Höganäs explores lower cost route to PM titanium components
July 9, 2014
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.
Fig. 1 Press and sintered titanium gear wheel. As-sintered (left)
and green (right). (Photo courtesy Höganäs AB).
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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