Influence Of Zr Content On The Solidification Behavior And Property Of IN939 Superalloy

With the continuous improvement of the thrust weight ratio and thermal efficiency of advanced aeroengines,higher requirements are put forward for the structure of key hot-end components and the bearing temperature of the materials.Taking the complex thin-walled castings of superalloys represented by guider and casing in aeroengines as examples,they are prone form misrun during the casting process and the bearing temperature of the active materials is insufficient,leading to the decreasing the yield and service properties of the casting.Thus,in order to solve the problems of poor fluidity and unsatisfactory performance of IN939 superalloy used as aeroengines casing castings,the influence of zirconium（Zr）element on the solidification behavior of superalloy and the potential advantages of improving grain boundary strength were studied.Five kinds of IN939 superalloys with different Zr contents were designed,the effect of Zr content on the fluidity,microstructure,tensile properties,corrosion properties and oxidation behavior of IN939 superalloys was systematically studied.The mechanism of Zr element in IN939 superalloy was discussed,and the optimal Zr content in IN939 superalloy with excellent comprehensive performance was obtained.Serval conclusions are drawn as follows:（1）With the increase of Zr content,the fluidity increases firstly and then decreases.When the Zr content is 0.12 wt.%,the fluidity is the best,which is 43%higher than that of the superalloy with 0.06 wt.%Zr.The improvement of fluidity is mainly due to the increase of specific heat and liquid fraction of IN939 superalloy,and the reduced surface tension,liquidus temperature,liquid viscosity and dendrite growth rate.（2）The increase of Zr content reduces the incipient melting temperature of the superalloy from 1129.1℃to 1195.5℃.Zr aggravates the segregation of Ta,W and other elements,but has little effect on the segregation of Al,Cr.Proper amount of Zr can increase the volume fraction of??phase and carbide in the superalloy,and change the carbide from bulk and cursive shape to granular and long strip shape.With the increase of Zr content,the hardness of the superalloy increases,and the tensile properties at room temperature increase firstly and then decrease.When the Zr content is 0.12 wt.%,the tensile properties are the best.（3）With the increase of Zr content,the corrosion resistance of IN939 superalloy increases firstly and then decreases.When the Zr content is 0.15 wt.%,the superalloy has the most positive open-circuit voltage,the smallest corrosion current,the largest solution resistance,and the lowest corrosion tendency,indicating the best corrosion resistance.（4）The oxide scale of IN939 superalloy with different Zr content after oxidation at 1000℃consists of dense Cr₂O₃ outer layer and dendritic Al₂O₃ inner layer.Ni O and spinel（Ni/Co）Cr₂O₄oxides are mixed in the Cr₂O₃ layer.The oxidation resistance of IN939 superalloy can be improved by appropriate Zr addition.When the Zr content is 0.12 wt.%,the oxidation resistance is the best.When the Zr content is 0.15 wt.%,the oxide scale of the superalloy appears spalling and flaking,which deteriorates the oxidation resistance of the superalloy.