(西安理工大學 材料科學與工程學院，西安 710048)
摘 要: 采用熔融玻璃凈化與循環(huán)過熱相結合的方法研究過冷Ni-40%Pb(質量分數)過偏晶合金的組織演化規(guī)律。結果發(fā)現：過偏晶合金在快速凝固階段本質上是以枝晶方式生長；當ΔT<50K時，合金組織為粗大枝晶＋枝晶間Pb相＋團塊狀Pb相；當100<ΔT<198K時，合金組織宏觀偏析嚴重；當ΔT＝292K時，合金組織呈粒狀晶，第二相均勻彌散分布。分析表明：凝固組織宏觀偏析與快速凝固階段固液相變速率和體系殘余液相分數有關；粒狀晶粒化機制屬于枝晶碎斷-再結晶機制。
關鍵字: 深過冷； NiPb過偏晶合金； 枝晶生長； 組織粒化
deep-undercooled Ni-40%Pb hypermonotectic alloys
（School of Materials Science and Engineering, Xi′an University of Technology,
Xi′an 710048, P.R.China）
Abstract:Structural evolution in undercooled Ni-40%Pb(mass fraction) hypermonotectic alloys was investigated systematically by employing the method of molten glass purification combined with superheating cycling. Within the achieved undercooling range of 0 to 292K, the structures were classified into three categories. When the undercooling was less than 50K, coarse dendrites and interdendritic lead lumps comprised the major characteristics of hypermonotectic alloys. With increasing the undercoolings into the range of 100K to 198K, the macrosegregation was serious. When the undercooling was up to 292K, the granular grains formed, and the refined lead particles distributed homogeneously in the whole sample. Analytical result shows that the degree of macrosegregation is related to the solid/liquid phase transition velocity and the residual liquid fraction during the rapid solidification stage. The granulation mechanism of undercooled granular grains is owing to the dendrite breaking-up and recrystallization.
Key words: deep undercooling； Ni-Pb hypermonotectic alloy； dendrite growth； structural granulation
