Mass Production of Low Cost Titanium Powder
As part of the UK Government's drive to lower weight in transportation applications and cut exhaust emmisions (see www.technologyprogramme.org.uk) an ultimate objective is to remove the cost and quality barriers inhibiting the wider use of titanium in powder metallurgy (PM) and Metal Injection Moulding (MIM) components and extending its use, not just in the traditional aerospace and medical sectors, but to mass production applications in automotive and general engineering.
The global market is responding by significantly increasing capacity in primary titanium extraction and simultaneously developing new methods to replace the outdated, expensive Kroll method, with lower cost processes e.g. MER-Dupont, Armstrong and Fray. This, coupled with the further lowering of cost to convert primary titanium to spherical powder by the new PSI process - including CP-Ti, TiAl6V4 and intermetallic TiAl - will enable the titanium PM sector to rapidly expand.
The potential for this sector has been identified for many years, research is complete, and prototypes have been successfully tested e.g. the engine thrust link for the new Boeing 787 ‘Dreamliner’ supplied by GKN Aerospace. All that is required to release many new engineering applications is for titanium powder costs to fall. Powder Metallurgy, as the most rapidly growing metal forming technology, is expected to feature heavily in the expanded usage.
Over twenty years, PSI has progressively developed gas atomisation as a means of producing fine, pure and spherical, metal powders. More recently it has concentrated on improving yields and lowering costs of the valuable fine fractions of atomised powders. To this end it has introduced “hot gas” atomisation to the market, constructed atomisers for continuous rather than batch production and fitted gas recycling, all with the objective of lowering unit production cost.
Titanium poses a special challenge in that during the melting and feeding stage, as part of the atomising process, the liquid metal must not contact ceramic refractory at any stage; otherwise it will be contaminated by oxygen and ceramic inclusions rendering it unusable for many advanced aerospace applications.
Ceramic free, “Cold Wall” melting and feeding techniques must be used throughout and this approach will be adopted in the programme enabling high quality, low cost aerospace grade powders to be made. To achieve low cost, production will be continuous and at a high throughput rate for similar reasons to those which led continuous casting to replace ingot casting in steel production. PSI’s developments in cold wall melting techniques now make this possible for titanium.
The technology will apply equally to more complex titanium alloys and the clean melting techniques will be of interest to users of superalloy powders, nickel-titanium shape memory alloys and indeed any metal powders that are required to be ceramic inclusion-free.
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