Simulation Study On The Effect Of Alloy Elements On The Interface State Of Austenite/Precipitated Phase

A large amount of alloyed elements are often added to alumina film austenitic heat resistant steel to obtain single phase austenitic structure.The addition of alloying elements not only plays a solid solution strengthening effect on heat-resistant steel,but also often interacts with the matrix to form precipitated phases,such as carbide,intermetallic compounds,etc.,which mainly plays a role of second phase strengthening and grain boundary strengthening.The influence of alloying elements on the properties of heat-resistant steel is not only related to the precipitated phase itself,but also closely related to the interface properties between the precipitated phase and matrix.It is important to understand the interface properties of heat resistant steel to improve its properties.However,it is difficult for current experimental methods to systematically study the interface binding state and its mechanism,especially the information at the microscopic level between the precipitated phase and the matrix.Based on this,this study takes austenitic heat-resistant steel precipitated phase Ni₃Al and NbC as the research object,and adopts simulation calculation to examine the interface properties between the precipitated and the matrix of heat-resistant steel.The first-principles method of density functional theory is used to study the influence of alloying elements on the interface structure and electronic properties ofγ-Fe/Ni₃Al andγ-Fe/NbC By analyzing the element segregation and clarifying the interfacial binding mechanism,I hope to reveal the essence of the microstructure of the interfacial structure on the atomic scale,and provide theoretical guidance for the composition optimization design of alumina film austenitic heat-resistant steel.（1）Takingγ-Fe（111）,Ni₃Al（111）and NbC（111）crystal planes as the research object,according to the surface energy calculation results,the 5-layerγ-Fe（111）surface model,5-layer Ni₃Al（111）surface model and 11-layer NbC（111）surface model are established.Considering the influence of different surface model terminals on the interface stability,theγ-Fe（111）surface models of 3 different terminals,the Ni₃Al（111）surface models of 12 different terminals and the NbC（111）surface models of 6 different terminals were established.A total of 36 differentγ-Fe/Ni₃Al interface models and 18 differentγ-Fe/NbC interface models were combined.Twelveγ-Fe/Ni₃Al interface models and sixγ-Fe/NbC interface models with independent structures were screened out,and their separation work and interfacial energy were calculated.For theγ-Fe/Ni₃Al interface,it is found that the separation work value is between 4.02-4.05J/m²,and the interfacial energy value is between 0.46-0.52J/m².The energy difference is very small,indicating that different terminals have little influence on the stability of theγ-Fe/Ni₃Al interface,and interface 2 is the most stable interface structure.Therefore,it is selected for follow-up research.The sixγ-Fe/NbC interfaces can be subdivided into three different C terminal interfaces and three different Nbterminal interfaces.The separation power range of the first three interfaces is 4.635-4.638 J/m²,and the interface energy range is 0.039-0.042 J/m².The separation power of the last three interfaces ranges from 4.641-4.646 J/m²,and the interfacial energy ranges from 0.032 to 0.034 J/m².It can be seen that the stability of Nbterminal interface model is stronger than that of C terminal interface model,among which interface 2 is the most stable,so it is selected for subsequent research.（2）The segregation position and tendency of alloying elements（Cr,Mo,Mn,Ti,Nb）in the Fe matrix at theγ-Fe/Ni₃Al interface have been studied.The results of segregation energy calculation show that Cr,Mo,Mn,Ti and Nball tend to segregate to position 1.Cr,Mo,Ti and Nbare easily segregated,while Mn is difficult to segregate.The segregation position and tendency of alloying elements（Cr,Mo,Mn,Ti,Nb,Al,Y,Zr）in the Fe matrix at theγ-Fe/NbC interface are also studied.It was found that Cr,Mo,Mn,Ti,Nb,Y and Zr were not easily segregated except Al.When the concentration of alloying elements was high,position 2 was the most prone to segregation.（3）The effects of segregation of different alloying elements on the stability ofγ-Fe/Ni3Al interface andγ-Fe/NbC interface were studied by calculating the separation work,interfacial energy and interfacial electronic structure.For the interface of the former,the order of the interfacial stability after segregation is Ti>Nb>Mo>Cr>Mn,where Cr,Mo,Ti and Nbincrease the electron cloud enrichment at the interface,improve the binding strength at the interface and enhance the interfacial stability,while Mn reduces the interfacial stability after segregation.Forγ-Fe/NbC interface,the segregation of alloying elements will reduce the interfacial stability,the order of strength is Y<Zr<Nb<Ti<Al<Mo<Cr<Mn.Interface stability is the worst when Y segregate,because the radius of Y atom is larger than Fe atom,resulting in larger interfacial spacing after segregation,interaction force of atoms are weakened.