Effect Of Cu On Phases Stability Of Inconel 718 Alloy: First-principles And Experimental Syudy

Inconel 718 alloy is an age-enhanced Ni-Fe-Cr based superalloy with remarkable stability,corrosion resistance and creep strength at elevated temperature.It has been widely applied in aircraft engines,gas turbines and other fields.However,when the using temperature of Inconel 718 alloy exceeds 650?or it is used for a long time at high temperature,the???phase in the alloy will lose the consistent relationship with the?matrix phase,and it will transform into the stable?phase,which degrades the properties of the material.The doping of alloying elements has an important inf luence on the properties of high-temperature structural materials.Since the minerals of copper and nickel are associated,the raw material of Inconel 718 alloy will contain Cu element inevitably.In general,Cu has a harmful influence on the superalloy.Therefore,the content of Cu in the alloy needs to be controlled to obtain the suitable raw material.In this paper,the effect of Cu on the structural stability,elastic mechanical properties and electronic structure of?phase,??phase and?"phase is analyzed by first-principles calculation.It is revealed that the mechanism of the influence of Cu on stability of phases from microscopic electronic scale.The effect s of Cu on the microstructure and morphology of Inconel 718 alloy are analyzed by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and X-ray diffractometry?XRD?and the change in hardness is compared.The research results are as follows:The first-principles calculation shows that the doping of Cu reduces the structural stability of?-Ni system,and the stability decreases with the increase of doping concentration.The elastic properties of the system are analyzed,indicating that the hardness,ductility,deformation resistance and bonding energy between the atoms are reduced with the doping of Cu.When Ni atom and Al atom in the?-Ni system are replaced by Cu atom,the bond between Ni and Cu is formed by valence electron hybridization of Cu 3d and Ni 3d orbitals.The experimental results show that the content of Cu has a great influence on the as-cast microstructure of alloy.The addition of Cu promotes the precipitation of Laves phase.Fu rthermore,the hardness,yield strength and elastic modulus of the alloy are reduced with the addition of Cu.Experimental results are consistent with the results of first-principles calculation.The first-principles calculation shows that the doping of Cu reduces the structural stability of?'-Ni₃Al system and Cu has a tendency to preferentially displace Al atom.The elastic properties of?'-Ni₃Al system are analyzed,indicating that the elastic constants of each model are reduced.Furthermore,the hardness,volume deformation resistance and the bonding ability between atoms are weakened.The chemical bonds of Cu-Al atom and Cu-Ni are weakened after Cu-adopted?'-Ni₃Al system,which lead to reduction of enthalpy and cohesive energy,revealing the essential cause of the decline of?'-Ni₃Al phase stability.Experimental studies have shown that the addition of trace amounts of Cu has a great influence on morphology of?'and?"phases which are precipitation phases of Inconel 718 alloy.The results of the first-principles study reveal the essential reasons for the decrease of the stability of Cu-doped into the Ni₃Al system and the change of precipitation morphology of?'phase.The first-principles calculation shows that the doping of Cu reduces the structural stability of?"-Ni₃Nb and Cu has a tendency to preferentially displace Ni.The elastic properties of the system are analyzed,indicating that the hardness,volume deformation resistance of?"-Ni₃Nb system are reduced with Cu-adopted.And bonding ability between atoms are weakened.Furthermore,the effects of Cu on ductility of?"-Ni₃Nb system are different.Inter-atomic hybridization,electron density and strengthen of atom bonding are weakened after Cu-doped??-Ni₃Nb,which lead to reduction of enthalpy and cohesive energy,revealing the essential caus e of the decline of?"-Ni₃Nb phase stability.The experimental results are consistent with the theoretical calculation.Cu makes the precipitation morphology of???phase from disc to coating,this transformation increases the lattice distortion caused by the precipitation of???phase,and it reduces the hardness of Inconel 718 alloy.Experimental studies have shown that the addition of Cu leads to the existence of Laves phase in the structure of Inconel 718 alloy after standard heat treatment,which has an important influence on the precipitation of?'phase and?"phase.And the addition of Cu reduces the hardness of alloy.Considering the experimental results and the first-principles computational results,Cu reduces the stability of matrix phase and strengthening phases of Inconel 718 alloy.Through the above research,the role of Cu in the matrix phase and strengthening phases of Inconel 718 alloy is determined from the microscopic electron scale,which provides theoretical and experimental basis for the selection of Inconel 718 raw materials.It is recommended to control the content of Cu in the alloy below 0.1 wt%.