First-principles Study Of The Effects Of Chrome And Vanadium Doping On The Performance Of Tungsten

Inertial confinement fusion(ICF)is generally considered as one of most potential solutions to solve the energy shortage the world will face in the future.Tungsten is widely considered as the most potential plasma-facing material(PFM)and first wall material(FWM)due to its high melt point,good thermal conductivity,low sputtering rate and other excellent properties.Tungsten is considered as the PFM used in the international thermonuclear fusion experiment reactor(ITER)and China fusion engineering test reactor(CFETR),and other fusion reactors.In fusion reactor,tungsten subjects to low-energy high-current hydrogen and helium particles,and these two particles unavoidably result in some disadvantageous effects on the performance of tungsten when they enter the tungsten.If a large amount of hydrogen to helium atoms accumulated in tungsten,and hydrogen bubble or helium bubble are formed,the result of this phenomenon is the tungsten service life shorten a lot.When hydrogen and helium accumulated in tungsten surface that face to fusion plasma,the results are the tungsten surface blister and fuzz,this will make impurities enter the fusion plasma,and it has a serious influence on the stable operation of the fusion reactor.Usually,there are a lot of high-energy fusion neutrons in fusion reactor,vacancy and self interstitial atoms(SIAs)are generated in tungsten due to the neutrons radiation.So studies on the behavior of hydrogen and helium in tungsten,the interaction between hydrogen or helium and SIAs are very important for the development of the tungsten-based plasma face materials.The mechanical properties of tungsten are improved when adding some alloy elements in it,the alloy atoms will become nucleation center for hydrogen and helium,so hydrogen and helium are transported to a suitable place and deposition,the service life of tungsten is greatly extended.The behavior of hydrogen and helium in tungsten,the interaction between hydrogen or helium and vacancy in tungsten,the mechanism of the nucleation of hydrogen bubble and helium bubble in tungsten,the effect of chrome and vanadium on the mechanical properties,and the interaction between chrome or vanadium and hydrogen or helium in tungsten were investigated by using first-principles calculation based on the density functional theory in this paper,and the results are as follows:1.For a single hydrogen atom,the energetically favorable site is the tetrahedral interstitial site while the substitutional site is the most preferred site for a single helium atom,because the formation energy of hydrogen and helium that are located in these position are the minimum.2.There is a strong attraction interaction exist between vacancy and hydrogen or helium in tungsten,a vacancy can attracts 12 hydrogen atoms or 14 helium atoms,the reason for the attraction interaction exist between vacancy and hydrogen is the lo cal stress caused by vacancy,local stress and the decrease of electron density make a great contribution to the attraction between vacancy and helium.3.Vacancy plays an important role on the nucleation of hydrogen atoms and helium atoms in tungsten.When a cluster,which include hydrogen or helium atoms and vacancy,is formed in tungsten,the stability of the nearest neighbor tungsten atoms around the cluster deceased quickly,and a new vacancy is formed near the cluster and the vacancy will attracts hydrogen and helium in tungsten,the hydrogen bubble and helium bubble are growing until the bubbles are broken under the help from vacancy.4.The adding of chrome and vanadium will make the mechanical strength of tungsten decrease and the ductility of tungsten increase,the reasons for these changes are the strength of W-V bond and W-Cr bond smaller than that of W-W bond.5.There is an attraction interaction exists between chrome or vanadium and hydrogen or helium in tungsten,and the strength of the attraction is determined by the position of hydrogen and helium.The attraction between chrome or vanadium and hydrogen or helium is smaller than the attraction between vacancy and hydrogen or helium,and the reason is the local stress and electron density decrease that caused by chrome or vanadium smaller than that caused by vacancy.These computational results might provide a clear understanding of the behavior of hydrogen and helium in tungsten,the interaction between vacancy and hydrogen or helium,the mechanism of the nucleation of hydrogen atoms and helium atoms,the effect of chrome and vanadium on the performance of tungsten,and the interaction between chrome or vanadium and hydrogen or helium from a atomic le vel.Our results also might shed some light on the development of the W-based plasma facing materials that used in ITER,CFTER and other fusion reactors.