Study On Preparation And Production Technology Of Oxide Ceramic For Nickel Alloy Mold Precision Casting

Nickel based superalloy has high strength,good oxidation resistance and cavitation resistance at high temperature in the range of 650~1000?.It is widely used in high temperature corrosion environment such as engine turbine blade,valve seat ring,ultrahigh temperature oxidation resistant corrosion furnace roller,radiant tube and so on.However,the applications of Ni based alloys had limited by some defects,such as difficulty in marking complex shape castings,long cycle,slow production and surface pores formed by the reaction between shell and liquid niclkel.Therefore,the preparation of high quality nickel-based alloy has become a widespread concern.This article made suitable for nickel alloy investment casting ceramic shell in several aspects,such as shell makong material selection,wax processing,the choice of binder,sand preparation,coating,spraying,drying,and roasting and so on.This paper also discusses the requirements and conditions of the shell making.Then,the zirconia composite shell is prepared with silica sol on the back layer,yttrium sol is used in the surface layer and the other zirconium sol is used in the rest.WM114 wax is selected for the wax.Sand is selected with mixed sand,which ensures the shell has high quality cavity surface,and has enough high temperature strength and good thermal expansion and thermal stability.It is proved by experiments that the composite shell investment casting process has lower manufacturing cost,shorter shell making period and higher quality standard than those produced by common process casting,and can be widely applied to mass production of Ni based superalloy.The shell strength increases with the increase of powder liquid ratio,fine powder content and forging temperture.When the temperatureis between 380 to 1200?,the thermal expansion coefficient of the back layer and the surface layer of shell isrelatively stable.When the temperature exceeds 1200 ?,the thermal expansion coefficient of the back layer starts to increase,while that of the surface layer decreases.If the temperature is too high,cracks or layers will form on the shell.Shell roasting process is heating 200? insulation 1 hour,heating to 400? insulation 1 hour,and then to 1150? 2 hour.The casting made by composite shell technology have no crack and surface finish is qualified,which meets the application requirements.