| As an ideal energy,nuclear fusion energy has attracted considerable attentions all over the world.However,nuclear fusion reactor works with the complicated environment have put forward stringent requirement for materials in fusion reactors.One of the most critical issues of fusion energy is the first wall material of facing high temperature plasma,i.e.Plasma Facing Materials(PFMS).Tungsten metal is considered to be one of the most promising candidates for plasma facing materials(PFMs)due to its high melting point,high strength at high temperature,high sputtering threshold energy,good thermal conductivity,low thermal expansion coefficient,low tritium retention and high resistance to plasma erosion and so on.Unfortunately,pure tungsten metal exhibits poor radiation stability and fracture toughness,low ductility associated with a high ductile-to-brittle transition temperature(DBTT).In particular,the intrinsic impurities(C,N,O)and the transmutation products(H,He,D,T)enters tungsten material,and it serious effect the mechanical properties and the structural strength of tungsten.The doping of alloying elements can decrease the ductile to brittle transition temperature and improve the recrystallization temperature,which can improve the performance of tungsten metal.Using the first-principles methods,this paper studied the effect of rare earth elements(Y,Ti,Ta)on mechanical properties of tungsten.The relationship between the elastic constants,elastic modulus,Poisson's ratio and Cauchy pressure with the properties of the material is discussed.At the same time,and studied the effects of titanium alloying tungsten on C,H impurities incorporation,respectively.The interaction mechanism between carbon and hydrogen with the lattice of tungsten alloy is discussed.Through the design of the composition and structure of tungsten alloy materials,a new type of tungsten alloy with superior properties can be prepared.Based on the density functional theory(DFT),the mechanical properties of part W alloys(doping Y,Ti and Ta)were studied by the first principles method and the effects of binary W-Ti alloy on the interference of C and H impurities were also studied.The results show that the rare earth elements Y,Ti and Ta are all reduced the mechanical strength of W metal materials in the W lattice.However,the ductility of all W alloy materials has been improved obviously.When the Y concentration reaches 0.25,the deformation resistant and ductility of W-Y alloy are largely enhanced.It is shown that Ti alloying in bcc W lattice is thermodynamically favorable when the Ti concentration is lower than 25% and the W0.8125Ti0.1875 have the lowest formation energy.Although the mechanical strength of the W-Ti alloys is lower than that of pure W metal,it is much higher than that of pure Ti metal.On the other hand,the ductility of W-Ti alloys is much higher than that of pure W,and even higher than that of pure Ti,indicating that Ti alloying can improve the ductility of bcc W substantially.It is shown that Ta alloying in bcc W lattice is an infinite solid solution and the W0.5Ta0.5 have the lowest formation energy.Although the mechanical strength of the W-Ta alloys is lower than that of pure W metal,it is much higher than that of pure Ta metal.On the other hand,the ductility of the W-Ta alloys is much higher than that of pure W,and even higher than that of pure Ta,indicating that Ta alloying can also improve the ductility of bcc W substantially.In the W-Ti lattice,the single C atom is energetically most favorable sitting at the octahedral interstitial site(OIS)nearest neighboring to the Ti atom and the minimum solution energy is about 0.874 eV.The single H atom is energetically favorable sitting at the tetrahedral interstitial site(TIS)nearest neighboring to the Ti atom and the minimum solution energy is about-0.606 eV.It is shown that the effect of titanium doping tungsten on the C,H impurity migration behavior is small,while the C impurity migration energy barrier is quite high,and the highest energy barrier is up to 1.600 eV.The H impurity energy barrier is about 0.186eV~0.206 eV.Base on the elastic constants analysis,titanium-doped tungsten can withstand the degradation of mechanical strength induced by C,H impurities.On the other hand,it is found that the ductility of pure W metal and W-Ti alloys can be improved substantially by C,H impurities.However,the effect of the improved ductility is more obvious in bcc pure W metal than that in the W-Ti alloys.In addition,substitutional C atom is better than interstitial C atom in terms of enhancing the ductility of pure W.These results provide a guiding role for the further optimization of the composition of W alloy,which is helpful to understand the interaction between C,H impurity and W-Ti lattice,and also provide a useful resource library for the study of plasma facing materials... |
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