Sintering Of Ti-47Al-xAl₂O₃-yCr Nano-powder By Mechanical Activating-Spark Plasma Sintering

Due to the high Specific strength and good performance at elevated temperature, Ti-Al intermetallic compound is regarded as the most hopeful high-temperature structural materials. But the inherent poor ductility at room temperature has seriously limited its applications. As a newly developed process, compared to traditional ones, SPS has the superiority of short sintering time, low sintering temperature and the good ability that can sinter the powders into very compact mass. In this paper, for the ultimate purpose of gaining the fine-grain structure to improve the ductility at room temperature, the mechanically activated nano Ti/Al powder was used to sinter on SPS while the sintering mechanism was put forward. Powders such as Al₂O₃ and Cr of different content were put into original powder for mechanical milling and sintering as a attempt to alloy.Experiments shown that among the powders which were mechanically milled for 50 hours, the grain size of Ti and Al is on the average 23nm and 49nm.They are mixed equably and don't form any alloy. According to the result of milling, with the increase of the Al₂O₃ added into the original powder, the grain size of Ti and Al after milling is gradually decreased; the grain size of Ti doesn't change markedly and the grain size of Al reaches its minimum when the content of Cr added into the original powder is wt%5.0n SPS, the compact Ti-Al intermetallic compound is gained when the process is adopted that the powder is heated to 900 ℃ in 5 minutes and held for 5 minutes, during which the pressure of 40MPa is employed. The sintering of Ti/Al -Al₂O₃ powder in nm scale on SPS is composed of those moments: originally pressing period, exhausting and intenerated period, Al's consumption period,Al₂Ti's creation period, the main alloying and consolidation period and homogenization period. The consolidation happens mainly when the temperature is from 700℃ to 850℃;the reaction of forming alloy happens during the temperature is from 500℃ to 850℃.The increase of Al₂O₃ will increase the temperature of sintering and decrease the density of the mass; that of Cr will decrease the temperature of sintering and reaction heavily.In this paper, SPS and mechanical milling are combined to form Ti-Al intermetallic compound, and some parameters are gained, which is useful for subsequent work.