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在Al—Ti晶粒细化剂中存在硼时,使用效果很好,这一点为人们所知已几乎40年了。有三种主要理论解释过这种现象:(1)硼改变Al—Ti—B系中的重要相关系;(2)硼形成TiB_2,它几乎是不可溶解的,在晶粒细化方面起着有效的成核作用;(3)形成亚稳定相(Al,Ti)B_2,它或者直接起着晶粒细化剂的作用,或者像(1)那样以某种方式改变相关系。然而,对这些理论的严格考察发现,没有一种理论能圆满地解释试验结果。因此,为了进一步阐明硼的重要作用进行了试验研究。发现在一些合金中,(Al,Ti)B_2相是有效的成核剂,这与过去的研究是一致的。此外,本研究表明,硼通过改变TiAl_3晶核的表面结构,可以成倍地改进Al—Ti中间合金细化晶粒的效果。因此,晶粒细化的机理比一般已了解的要复杂得多。
The use of boron in Al-Ti grain refiners works well for almost 40 years. Three main theories explain this phenomenon: (1) boron changes the important relationship in the Al-Ti-B system; (2) boron forms TiB_2, which is almost insoluble and effective in grain refinement (3) a metastable phase (Al, Ti) B 2 is formed which either acts directly as a grain refiner or changes the phase relationship in some way as (1). However, a rigorous examination of these theories reveals that no theory can satisfactorily explain the results of the experiment. Therefore, in order to further clarify the important role of boron was studied. It was found that the (Al, Ti) B 2 phase is an effective nucleating agent in some alloys, which is consistent with the previous studies. In addition, the present study shows that by changing the surface structure of TiAl_3 nuclei, boron can improve the effect of grain refinement of Al-Ti master alloy several times. Therefore, the mechanism of grain refinement is much more complex than generally understood.