000 °C, and has excellent oxidation resistance.