First-Principles Simulation Of He-Induced Damage And Irradiation Defects In MAB Phases

Similar to M_n+1AX_n（MAX,M:transition metal,A:A group element,X:C or N,n=1～3）phase materials,MAB（M:transition metal,A:A group element,B:B）phases also exhibit excellent comprehensive mechanical and thermal properties that are applicable to future nuclear reactors.There are a lot of researches about the intrinsic properties of MAB phases.There also exists some researches about their antisite/amorphization resistance under irradiation.However,the helium-induced embrittlement property of MAB phases is still unknown.Through first-principles theory,the authors firstly constructed MAB phase lattice models including point defects.In addition,the authors demonstrated the reliability of the models and the simulation methods through comparing the calculated lattice constants and the experimental values.Furthermore,the origination and growth conditions of He bubbles under irradiation in MAB phase MoAlB and Fe₂AlB₂,the intrinsic point defects and He bubble formation conditions of WAlB and the He bubble resistance properties at the Zr/MoAlB and the Zr/WAlB interfaces have been calculated in this thesis.The He bubble resistance properties in the above three works are predicted through the calculation of the single/double vacancy formation energies to simulate the possible He bubble number density and the calculation of the trapping energy of He atoms by different vacancy sites and the 2^ndprimary nearest vacancy formation energies to simulate the probable He bubble shape and average sizes.The main results of this work are as following:1)The He bubble resistance and antisite/amorphization resistance of MoAlB and Fe₂AlB₂present contrary trend.When considering the probable He bubble number density and cracking resulted from the anisotropic formation of He bubbles Fe₂AlB₂possesses better properties than MoAlB.2)In WAlB V_Aland V_Bvacancy as well as W_Aland B_Alantisite presents low formation energy,which is highly possible to reflect a high amorphization tendency of WAlB under the irradiation environment.And at the same time WAlB presents not very outstanding He bubble resistance property based on the judging indictors of the single vancancy formation energy,the He atom trapping number and the further 2^ndprimary nearest vacancy formation energy.3)In the six respectively types of Zr/MoAlB and Zr/WAlB interfaces,Al-2/B-2/Mo-2 type Zr/MoAlB interfaces and W-2 type Zr/WAlB interface have better He bubble resistance property based on the judging indictors of the single vancancy formation energy and the He atom trapping number.These three works can provide foundation for the embrittlement tendency predictive model of the MAB phase materials MoAlB,Fe₂AlB₂and WAlB and their interfaces with the Zr alloy under the irradiation environment.