The First-Principles Research On The Binary Compounds In Fe-C-V-Cr-Ce Alloy

In the chemical heat treatment,Rare earth is widely used duing to the advantage that it can improve penetration rate and the quality of permeation layer.RE chrome vanadium alloying,which possess the merit of single vanadizing and chromizing while overcome their shortcomings,has achieved great success in improving the life of cold die mold,and its cladding phase structure is mainly composed of Fe-C-V-Cr-Ce based compounds.However,the study of RE chrome vanadium alloying mostly focused on technological aspects currently,duing to the restrict of test means,complex experiments and trace RE.And the theory law of cladding phase structure still lack depth understanding,which has limited its further development.Therefore,we use first-principles method and calculate the basic physical properties and structural stability of Fe-C-V-Cr-Ce based binary compounds,try to analyze the exist possibility of various compounds after RE chrome vanadium alloying,which will be the good theoretical guidance for the further exploration of RE chrome vanadium alloying and the whole field of RE chemical treatment.In this paper,the lattice constants,electronic structure?Different charge density,Density of states?,thermodynamic properties?Debye temperature,Enthalpy of formation,Cohesive energy?,mechanical properties?Young's modulus,Shear modulus,Bulk modulus,Poisson ratio,Theoretical hardness,Anisotropy?of compounds in C-Ce,Fe-Ce,C-Cr,C-V four systems were calculated and analyzed by using CASTEP module.Meanwhile,the structural stability of binary compounds in Fe-C-V-Cr-Ce system were comprehensive analyzed by comparing with experimental data,And the main findings are as follows:Among the three compounds of CCe,C₂ Ce,C₃Ce₂ in C-Ce system,the enthalpy of formation and Cohesive energy of C₃Ce₂ are the lowest,and Debye temperature is the highest,and the values are-0.859 ev/atom,-6.999 ev/atom and 376 K respectively.which means the optimal thermodynamic stability.The bonding electron hybridization of C₃Ce₂ is more obvious and the covalent is stronger in density of states,which can lead to a more stable structure than CCe,C₂ Ce.Meanwhile,the higher theoretical hardness?9.905Gpa?of C₃Ce₂ means a better mechanical stability.So,C₃Ce₂ is the compound that most likely to generate in C-Ce binary system.Among the three compounds of CeFe₂,CeFe₅,Ce₂Fe₁₇ in Fe-Ce system,the enthalpyof formation?-0.440 ev/atom?and Cohesive energy?-4.940 ev/atom?of Ce₂Fe₁₇ are the lowest,and the Debye temperature?403 K?is the greatest,which means a better thermodynamic stability.Three compounds are all mainly composed of ionic bond,metal bond and covalent bond,while the strength of covalent and ionic bonding in Ce₂Fe₁₇ is higher.The anisotropy coefficient of Ce₂Fe₁₇ is 0.005,which means a good isotropic.The Young's modulus,shear modulus,hardness theory of Ce₂Fe₁₇ are 266 Gpa,102 Gpa,8.984 Gpa respectively,which are all greater than CeFe₅,CeFe₂.Overall,Ce₂Fe₁₇ is most likely to generate in Fe-Ce system.Among the four compounds of CCr,C₂Cr₃,C₃Cr₇,C₆Cr₂3 in C-Cr system,the enthalpy of formation of CCr is non-negative,which is a thermodynamically unstable phase.Cohesive energy?-9.144 ev/atom?and the enthalpy of formation?-0.171 ev/atom?of C₂Cr₃ are the lowest,and the Debye temperature?807 K?is the greatest,which means a stronger thermodynamic stability.Meanwhile,the more obvious hybrid between Cr-3d and C-2p in density of states of C₂Cr₃ means a better structural stability.In addition,the bulk modulus?324 Gpa?,Young's modulus?439 Gpa?and theoretical hardness?16.368Gpa?of C₂Cr₃ are greater than C₆Cr₂3?C₃Cr₇,So the mechanical properties of C₂Cr₃ are better.Therefore,C₂Cr₃ is most likely to generate in C-Cr system.Among the six compounds of CV,aCV₂,bCV₂,C₃V₄,C5V₆,C₇V₈ in C-V system,the highest enthalpy of formation?-0.617 ev/atom?and Cohesive energy?-9.187 ev/atom?of C5V₆ means the best compound-forming ability and structural stability,which followed by C₇V₈ and CV.The Debye temperature,bonding hybrid degree,theory hardness and bulk modulus of CV,C₇V₈,C5V₆ are very close,which are all stronger thanaCV₂,bCV₂and C₃V₄.So,CV,C₇V₈,C₅V₆ are all relatively easy to generate in C-V systems.Of which the Debye temperature were 921 K,923 K,858 K,the Theoretical hardness were 23.1 Gpa,24.4 Gpa,25.9 Gpa,and the Young's modulus were 485 Gpa,481 Gpa,424 Gpa.When the four systems were comprehensive analyzed,it's find that the thermodynamic stability and the mechanical stability of compounds in C-Cr,C-V system are general stronger than the compounds in C-Ce,Fe-Ce,which means that the compounds in C-Cr,C-V system are more easily generated.Combining with XRD standard patterns and experimental data,we can further inferred that C₂Cr₃,C₇V₈,C₅V₆ may also be present in RE chrome vanadium alloying cladding.