Sweden’s Höganäs AB, one of the world’s leading ferrous powder producers, has been exploring the production of titanium powder for press and sinter applications using a process which, the company states, could reduce the cost of Powder Metallurgy titanium components by up to 75% compared with the use of atomised Ti powders.
Robert Frykholm stated in his presentation “Ti Alloys in PM Applications” at the PM2014 World Congress, Orlando, USA, May 19-22, that Höganäs has been using a pilot powder production unit capable of producing 10 kg/day of hydrogenated Ti powder or hydrogenated pre-alloyed powder having particle size of 6 to 10 micron.
For alloying, a master alloy with composition of 60%Al/40% V and particle size of 6 µm was mixed with the fine TiH2 powder to achieve Ti-6Al-4V.
Because of the fine particle size, the powder was treated with a polymeric lubricant to improve flow properties for die compacting. The die pressed treated powder showed good surface quality, green density (87%) and green strength when warm compacted at 600 MPa. Sintering at 1300°C in H2 plus vacuum at 1300°C resulted in densities up to 99.5% TD and sufficient chemical purity.
In contrast to low levels of dimensional change experienced in ferrous PM parts, the sintered Ti parts saw linear shrinkage of 14% using the TiH2 as the base powder. Shrinkage was expected to be substantial during sintering because the molar volume of TiH2 is larger than that of Ti or Ti-6Al-4V. An example of a titanium gear wheel in the green and sintered states as shown in Fig. 1.
Frykholm stated that Höganäs plans to expand the TiH2 powder facility to around 60 kg/day and to carry out further development work on microstructures and mechanical properties.
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