First Principles Of Selective Laser Melting Forming Of Ti48Al2Cr2Nb Alloy And Friction Performance Research

With the stable and orderly deployment of the manned lunar landing project,higher requirements are placed on the engines of new aerospace vehicles.As a new high-temperature material,Ti48Al2Cr2Nb alloy has the advantages of high melting point,low density,high specific strength,high high-temperature strength,and creep resistance,becoming one of the most promising materials in the aerospace field in various countries.However,Ti48Al2Cr2Nb alloy has low ductility,and traditional forming methods are difficult to carry out plastic deformation and form complex structures,which restricts the development of Ti48Al2Cr2Nb alloy.Selective laser melting forming（SLM）solves the difficult problem of forming precision complex parts by slicing and layering,and laying powder layer by layer for melting and forming.It has the advantages of short cycle and can be arranged in any structure.In this study,the Ti48Al2Cr2Nb alloy was formed using SLM forming technology.The material properties of the basic phasesα₂-Ti₃Al andγ-TiAl in the Ti48Al2Cr2Nb alloy,their crystal relationships,and interfacial bonding mechanisms were simulated using first principles.The friction and wear properties of the Ti48Al2Cr2Nb alloy were investigated.The main research contents and conclusions are as follows:（1）The elastic modulus and anisotropic characteristics of the basic phasesα₂-Ti₃Al andγ-TiAl in the SLM formed Ti48Al2Cr2Nb alloy were calculated.The results show that the Poisson’s ratio ofα₂-Ti₃Al phase is higher,and the Young’s modulus and shear modulus are lower.That is,the SLM formed Ti48Al2Cr2Nb alloy contains a large amount ofα₂-Ti₃Al phase,which is the main reason for its brittleness.Bothα₂-Ti₃Al andγ-TiAl have obvious anisotropic characteristics,and it is necessary to regulate the interfacial binding orientation of the internal phases during the preparation of Ti48Al2Cr2Nb alloys.（2）The interfacial strength betweenα₂-Ti₃Al andγ-TiAl was calculated.Five representative low index surfaces（001）,（100）,（011）,（110）,and（111）of TiAl were selected to establish an interface model withα₂-Ti₃Al low index surface（0001）,respectively.The interfacial binding work,interfacial energy,charge density,and density of states of the five interface structures were calculated.The results show that theγ-TiAl（111）/α₂-Ti₃Al（0001）interface model has a smaller mismatch degree and the highest interfacial bonding strength.Among them,the Ti center-ST interface model has the largest interfacial binding work and the smallest interfacial energy.The Ti and Al atoms at the interface have charge transfer and orbital hybridization phenomena,forming relatively stable metal bonds,which is conducive to the stability of the interface.（3）The formation energy and elastic constants of alloying elements（Cr,Nb）doped with the main phasesα₂-Ti₃Al andγ-TiAl were studied using the virtual crystal approximation method.The results show that both Cr and Nb are easy to replace the Ti atoms inα₂-Ti₃Al andγ-TiAl,and Nb is more likely to replace than Cr.In theα₂-Ti₃Al system,the doping of Nb atoms gradually reduces the bulk modulus,Young’s modulus,and shear modulus as the substitution ratio increases,while the Poisson’s ratio increases.However,with the doping of Cr atoms,the elastic constants all exhibit extreme values.In theγ-TiAl system,with the increase in the proportion of element doping,the elastic constant exhibits an extreme value when doped with Cr atoms,while the elastic constant generally exhibits an upward or downward trend when doped with Nb atoms.（4）The interfacial bonding strength between TiAl（111）/Ti₃Al（0001）doped with alloy components（Cr,Nb）was studied.The results show that Cr and Nb are easy to replace Ti atoms at the interface.The binding work,segregation enthalpy,and charge density differences of the interface under four doping systems are compared.It is found that the interface model doped with Cr and Nb is beneficial to improving the bonding strength of the interface and facilitating interface stability.（5）The effects of different rotational speeds on the friction properties of Ti48Al2Cr2Nb alloy formed by SLM and samples after hot isostatic pressing were experimentally investigated.The results show that,as the rotational speed increases,the wear rate of Ti48Al2Cr2Nb alloy decreases,and the friction coefficient gradually decreases.This is due to the formation of a mechanical mixing layer,which reduces the contact area between the friction material and the wear surface,and improves the tribological properties.After HIP treatment,the wear rate is significantly reduced,and some large flaky wear debris appears on the wear surface.After HIP treatment,the hardness of the material increases,and it has strong wear resistance and cutting resistance.However,its internal crystal structure is relatively dense and orderly,making it difficult to undergo plastic deformation and prone to brittle fracture.