First-principles Study On Intermetallic Compounds And Interfacial Properties Of Aluminum-copper Alloys

The Al-Cu alloy is mainly used in aerospace,marine industry,national defense industry,precision instruments and other fields.With the development of science and technology,the requirements of material properties are increasing and the research on Al-Cu alloy is deepening.In order to design and develop Al-Cu alloy materials with more excellent comprehensive properties,we should not only improve the mechanical properties,physical properties and chemical properties of the materials,but also pay attention to its internal microstructure,especially the intermetallic compounds in this kind of alloy.The stability and mechanical properties of these alloys are complicated to measure by experimental method,but they are not constrained by time and space through computer simulation.However,according to the interaction between nuclei and electrons in crystals and their motion laws,first-principles methods can obtain data on the properties of compounds as long as the crystal structure model of the material is known and parameters such as temperature and pressure are set.Therefore,it is of great significance to conduct first-principles research on intermetallic compounds and their interface properties in Al-Cu alloys.Based on density functional theory,the stability,elastic properties and electronic structure of Al-Cu,Al-La binary intermetallic compounds and B2-Al Cu doped by transition metal elements have been studied by first-principles method.Also,the interface properties of Al₂₀Ti₂La(100)/Al(100),Al₂₀Ti₂La(110)/Al(110)and Al₂₀Ti₂La(111)/Al(111)under different stacking models were investigated.The results of this study provide a theoretical basis for improving the properties of intermetallic compounds and for the research of high-performance Al-Cu alloy materials.The main achievements are as follows:(1)The phase stability,elastic properties and electronic structure of Al-Cu binary intermetallic compounds were studied.The results show that all Al-Cu binary intermetallic compounds are thermodynamically stable,among which Al Cu-m I20,Al Cu-m C20 and Al₄Cu₉-c P52 are the most stable compounds.The Al₄Cu₉-c P52 has the strongest shear deformation resistance and rigidity,on the contrary,Al Cu-c P2 displays the weakest shear deformation resistance and rigidity.The seven compounds,such as Al₃Cu-t P8,Al₃Cu-c P4,Al₂Cu-t P3,Al₃Cu₂-h P5,Al Cu-m C20,Al Cu-m I20 and Al₄Cu₉-c P52,were brittle,while the others were plasticity.These Al-Cu binary intermetallic compounds have complex chemical bond structure because they contain both metal bond and covalent bond properties.According to the analysis of the Debye temperature,among these Al-Cu binary intermetallic compounds,the Al₂Cu-t P3 shows strong atomic binding force,while the Al Cu-c P2 presents the weakest atomic binding force.(2)The phase stability,elastic properties,work function and electronic structure of Al-La binary intermetallic compounds have been studied.The results indicate that all Al-La binary intermetallic compounds are thermodynamically stable.The alloying ability of eight intermetallic compounds from strong to weak is Al₂La,Al La,Al₃La,Al₁₁La₃,?-Al₄La,?-Al₄La,Al La₃(P6₃/mmc)and Al La₃(Pm-3m).The Al₃La appears the strongest shear deformation resistance and stiffness.The Young's modulus and Vickers hardness of Al-La compound are correlated with the sixth power of the work function.These compounds all have metallic properties,and the presence of a small amount of charge transfer in the compounds indicates the properties of metallic bonds.There is a large amount of charge aggregation between Al atoms,which suggests the existence of the covalent Al-Al bond.On the basis of the calculation results of Debye temperature,the order of binding force between atoms of Al-La intermetallic compounds from strong to weak is:Al₃La>Al₁₁La₃>?-Al₄La>Al₂La>?-Al₄La>Al La>Al La₃(Pm-3m)>Al La₃(P6₃/mmc).(3)The effects of transition element substitution on the mechanical properties and electronic structure of B2-Al Cu compounds were predicted.It is found that Zn,La and Hg atoms exhibit a weak Al site preference,and Cd atoms display a strong Al site preference.However,Sc,Y and Ag atoms reveal a weak Cu site preference,while other transition metal elements have a strong Cu site preference.The thermodynamic properties of all the doped compounds are stable.The Al₈Cu₇Fe,Al₈Cu₇Ru and Al₈Cu₇Os are the compounds with the highest compressive resistance in these three cycles.Nevertheless,the Al₈Cu₇Fe,Al₈Cu₇Tc and Al₈Cu₇Re are the compounds with the strongest shear deformation resistance and the most rigid among the three cycles,respectively.Compared with the undoped alloy,the mechanical properties and Vickers hardness of the alloy with transition metal elements are improved.The exploration of the electronic structures of Al₈Cu₇Fe,Al₈Cu₇Tc and Al₈Cu₇Re demonstrates that metal bond and covalent bond are mixed,and the covalent bond between Cu and Fe(Tc,Re)is not strong.(4)The interface properties of Al₂₀Ti₂La(100)/Al(100),Al₂₀Ti₂La(110)/Al(110)and Al₂₀Ti₂La(111)/Al(111)under different stacking models were investigated.The results exhibit that the surface energy converges when the atomic layer is 7 in three different surface models constructed by Al and Al₂₀Ti₂La respectively.Among the three different interfaces,Al₂₀Ti₂La(100)/Al(100),Al₂₀Ti₂La(110)/Al(110)and Al₂₀Ti₂La(111)/Al(111),the central-site stacking mode has smaller interface spacing,larger binding energy and better interface stability.Under the three central stacking modes,the interface spacing of Al₂₀Ti₂La(110)/Al(110)interface is the smallest and the binding energy is the largest,so the interface stability is the best.In the Al₂₀Ti₂La(110)/Al(110)interface structure,the Al slab and the Al₂₀Ti₂La slab present metal bond and obvious covalent bond characteristics,respectively.There are obvious covalent bonds between Al and Al₂₀Ti₂La atoms at the interface.The Al₂₀Ti₂La plays a role of heteronucleation in?-Al,which is beneficial to the grain refinement of?-Al.