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Metal Injection Moulding of Titanium Medical Components

The metal injection moulding technique is already established for serial production of complex parts, mostly from various stainless steels. However, for other materials, especially for titanium parts there is still the need for superior purity and enhanced surface quality. Facing the challenge of obtaining suitable medical titanium MIM parts, advances have been made at Fraunhofer IFAM over the last few years.One strategy to overcome the high risk of carbon up-take was to adjust the sintering program. Very low Argon flow rates, 50 mbar pressure and two hours dwell time at 1350°C were found to be optimal parameters. A cleaning cycle prior to the actual sintering at 1450°C under hydrogen was also found to enhance the results.Another strategy involved the choice of binder components. Stearic acid, which is often used to improve wettability of binder to powder particle, and high polymer content affect the oxygen content of the titanium parts. Low amounts of both are beneficial for high purity parts.Other investigations were performed concerning the surface quality. It was found that the surface roughness of the mould has an effect on the surface roughness of the sintered parts. Although sintered titanium surfaces as such exhibit quite rough surfaces of about 2-3 µm (Ra value) the influence of the surface finish of the mould was detectable. Using very fine powders of only 15 µm mean particle size and a polished mould a very low surface roughness of less than 1.2 µm on the sintered part was obtainable.