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 292 K, the structures were classified into three categories. When the undercooling was less than 50 K, coarse dendrites and interdendritic lead lumps comprised the major characteristics of hypermonotectic alloys. With increasing the undercoolings into the range of 100 K to 198 K, the macrosegregation was serious. When the undercooling was up to 292 K, 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.
Solidification structures in deep-undercooled Ni-40%Pb hypermonotectic alloys
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 292?K, the structures were classified into three categories. When the undercooling was less than 50?K, coarse dendrites and interdendritic lead lumps comprised the major characteristics of hypermonotectic alloys. With increasing the undercoolings into the range of 100?K to 198?K, the macrosegregation was serious. When the undercooling was up to 292?K, 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. [