(中国科学院 金属研究所, 沈阳 110016)
摘 要: 研究了不同硼含量对Ti46Al8Nb合金晶粒尺寸的影响，发现硼化物以两种方式从液相中析出： 当硼含量较低、 冷却速度较快时， 硼化物主要存在于枝晶间， 说明凝固过程中硼被排出到液相， 在β枝晶间最后与枝晶耦合生长形成硼化物； 当硼含量较高、 冷却速度较慢时，硼化物存在于枝晶干。 硼含量对枝晶形态的影响表明， 不同硼含量时尽管晶粒尺寸有很大差别， 但是合金的枝晶形态和枝晶间距并没有明显的变化， 并且在晶粒得到部分细化的Ti46Al8Nb0.4B合金中发现，未被细化的粗大晶粒与周围的细小晶粒的枝晶形态完全相同， 并可来自于同一个β晶粒。这些实验结果表明： 硼化物对Ti46Al8Nb基合金晶粒的细化作用主要不是通过改变L→β的凝固过程得到的， 而是通过影响凝固后的β→α固态相变来实现的。
关键字: γ-TiAl基合金； 硼化物； 晶粒细化； L→β相变； β→α固态相变
（Institute of Metal Research, Chinese Acadamy of Sciences, Shenyang 110016, China）
Abstract:Research on different boron contents on the grain refinement effect of Ti46Al8Nb alloy was carried out to study the role of boron addition. The experimental results show that there are two ways for the precipitation of boride. When boron content is low and the cooling rate is relatively high, boride exists mostly in inter-dendrite area, showing that boron is pushed forward at the solidification front, and precipitates at last coupling with the dendrite growth. When the boron content is high and the cooling rate is relatively low, boride can exist at the dendrite arm. The observation of the dendrite morphology with different boron addition show that the morphology and the arm spacing of the dendrite are not changed essentially, though the grain size difference can be observed obviously, indicating that boron addition does not influence the solidification process. In the observation of partially grain refined Ti46Al8Nb0.4B alloy, it is found that the unrefined big lamellar and the refined lamella are formed from one same β grain. Besides, the dendrite and the boride morphology in the big grain and small grains are same. All these results show that the boron addition does not influence the solidification process, but promote the β→α transformation, so still grain refined lamella can be gained at last.
Key words: γ-TiAl based alloy; boride; grain refinement; L→β transformation; β→α transformation
