First-principles Study On The Effect Of Point Defects On The Electrical And Mechanical Properties Of Cr20Ni80 Alloy

Cr20Ni80 alloy is an electric heating alloy that is austenite at room temperature and high temperature.Because of its high resistivity and stability,e xcellent mechanical properties and long service life,it is widely used as a heating element in machinery,metallurgy,and military industries.Point defects have a great influence on the electrical and mechanical properties of the alloy.Its will destroy the periodicity of the crystal lattice,causing strong scattering of electrons,thus affecting the resistivity of the alloy,and point defects will change t he inter-atomic properties of the alloy.Bonding strength causes changes in the mechanical properties of the alloy.However,point defects are only at a atomic scale,and it is difficult to observe through experiments directly.The first principles can intuitively simulate and analyze defects in crystals through modeling,and the results are credible.Ba sed on this,this article uses combination first-principles calculations with experiments to study the effect of point defects on the electrical and mechani cal properties of Cr20Ni80 alloy.In the first principles,density functional theory is used to specifically analyze the elastic properties and electronic structure of each system with or without defects,and reveal the effect mechanism of point defects on the electrical and mechanical properties of Cr20Ni80 alloy from the micro level;In the experiment,the influence of point defects on the phase,microstructure,mechanical properties and resistivity of Cr20Ni80 alloy was analyzed by XRD,metallographic st ructure,room temperature tensile and resistance measurement methods.The main conclusions are as follows:The Cr20Ni80 alloy model(Ni₂₆Cr₆)was constructed successfully.When Al and Fe are doped in the system,both Al and Fe occupy in Ni sites,which can improve the stability of the system.Elastic calculation results show that doping makes the bulk modulus,Young's modulus and shear modulus of each system decrease,while the value of Poisson's ratio increases,indicating that the stiffness between atoms decreases and the hardness decreases but plasticity is enhanced after doping.The energy band calculation results show that doping will increase the resistance of the alloy.The conclusion of the experiment is consistent with the trend of the first-principles calculation.The addition of Al and Fe will increase the resistivity of the alloy,reduce the strength and hardness,and increase the plasticity.The narrowing of the energy range of the conduction band of the alloy and the enhancement of electronic localization are the fundamental reason for the increase in the resistivity of the alloy due to doping.The electron cloud between atoms in the system is redistributed,and the bonding strength between atoms also changes accordingly.This is the root cause of the changes in the mechanical properties of alloys caused by doping.Therefore,the first-principles calculation results essentially reveal the mechanism of the effect of replacement defects on the mechanical and electrical properties of Cr20Ni80 alloy.The vacancies cause lattice distortion of the alloy and lower stability.The energy band calculation results show that the presence of vacancies increases the resistivity of the alloy,but the resistivity of the 6.25%Cr vacancy concentration is slightly l ower than that of the 3.125%Cr vacancy,while the Ni vacancy is the opposite.The elastic calculation results show that the existence of vacancies reduces the stiffness and hardness of the system,and increases the plasticity.Only when the concentration of Ni vacancies increases,the plasticity decreases slightly.The experimental results show that as the vacancy concentration increases,the resistivity increases,which is consistent with the first-principle calculation of the influence of the Ni vacancy concentration on the resistance.This is because the increase in the vacancy concentration reduces the value of the highest energy point of the conduction band of the alloy.The increase in the localization of the electronics is caused by the increase in the effective mass of the electronics.The tensile results at room temperature show that with the increase of the vacancy concentration,the strength and hardness of the alloy decrease,while the plasticity increases,which is consistent with the trend of t he influence of the Cr vacancy concentration on the mechanical properties of the alloy in the first-principles calculation,and the bonding ability between atoms The weakening and increasing repulsive force are the essential reasons for the changes in the mechanical properties of the alloy.When the system has anti-site defects,the bulk modulus,shear modulus and Young's modulus all decrease different degrees,and the plasticity weakens when Ni _Cr.The analysis of the energy band structure also draws the conclusion that the inversion defect makes the alloy resistance increase.Doping,vacancy and anti-site defects can all cause the alloy resistance to increase,the strength is slightly reduced,and the plasticity is obviously increased.