Study On Interface Reaction Between DZ22B Superalloy And Ceramic Materials Used For Investment Casting

High temperature alloy investment casting technology is mainly used in the preparation of key hot end parts of aeronautical and aerospace turbine engines,such as turbine blades,integral turbine disk,guide apparatus,cartridge receiver and combustion chamber,etc.However,in the actual production process,close contact between alloy melt and ceramic shell/core at high temperature and high vacuum for a long time,the active elements in the alloy are prone to complex interfacial reactions with the oxide components in the ceramic shell/core,causing the casting surface to form the burnt-on sand,the hard spot,the blowhole and so on the flaw,therefore,the casting surface quality is worsen,the dimensional precision and subsequent machining of the casting is influenced,at the same time,there will be inclusions inside the alloy,the mechanical properties of the casting is reduced,this affects the qualified rate of investment casting production seriously.In this context,developing the interface reaction experiment between superalloy and ceramic mould under different conditions by the numbers,accurately revealing the characteristics and regularity of interfacial reaction between superalloy and ceramic mould,it has important theoretical guidance function to restrain or eliminate the interface reaction in investment casting production of superalloy investment.This topic aims at the oxide components commonly used in the production of investment casting,SiO₂,Al₂O₃,ZrO₂ crucible and corundum ceramic shell are selected,the combination way of vacuum induction smelting and inert gas protection is used,the interfacial reaction experiments of DZ22B superalloy melt and oxide ceramic materials under different melting temperature and holding time are carried out systematically.High resolution scanning electron microscope?HRSEM?,energy spectrum analyzer?EDS?and X-ray diffractometer?XRD?are used in this paper,the changing behavior of interface reaction morphology,composition and phase structure are studied contrastively,on this basis,quantitative thermodynamic calculation is combined,the formation law of interfacial reaction under different conditions is summarized,the effect of interfacial reaction on the burnt-on sand on the investment castings surface is reasonably revealed.The specific findings are as follows:?1?The interfacial reaction between DZ22B superalloy and Si O₂ ceramic crucible and the surface bonded sand depend on the actual melting temperature and holding time.When the holding time is 15 minutes,interfacial reaction occurs on casting surface at melting temperature of 1400?,the morphology of the reaction layer is discontinuous distribution.When the melting temperature is raised to 1500?,the interfacial reaction layer transition to continuous distribution state.When melting temperature reaches 1600?,a further increase in the thickness of the reactive layer.Melting temperature 1600?,with the prolongation of heat preservation time?15 min,30 min,60 min?,the thickness of interfacial reaction layer is increasing?2.3?m,3.4?m,4.3?m?.The result of composition analysis shows that the interface reaction layer is mainly HfO₂ phase,this is caused by the obvious redox reaction between the active element Hf in the superalloy and SiO₂ in the ceramic crucible.As the degree of interfacial reaction increases with the heat preservation time increasing,the phenomenon of sand sticking on the castings surface tends to be serious,the bonded sand is mainly composed of interfacial reaction product HfO₂ and crucible material SiO₂.?2?When the heat preservation time is 15 minutes,the interfacial reaction between DZ22B superalloy and Al₂O₃ ceramic crucible occures mainly at 1600?,the product phase is HfO₂,this is caused by the redox reaction of the active element Hf in the superalloy and the Al₂O₃ in the ceramic crucible.With the holding time increasing?15 min,45 min?,the interfacial reaction products are distributed discontinuous,and the average size of HfO₂ phase increases from 1.3?m to 2.6?m.Under the same holding time of 15 minutes,when the melting temperature is 1400?,no burnt-on sand on the casting surface.When the melting temperature is raised to 1500?,a small amount of sand clay made of crucible material Al₂O₃ appears on the casting surface.When melting temperature rises to 1600?,surface bonded sand is composed of interfacial reaction productand crucible material Al₂O₃.With the holding time increasing to 45 minutes,the phenomenon of sand sticking on the casting surface is more serious,in which the area occupied by the interface reaction product HfO₂ and the crucible material is obviously enlarged.?3?Under the conditions of melting temperature 1600?and heat preservation time 45 minutes,a weak interfacial reaction occures between DZ22B superalloy and ZrO₂ ceramic crucible,the reaction layer HfO₂ is formed by the substitution reaction between the active element Hf and the ZrO₂ in the crucible,the average size of the discrete interfacial reaction layer is only 1.8?m.?4?Because the molded corundum shell is mainly composed of Al₂O₃ powder and silica sol binder containing SiO₂ component,when the contact time is 15 minutes,the interfacial reaction between DZ22B alloy and Al₂O₃ ceramic shell increases with the increase of melting temperature,there is no interfacial reaction at 1400?,weak interfacial reaction occurs at 1500?,interface reaction intensifies at 1600?.Due to pore capillary tension in the surface layer of mold shell,the gravity action of metal liquid and the flow erosion effect on the mold shell during the melting process,leading to the formation of a physical permeable layer in the shell surface.With stress concentration causing by high temperature gradient on the surface of mold shell,jointly promoting the occurrence of burnt-on sand phenomenon.Under the conditions of melting temperature 1500?and heat preservation time 30 minutes,the alloy surface appeares 10?m surface layer shedding.When the melting temperature is1600?,because the degree of interfacial reaction is stronger,physical invasion takes longer,the temperature gradient on the surface of the shell is higher,so the phenomenon of burnt-on sand is the most serious at this temperature,finally,burnt-on sand of surface layer is formed with its size up to 1 mm.?5?The interfacial reaction of SiO₂ crucible,Al₂O₃ crucible,ZrO₂ crucible and Al₂O₃ ceramic shell is compared and analyzed,and quantitative thermodynamic calculation is combined,the thermochemical stability order of the four ceramic materials is:SiO₂ ceramic crucible<Al₂O₃ base ceramic shell<Al₂O₃ ceramic crucible<ZrO₂ ceramic crucible.