Nitrogen-induced powder formation of titanium aluminides during mechanical alloying

The authors formerly found that introduction of nitrogen gas into milling atmosphere improved drastically production yield of γ-based TiAl powder by mechanical alloying of a powder mix of Ti and Al. In this report, the role of nitrogen gas on the improvement in production yield of γ-based TiAl powder was investigated by three series of milling experiments. As a result, the authors found that: (1) nitrogen gas affects the formation of TiAl powder after milling in argon for a certain period; (2) TiAl powder formed by mechanical alloying has the crystal structure of Al supersaturated α-Ti phase; (3) the content of nitrogen gas in the milling atmosphere has a great influence on the yield; (4) concerning the mechanism, it is presumed that a layer of Al supersaturated α-phase was formed during milling in argon, and transformed into a solid-solution with nitrogen during milling under the existence of nitrogen gas, and thereby became brittle and was broken into the fine powder.