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Influence of Powder Particle Size Distribution on the Properties of Press-and-Sintered Titanium and Ti-6Al-4V Preforms

The potential to control the final properties, as measured by density, strength and microstructure, of press-and-sintered titanium and master alloy Ti-6Al-4V is investigated by designing and evaluating bimodal particle size distributions of the relevant powders. Ratios of 1/3, 2/3 and 1/1 by volume of coarse to fine powders, as determined by particle size peaks, were blended from -200 and -100 mesh commercially pure titanium powders and -200 mesh 60Al-40V master alloy powder, in the case of Ti-6Al-4V. The powder blends were uniaxially compacted at 350, 400 and 450 MPa, and the green specimens were sintered under high vacuum for two hours at 1300°C. The results support theoretical prediction of green and sintered density based on the ratio of the volume percentage of coarse to fine powder; green density increases as the ratio of coarse powder increases for both the pure and alloy titanium, while the sinter density similarly decreases for the pure titanium. Microstructural observations of the sintered specimens show that the pore size decreases, and the pore shape becomes more rounded, as the ratio of fine powder increases. In order to extend the study to find the optimal packing ratio, and potentially the optimal blend for densification, further refinement of the initial powder particle size distributions is needed.