金型成形-普通焼結法による高密度TiAl焼結材の製造

Abstract

In order to develop highly densified TiAl by die compaction-sintering method, the sintering behavior of Ti(or TiH2)+TiAl3 mixed powders, promising as a starting powder, was investigated.The mixed powders were consolidated by cold pressing and sintered in vacuum without extermal pressure. In the sintering behavior, the densification characteristics of mixed powders were examined as a function of particle size and composition, and the microstructure and oxygen content of the sintered TiAl were also examined.The results were as follows:(1) The densification behavior of the Ti+TiAl3 mixed powders was influenced by the particle size of constituent powders, especially the size of Ti powder. With refining Ti powder, a greater densification over 95% relative density took place.(2) The densification behavior of the mixed powders was also inflienced by their composition. Although Al-rich TiAl of 55 at%Al showed a small densification irrespective of a proper adjustment of particle size, TiAl containing 40∼50 at%Al showed excellent sinterability. This is mainly due to the α-Ti phase which appears during sintering.(3) The microstructure of sintered TiAl of 55 at%Al consisted of a single γ-phase, while those of 40∼50 at%Al were composed of equiaxis γ-phase and γ⁄α2-lamellar structure. In the mixed structures, the amount of the lamellar structure increased with a rise of sintering temperature and decreased with an increase of Al content.(4) The oxygen content of sintered TiAl was dependent on the oxygen content of starting powders, de-waxing conditions, the amount of interconnected pores and so forth. It was found that the oxygen content of the highly densified TiAl obtained by this die compaction-sintering method was 0.45∼0.55% and an appropriate handling of starting powders made it possible to reduce them less than 0.4%.