First Principle Simulation Of Ni₃Al Oxidation At The Early Stage

Ni-Al superalloys are a class of important intermetallic materials with high melting point,low density,good oxidation and corrosion resistance.These excellent properties make the Ni-Al superalloys widely studied.As a typical Ni-Al superalloys,Ni3Al has a broad application prospect in aerospace,electric power,metallurgy and many other industries.Ni3Al has good oxidation resistance,the traditional study of metal oxidation mainly focuses on the growth behavior of oxide in the later stage of oxidation,but little research has been done at the early stage of oxidation.Thus,we apply ab initio calculations based on density-functional theory and thermodynamics calculations,build atomic oxidation models of Ni3Al at the early stage,and explore the oxidation mechanism of Ni3Al at the early stage and the growth rule of oxide during Ni3Al oxidation,in order to establish theoretical foundations for controlling metal oxidation at atomic level.Several innovative conclusions are drawn as follows.(1)Comparing the relative surface energies of the clean Ni3Al(100)and Ni3Al(110)surfaces with different surface antisite defects as functions of the chemical potential of Al,we find that the perfect surface is the most stable configuration for the Ni3Al(100)surface,whereas A1 antisite defects tend to segregate at the Ni3Al(110)surface under the nonoxidizing conditions.We construct the surface phase diagrams for the O-Ni3Al(100)and O-Ni3Al(110)surfaces with different antisite defects under different oxygen coverages.The surface phase diagrams show that the oxygen adsorption enhances the Al surface segregation,resulting in the formation of a complete A1 surface layer at the initial stage of oxidation.Compared with the stable configuration after oxidation,the Ni3Al(100)surface is thermodynamically more favored to oxidize completely at a lower oxygen coverage.(2)For the Ni3Al(100)surface oxidation at the early stage,the substrate first has the Ni and Al antisite defect and then has the Ni vacancy,while for the Ni3Al(110)surface oxidation at the early stage,the substrate first has the Ni vacancy and then has the Ni and Al antisite defect.From the energy barrier figure of Ni3Al(110)surface,we find that the absorption of O atoms imporve the energy barrier of the Al atom and the Ni atom,which has a great impact on the Ni atom.At the same time,we conclude that the oxidizing reaction is an exothermic reaction,and the absorption of O atoms reduce the system energy,which has a great impact on the Al atom.