摘要
Ni基偏晶合金是一种优良的自润滑耐磨材料,其组织形成规律对力学性能的影响十分关键。在自由落体条件下,对不同成分二元Ni-Pb偏晶型合金的快速凝固进行了实验研究。随着液滴直径的减小,Ni-20%Pb亚偏晶合金中α-Ni枝晶生长经历"粗大枝晶→等轴晶→蠕虫状枝晶"的转变。Ni-31.4%Pb偏晶合金的凝固组织以偏晶胞为主,偏晶胞的体积分数随液滴直径的减小而增大。过偏晶合金的快速凝固过程中均发生液相分离。Ni-50%Pb过偏晶合金中L2(Pb)相平均尺寸和最大尺寸均随液滴直径的减小先增大后减小。当液滴直径小于400μm时,Ni-60%Pb过偏晶合金由壳核组织演变为L2(Pb)相分布在α-Ni相枝晶间的偏析组织。根据Borelius脱溶模型、Gibbs-Thomson关系和LSW(Lifshitz-Slyozov-Wagner)理论,分析了合金成分、液相分离时间和第二液相体积分数对凝固组织形成的作用机制。
Four different Ni-Pb binary monotectic alloys have been rapidly solidified during free fall in drop tube.With the decrease of droplet diameter,the primary α-Ni dendrite in Ni-20%Pb hypomonotectic droplets shows a morphology transition of ＂coarse dendrite→equiaxed dendrite→vermiculate dendrite＂.The solidification microstructure of Ni-31.4%Pb monotectic alloy is mainly composed of monotectic cells,the volume fraction of which increases with the decrease of droplet diameter.Liquid phase separation has happened during the rapid solidification of both Ni-50%Pb and Ni-60%Pb hypermonotectic alloys.The grain size of L2（Pb） phase in Ni-50%Pb alloy increases and then decreases when the droplet diameter decreases.The microstructures of Ni-60%Pb alloy droplets display a ＂core-shell→dendrite＂ transformation as the droplet diameter becomes smaller than 400 μm.Theoretical analyses of Borelius model,Gibbs-Thomson equation and Lifshitz-Slyozov-Wagner（LSW） theory reveal that alloy composition,phase separation time and volume fraction of minor phase play important roles in the formation of core-shell microstructure.
出处
《航空学报》
EI
CAS
CSCD
北大核心
2011年第2期351-359,共9页
Acta Aeronautica et Astronautica Sinica
基金
国家自然科学基金(50971105)
陕西省自然科学基础研究计划(2009JQ6002)
西北工业大学基础研究基金(JC201050)~~
关键词
偏晶合金
液相分离
偏晶胞
枝晶生长
自由落体
monotectic alloy
phase separation
monotectic cell
dendritic growth
free fall
