First Principles Study On The Effect Of 4d Transition Elements On The Plasticity Of γ-TiAl Alloy

The term "metal" usually refers to substances that have distinctive metallic structures and components.Metal is a variety of materials,including pure metal,synthetic metal(alloy)and special metal materials.Metals are an important part of human society and they have witnessed our progress and development.Metal materials are widely used in everyday life,from small to large,in the manufacture of machine parts,and even aircraft,missiles,rockets and satellites.As a new type of metal compound material,TiAl alloy has many advantages,including low density,high specific strength and elastic modulus,and high oxidation resistance at high temperature,so it has been widely used in automotive and aerospace fields.Therefore,the study of TiAl alloy is of great significance.However,due to its poor plasticity at room temperature,it is difficult to process,which seriously affects the development of TiAl alloy.Therefore,the study of plasticity improvement of TiAl alloy is the main aspect of the study of TiAl alloy.Through a lot of experiments,researchers found that the room temperature plasticity of TiAl alloy can be effectively improved by doping a certain amount of the third alloying element.However,due to the complexity and high cost of experimental operation,the cost of numerical simulation is relatively low,only need to carry out simulation and data processing on the computer.In addition,the experiment can only collect data from specific points,while the numerical simulation method has a wide range of data collection,making up for the shortcomings of the experiment.Reasonable numerical simulation method can also provide theoretical guidance for experimental research.As a calculation method based on density functional theory,the first principle calculation method is commonly used to calculate and analyze the properties of alloys.VASP software package is one of the most widely used commercial software in the scientific research of material computing simulation.It is based on density functional theory to calculate the first-principles electronic structure of material systems.VASP software package can calculate structural parameters,thermodynamic properties,electronic properties,magnetic properties and other properties of materials,with very powerful computing function.Many researchers at home and abroad have calculated the effect of γ-TiAl doped with the third element on its formation enthalpy,elastic constant,elastic modulus and state density by using the first principles calculation method.The plasticity of γ-TiAl was studied when doped with 4d transition metal element.Therefore,in this paper,the first principle method is used to investigate the change of formation enthalpy,cell volume,elastic modulus,state density and other physical quantities of γ-TiAl alloy doped with 4d transition metal elements at different doping concentrations.Furthermore,the effect of 4d transition metal element doping on the plasticity of TiAl alloy was analyzed.The results are as follows:(1)The formation enthalpy,elastic constant and elastic modulus of γ-TiAl cell were calculated by geometric optimization.The results show that γ-TiAl cell is stable and plastic.(2)The formation enthalpy,cell volume,elastic constant and elastic modulus ofγ-TiAl doped with 4d transition metal were calculated.The results show that Tc,Ru,Rh,Pd of the 4d transition metal elements have a strong ability to improve the plasticity of γ-TiAl,followed by Nb and Mo,Y,Zr,Ag and Cd have a poor effect,and the effect is most obvious when Ru atom replaces Al atom doped with γ-TiAl.By analyzing the density of states,it is found that when Ru atom replaces Al atom doped with γ-TiAl,the interaction between Ti-Ru will be enhanced,which will weaken the interaction between Ti-Al in γ-TiAl,and thus enhance the plasticity of γ-TiAl.(3)The effects of γ-TiAl and β-TiAl phases doped with Ti and Mo substituting with Al were calculated on the formation enthalpy,cell volume,elastic constant and elastic modulus of γ-TiAl and β-TiAl phases at different doping concentrations.The results show that the phase transition from γ phase to βphase occurs when the doping concentration reaches 12.5 at%.Through the analysis of each doping system and Poisson’s ratio,it is found that when Mo atom replaces Al atom doped with β-TiAl,the plasticity is strongest at the doping concentration of12.5 at%.When Mo atom replaces Ti atom doped with γ-TiAl,the plasticity is strongest at the doping concentration of 25 at%.However,due to the poor stability of the system at this time,So it is considered that when Mo atom replaces Al atom doping β-TiAl alloy,the plasticity of TiAl alloy is improved best when the doping concentration is 12.5 at%.