Preparation And Properties Of Shell For Ni Based Superalloy Casting

Ceramic shell properties have great influence on the quality of superalloy castings by investment castment processing.The relationship between raw material and shell performance has been studied in present paper.And ceramic raw materials mainly include two kinds of the refractory material,kaolinite and corundum,as well as two kinds of silica sol binder.Shell Strength,deflection,permeability and interface stability have been researched.According to phase evolution and formation mechanism of ceramic material at different sintering temperature,the relationship of shell properties and phase constitute.There are two kinds of binderd,such as FSIII silica sol(F silica sol)and GS30 silica sol(G silica sol),as well as five kinds of refractory including EC95,zirconium silicate,,coal series(1#)and non-coal series(2#)Kaolin,have been used as main materials of shell sample.The phase structure of two kinds of Kaolin powders were analyzed by the means of XRD and DSC.The strengths and deflection of the shell have been studied by three-point bending test and self-loading deformation at high temperature,respectively.Shell permeability has been measured at different temperatures using high temperature permeability equipment.Interface reaction between different kinds of refractory powder or the shell surface and superalloy melt have been studied in this paper.Cristobalite,mullite,quartz and quartz glass phase were observed in Kaolin,but two kinds of Kaolin consist of different phase contents.Compared with the room temperature strength,high temperature strength of two kinds of kaolin shell were significantly improved.The crystallization of the quartz glass transition,cristobalite transformation and mullitization has been formed at high temperature.However,different shell system has special phase transformation mechanism.Effects of silica sol compositon on shell strength were ignorable.Compared with cristobalite,quartz glass has a promoting effect on the formation of a mullite,mullitization can improve the high temperature strength of shell and decrease the retained strength of shell.High temperature deflection of Kaolin shell increased dramatically above the temperature of 1500?,while EC95 shell increased gradually at the range of 1000-1600?.After sintering,Kaolin shell bends toward to back layer instead of toward to direction of gravity.Organic material increased deflection of kaolin shell,but it is not obvious to influence EC95 shell.Because of different thermal expansion rate between corundum and kaolin layer,creep deformation in the opposite direction of gravity occurred.EC95 shell deformation is caused by viscous flow of the quartz glass.At the temperature range of 1000-1400 ?,high temperature permeability rise steadily,but refractory has little influence on shell permeability.Over 1400?,the permeability of kaolin shell increased significantly.With the increase of test temperature,EC95 shell rate of permeability rise fast at first,and then rise slow.Amorphous silica can be transformed into cristobalite or react with EC95 powder to form mullite.Serious reaction between 417 G and yttrium oxide were observed Silicon carbide is not applicable to shell surface agent.Both EC95 and zirconium silicate have slight interface reaction with alloy.Mechanical scab between 417 G and EC95 layer were observed while chemical scab between 417 G and zirconium silicate occurred.