It is difficult to produce titanium alloy powders with low oxygen content because of the high reactivity of molten titanium against to atmospheric gas and refractory materials. A new gas atomization process coupled with a cold crucible levitation melting and bottom tapping electric nozzle using its features as titanium melting furnace, supplies low impurities, high temperature and enough volume of molten metal, has been constructed. Thermal phenomena at bottom nozzle region, erosion resistivity of the sleeve, of which is one of the nozzle-constructed parts, to the molten titanium and atomization gas stream of this process have been revealed. Followings were found from experimental and numerical investigations. 1) Additional heat supplied by sleeve made of electrically conductive material inserted in the water cooled nozzle avoid nozzle clogging even for small radius nozzle. 2) Tungsten showed lowest erosion rate among the candidate materials for sleeve. 3) Conically enclosed space by atomizing gas induces unfavorable gas flow and low pressure region. Developed atomization system, electric bottom tapping nozzle and pencil nozzle for atomization, that is designed based on above results showed following features. 1) Tapping and atomization were stable and were continuously done without changing or repairing nozzle part. 2) Atomization yield was increased since the reuse of bottom skull was enabling. 3) This process allows the production of fine (d50=85μm) Ti-6Al-4V alloy powders.
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Okumura et al. (2006) studied this question.
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