PREP　TiAl基合金粉末冷凝组织特性

Features of the Solidified Microstructure of PREP TiAl Base Alloy Powders

在Ｈｅ气保护下采用ＰＲＥＰ工艺制取Ｔｉ－４８Ａｌ－１Ｖ（ａｔ％）合金粉末，观察粉末表面冷凝组织特性，估算冷却速率（Ｖｃ）和冷凝速率（Ｖｓ），并对其影响因素进行了分析讨论。结果表明，Ｖｃ值达到１０４～１０６Ｋ／ｓ，比在Ａｒ气气氛中的Ｖｃ值高。Ｖｓ值处在１．３１～１０．５７ｃｍ／ｓ范围。二次树枝晶臂间距（Ｓ）和初始β晶粒度（ｄ）随Ｖｃ变化规律分别服从幂函数Ｓ＝３４．２１ 和ｄ＝７２３ 。当粉末颗粒较大，Ｖｃ值较低时，结晶是完整树枝状，而当粉末颗粒较小，Ｖｃ值较高时，结晶呈胞状。这些结果表明，在Ｈｅ气保护下的ＰＲＥＰ快速冷凝效果比在Ａｒ气保护下的要好。

he powders of γ-TiAl base alloy(Ti-48Al-1V at%) were produced by PR EP in He atmosphere; the cooling rate(Vc) and the solidifying rate(Vs) have been estimated, the solidifying features and the resulted microstructure on the surface of powders were observed, and their influencing fsctors were analyzed. The investigated results showed that the Vc values reached the order of 104～106K/s, that is higher than the case in Ar atmosphere, and the Vs values were in the range of 1.31～10. 57cm/s. The regularity of Vc influencing the secondary dentrite arm space(S) and the initial grain size(d) obeyed the power function of s=34.21 , and d=723V , respectively. The complete dentrite appeared on the surface of the larger particulates for a lower Vc and the cellular solidifying features happened in the smaller particulates for a faster Vc. These results suggest that the RS effect of PREP in the Heatmosphere is more efficient than in the Ar atmosphere.