定向凝固过共晶Nb-Si基合金的组织优化

采用液态金属冷却定向凝固炉制备Nb-16Si-24Ti-10Cr-2A1．2Hf合金，凝固速率分别为1．2、6、18、36、50mm／min，随后对定向凝固速率为50mm／min的合金进行（1400℃，10h），（1450℃，10h）和（1500℃，10h）的热处理。研究了定向凝固速率和热处理温度对合金微观组织的影响。结果表明：合金的定向凝固组织主要由沿着试棒轴向生长的初生Nb5Si3相和耦合生长的Nbss／Nb5Si3共晶胞组成，在共晶胞边缘，有少量的Cr2Nb存在。横截面上共晶胞边界明显，随着凝固速率的增加，定向凝固组织明显细化，Nbss／Nb；Si，共晶胞形貌也发生变化。合金经过热处理，Nbss连成基体，部分CrENb相熔解，微观成分偏析减小。经过（1450℃，10h1热处理，实现了对过共晶Nb—Si基合金的组织优化。

Microstructure optimization of directionally solidified hypereutectic Nb-Si alloy

Nb-16Si-24Ti-10Cr-2A1-2Hf alloy was directionally solidified with withdrawal rates of 1.2, 6, 18, 36 and 50 mrn/min and then heat treated at 1400, 1450 and 1500℃with withdrawal rate of 50 mm/min for 10 h. The effects of withdrawal rate and heat treatment temperature on the microstructure were studied. The microstructure of directionally solidified alloy was composed of the primary NbsSi3, Nbss/NbsSi3 eutectic cells and Cr2Nb, which distribute paralleled to the growth direction. The microstructure becomes more refined with the increasing withdrawal rate, accompany with the evolution of eutectic cells morphology. After heat treatment, Nbss phase connects and forms a continuous matrix, and the Cr2Nb phase becomes smaller and distributes more dispersedly. After heat treatment at 1450 ℃ for 10 h, the alloy achieves balance between the optimization of microstructure and alleviation of solute segregation.