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对Ti-46Al-8Nb(摩尔分数,%)合金进行布里奇曼型定向凝固实验,考察生长速度和试样直径对合金显微组织、相变路径和硬度的影响。结果表明,随着生长速度的增加和试样直径的减小,凝固过程由完全β相凝固转变为具有包晶反应的凝固过程,其最终显微组织为α2/γ层片及有α2/γ层片和B2相组成的多相组织。以上结果是由扩散和对流的减弱造成的溶质富集而引起的。包晶反应的发生往往导致严重的溶质偏析,其中溶质Al和Nb的偏析使得层片组织较为粗大。因此,在较高生长速度下发生包晶反应时,合金硬度值急剧下降,硬度曲线随着生长速度的增加呈不连续变化。严重溶质偏析导致的粗大层片组织也使得该成分合金的硬度低于其他Ti Al基合金的硬度。
Bridgman-type directional solidification experiments on Ti-46Al-8Nb (mole fraction,%) alloy were performed to investigate the effect of growth rate and sample diameter on the microstructure, phase transition path and hardness of the alloy. The results show that the solidification process changes from complete β phase solidification to solidification with peritectic reaction as the growth rate increases and the diameter of the sample decreases. The final microstructure is α2 / γ and α2 / γ Multilayer structure composed of ply and B2 phase. The above result is due to the enrichment of solutes caused by the weakening of diffusion and convection. The occurrence of peritectic reaction often leads to serious solute segregation, in which segregation of solute Al and Nb makes the lamellar structure coarser. Therefore, when the peritectic reaction occurs at higher growth rate, the hardness value of alloy decreases sharply, and the hardness curve changes discontinuously with the increase of growth rate. The coarse ply tissue resulting from severe solute segregation also makes the alloy of this component less hard than other Ti Al-based alloys.