Structure of Nanocrystalline Ti-base Alloys Obtained by Mechanical Alloying and Ultra High Pressure Sintering

摘要

The Ti-base alloys with additions of Ta and Nb had been ball milled and subsequently sintered using ultra high pressure Bridgeman method. The milled powders with structure of α-Ti solid solution and average crystallite size of 10 nm and particle size of 5 μm were hot pressed under 4 GPa for 1 min at temperature 650 °C. This technique allowed preserving the structure of the examined alloys at a nanometric level. The grain size of alloys after UHP sintering changed from 25 up to 90 nm with an increase of content of the elements stabilizing the β phase in the alloy. The nucleation and growth of the β phase during sintering were major factors, which controlled the final structure of the sintered alloy. The Ti alloys containing additions of either Ta or Nb consisted mainly of the α-Ti structure with different fractions of β-Ti phase, whereas additions of both Ta and Nb generally increased the fraction of the β-Ti phase. Conventional TEM diffraction studies confirmed the presence of α-Ti and β-Ti phases in the investigated powders and HREM was applied to measure the grain size of both α and β phases.