摘要
Primary dendrite arm spacing（PDAS） of α phase in directionally solidified Pb-26%Bi（mass fraction） hypo-peritectic alloys was measured by considering the effect of melt convection in cylindrical samples with different diameters.The experimental results show the measured PDAS increases with increasing diameter of the sample.At the growth velocity of 5 μm/s,its value changes from 161.5 μm for the sample with 1.8 mm in diameter to 240.4 μm for the sample with 7 mm in diameter.The strong melt convection in large diameter samples causes a high bulk alloy composition and a high concentration gradient in peritectic β phase,resulting in a larger PDAS.Simultaneously,the high concentration gradient could effectively promote the peritectic transformation,enhancing the dissolution of the thin α dendrite.
测量不同直径管中Pb-26%Bi(质量分数)亚包晶合金定向凝固试样的初生α相的一次枝晶间距,考察熔体对流对初生α相一次枝晶间距的影响。结果表明:一次枝晶间距随着试样直径的增大而增大。在凝固速度5μm/s,直径1.8mm的试样中的初生α相的一次枝晶间距为161.5μm,而在直径为7mm的试样中则增大到240.4μm。大直径试样中的熔体强对流将促进有效溶质扩散,加快包晶反应和包晶转变导致细小的α枝晶溶解,从而使得初生α相的一次枝晶间距增大。
基金
Project(50395100)supported by the National Natural Science Foundation of China
Project(NCET-07-0692)supported by the New Century Talents Program of the Ministry of Education,China
Project(34-TP-2009)supported by Open Project of State Key Laboratory of Solidification Processing,China
