Study On Mechanical Properties And Interface Mechanism Of TiAlCrN Hard Coating Based On First Principle

Nickel-based superalloy is a kind of widely used material with stable high-temperature oxidation resistance,but poor machinability.Therefore,selecting suitable hard coating can improve the machining efficiency and tool life of cutting nickel-based superalloy.Hard coating is widely used in the field of mechanical processing.The new Ti Al N coating is formed by adding Al element on basis of Ti N coating,and its hardness and high temperature oxidation resistance are better than Ti N coating.With the continuous improvement of machining requirements,the cutting performance of the original ternary metal nitride coating can't meet the machining accuracy required at present.It is found that the addition of the fourth element(Cr,Zr,V,Nb,Si,etc.)on basis of ternary coating can obtain better coating properties.Due to the different preparation methods of the coating and the inevitable errors in the preparation process,the coating prepared is not uniform,and the coating performance is greatly different.Therefore,based on the first principles,this paper explored the mechanical properties of TiAlCrN coating in uniform state,calculated the different contents of Al/Cr elements in the coating,obtained the best element ratio,and analyzed the bonding performance between TiAlCrN coating and WC matrix.Based on the first principles,the ideal model of Ti₃Al N and Ti_1.5Al X_1.5N(X=Cr,Zr,V,Nb,Si)under uniform state was constructed by Materials Studio software,and the appropriate element doping position was selected under the condition of guaranteeing the most stable unit cell.The appropriate truncation energy and brillouin k point are selected from the calculation results to ensure the calculation accuracy and save the calculation time.The elastic constants of the coating were calculated by using CASTEP module,and the properties of hardness,stiffness,plasticity and Poisson's ratio were analyzed.At the same time,the state density diagram of the coating was analyzed,and the effect of doping elements on the hardness of the coating was explained based on the d-band center theory.The accuracy of the calculation was verified by the nano-indentation experimental data.At present,the research on TiAlCrN coating mainly focuses on the preparation method of coating,and there are few studies on the optimal element ratio of elements in TiAlCrN coating.Therefore,an ideal Ti₃Al_1-XCr _XN coating model(x=0,0.125,0.25,0.375,0.5,0.625,0.75,0.875,1)was constructed based on first principles to study the effect of Al/Cr content on the properties of TiAlCrN coating.Based on the calculation method of density functional theory,the change of lattice constant of Ti₃Al_1-XCr _XN(x=0,0.125,0.25,0.375,0.5,0.625,0.75,0.875,1)coating with Al/Cr element content was analyzed,and the reason of lattice distortion was explained.The mechanical properties of the coatings with different Al/Cr content and Debye temperature were calculated to obtain the best Al/Cr ratio.In order to further explore the bonding performance between coating and substrate,the interface structure model of Ti₃Al_0.125Cr_0.875N/WC was constructed based on first principles.The surface energies of different crystal face of Ti₃Al_0.125Cr_0.875N and WC cells were calculated respectively,and the crystal faces of the interface model were determined.The convergence of atomic layer number is tested.Choosing the appropriate atomic layer number can save the calculation time effectively.Because the upper and lower surfaces of the crystal plane are different,the interface models need to be constructed respectively,and the adhesion work,interface energy and fracture toughness of the interface models are analyzed.In order to understand the bonding principle at the interface more clearly,the bonding population,state density and differential charge density at the interface are analyzed from the perspective of electronic structure,and the most stable interface structure can be obtained.In this paper,a series of detailed calculations are made on the mechanical properties of TiAlCrN uniform coating,the optimal ratio of Al/Cr elements and the bonding performance of coating with WC matrix,which provide theoretical reference for future coating research.