First-principles Calculation Of The Surface Of Ti-Mo Alloy

With the development of ocean engineering,it is very important to develop corrosion resistant materials in recent years.β-type Ti-Mo alloy has excellent properties such as high strength,good toughness,low density,good corrosion resistance and long service life.It is a suitable Marine metal material and has a good development prospect.Corrosion mainly occurs on metal surface and it is a complex electrochemical process.Surface energy and work function are two important parameters to study surface properties.In this paper,the surface properties ofβ-Ti andβ-type Ti-Mo titanium alloys are studied by first-principles calculation method.Firstly,the surface energy and work function ofβ-Ti surface under different surface orientations,different slab model layers and different vacuum layer thickness were studied.Then,the surface properties and corrosion resistance of Mo in Ti-Mo alloy at different positions and concentrations were analyzed,and the density of states was calculated and analyzed.Finally,the surface properties of Ti-Mo-Ni allay was studied.The important conclusions are as follows:The surface calculation results ofβ-Ti and Ti-Mo alloy are as follows:（1）The calculated results ofβ-Ti surface with different crystal plane orientations show that the surface energy and work function on the densest（110）plane ofβ-Ti are in good agreement with the experimental values.The value of work function depends on the charge transfer and charge redistribution,and the value of work function depends directly on the crystal plane orientation.（2）The calculated results ofβ-Ti surface with different slab model layers and different vacuum layer thickness show that slab layers and vacuum layer thickness are important influencing factors of surface energy and work function.（3）It is found that the surface energy and work function values do not depend on the distribution of atoms on the surface layer only when Mo is doped on the surface layer.The doping position of the secondary surface layer has little effect on the surface energy and work function,and the effect of the surface layer doping on the alloy is greater than that of the secondary surface layer.（4）The surface energy and work function of Ti-Mo alloy with Mo content of8.3at.%-16.6at.%show that the surface energy of Ti-Mo alloy is larger than that ofβ-Ti,and increases with the increase of Mo content,while the surface stability decreases.The larger the work function,the stronger the corrosion resistance of the alloy.The value of work function increases with the increase of Mo content,and the corrosion resistance of Ti-Mo alloy increases.（5）Fermi level calculation shows that the Fermi level decreases with the increase of Mo content.The lower the Fermi level is,the weaker the ability to lose electrons is and the stronger the corrosion resistance is.（6）The state densities of Ti-Mo alloys with Mo content of 8.3at.%,12.5at.%and16.6at.%respectively show that the state densities of the three alloys are all greater than zero at Fermi level,indicating that they are all conductive metals.Since both Ti and Mo are d-zone transition metals,the density of the alloy states is mainly contributed by their d-orbital electrons.At Fermi level,the state density values of the three decrease with the increase of Mo content,indicating that the corrosion resistance increases with the increase of Mo content.The surface calculation results of Ti-Mo-Ni alloy are as follows:（1）The work function of Ni at different positions on the surface layer is calculated.The results show that the value of the work function does not depend on the distribution of atoms on the surface layer.（2）The work function of the Ti-Mo alloy doped with different Ni content was calculated.The results show that the corrosion resistance of the alloy can be improved by doping appropriate Ni.The work function of Ti₄₀Mo₇Ni alloy is the largest,which is larger than that of Ti-Mo alloy,indicating that Ti₄₀Mo₇Ni has strong corrosion resistance.（3）The state density of Ti-Mo-Ni alloy was calculated.The results show that the state density values of Ti₄₃Mo₄Ni,Ti₄₀Mo₆Ni₂,Ti₄₀Mo₇Ni alloys have obvious metal conductivity.Since both Ti,Mo and Ni are d-zone transition metals,the density of the alloy states is mainly contributed by their d-orbital electrons,while s and p orbitals have little influence.The pseudoenergy gap of Ti₄₃Mo₄Ni is obvious,so it has the strongest covalence and stability.The covalence and stability of Ti₄₀Mo₆Ni₂and Ti₄₀Mo₇Ni weakens successively.It is found that Ti₄₀Mo₇Ni have the lowest state density and the best corrosion resistance by observing the total state density at Fermi level.