Simulation And Experimental Study On Mechanism Of Competitive Growth Of Ni-Base Single Crystal Superalloy

Competitive growth of nickel-base single crystal superalloy during directional solidification was investigated by both a ProCAST simulation software based on a Cellular Automaton Finite Element(CAFE)model and experimental confirmation.Specifically,this paper aims at the mechanism of competitive growth of bi-crystals with orientation relationships both of convergence,divergence and non-plarnar in three dimensions.The behavior of competitive grain growth in the three-dimensional space is controlled by the temperature field and the solute field.The competitive growth phenomena of bi-crystals in the converging,diverging,and non-plarnar case different orientation can be obtained by the comprehensive role of temperature field and solute fieldIn converging case,the result of the grain growth depends on the combination of temperature field and solute field.The height of unfavored dendrite tip lagging behind favored dendrite tip at the front of the solidification interface can also influence the relative strength of the interaction between the temperature field and the solute field.Under certain solidification conditions,the critical value hk corresponds to the unfavored dendritic grain orientation ?K.If ?B>?K,the interaction of the solute field play a leading role in competitive growth,and unfavorably oriented gains advantage over favorably oriented gain.If ?B>?K,the temperature field is the major factor and the favorably oriented grain dominates superiority.In diverging case,the favorably oriented grain dominates and the grain boundary moves to the unfavorably oriented grain straightly under the combined action of temperature field and solute field.The dependence of grain boundary inclination ?GB on ?B can be divided into three stages:the linear increase phase of fixed slope,the slowly increasing phase with decreasing gradient and a stable near flat stage.In non-plarnar case,the favorably oriented grain is dominant,and the way of grain boundary propulsion is contralled by temperature field and solute field.If the unfavored grain orientation ?B is small,the favored orientation dendrites preferentially pass through secondary dendrites into the gap on the side of the shell which is away from the unfavored dendrite orientation.Secondary dendrites at the voids can produce parallel dendrites Of the first dendrites.Afterwards,the grain boundary advances in the x and y directions,and the unfavored grain B is eliminated finally.If the dendritic orientation ?B of the unfavored grain B is sufficiently large,the secondary dendrites of the favored grain A can smoothly grow into the unfvored grains B,instead of growing into the hetero-gap first,to extrud the space of grain B.finally,grain B is eliminated,with the grain boundary moving along the y direction only.