(中國(guó)科學(xué)院 金屬研究所, 沈陽(yáng) 110016)
摘 要: 研究了不同硼含量對(duì)Ti46Al8Nb合金晶粒尺寸的影響，發(fā)現(xiàn)硼化物以兩種方式從液相中析出： 當(dāng)硼含量較低、 冷卻速度較快時(shí)， 硼化物主要存在于枝晶間， 說(shuō)明凝固過(guò)程中硼被排出到液相， 在β枝晶間最后與枝晶耦合生長(zhǎng)形成硼化物； 當(dāng)硼含量較高、 冷卻速度較慢時(shí)，硼化物存在于枝晶干。 硼含量對(duì)枝晶形態(tài)的影響表明， 不同硼含量時(shí)盡管晶粒尺寸有很大差別， 但是合金的枝晶形態(tài)和枝晶間距并沒有明顯的變化， 并且在晶粒得到部分細(xì)化的Ti46Al8Nb0.4B合金中發(fā)現(xiàn)，未被細(xì)化的粗大晶粒與周圍的細(xì)小晶粒的枝晶形態(tài)完全相同， 并可來(lái)自于同一個(gè)β晶粒。這些實(shí)驗(yàn)結(jié)果表明： 硼化物對(duì)Ti46Al8Nb基合金晶粒的細(xì)化作用主要不是通過(guò)改變L→β的凝固過(guò)程得到的， 而是通過(guò)影響凝固后的β→α固態(tài)相變來(lái)實(shí)現(xiàn)的。
關(guān)鍵字: γ-TiAl基合金； 硼化物； 晶粒細(xì)化； L→β相變； β→α固態(tài)相變
（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
