First-principles Study On Effects Of Aluminum On Structure And Mechnical Properties Of Ni/Cr₂O₃Interface

Relying on excellent oxidation resistance, nickel alloys become one of important high-temperature materials, which play a unique role in the fields of defense and industry and are widely used as high temperature parts in aerospace, petrochemical industry, electric power and underwater operation. Recently, a mass of experimental investigations affirm that the prominent oxidation resistance of nickel alloys results from the compact multi-layer oxides which are formed on the surface of metal. By employing characterization methods, these researches confirm that the complicated oxide film contains NiO、Cr2O3、Al2O3and spinel oxides. However, microscopic formation mechanism and essential reasons for the surface multilayer oxide film of nickel alloys have not been explicitly explained in these investigations.On the basis of experiment results, we should make integrated analysis from the theory perspective of microscopic formation mechanism and mechanical properties for surface oxide film on nickel alloys by employing the first-principles method. First, by comparing atomic structure and adhesion properties for different Ni(111)/Cr2O3(0001) configurations the most stable alloy/oxide construction was determined. And based on this configuration, the diffusion pathway of Al atoms at the Ni/Cr2O3interface is further studied. The results indicated that Al atoms originating from Ni slab prefer to diffuse into Cr2O3slab through the Ni/Cr2O3interface by taking the place of Cr atoms to form chemical bonds with O atoms which results in the formation of Al2O3at Ni/Cr2O3interface. This conclusion showed that the formation of Al2O3oxide at interface is resulted from the diffusion and segregation of the internal Al atoms. Furthermore, the stable Ni/Al2O3/Cr2O3multilayer oxide film will appear as the Al segregation at Ni/Cr2O3interface, which will explain the experimental phenomena that why the outer oxidized scale of Ni based alloy is Cr2O3, while the inner oxidized scale is A12O3. The investigation elucidated the formation and growth mechanism of surface multilayer oxide film of nickel alloys from a microelectronics view. The diffusion of Al atoms results into the formation of compact multi-layers oxides scale that prevents O atoms from further spreading into the matrix, which makes a great contribution to the excellent high-temperature oxidation resistance of Ni based alloy.Furthermore, the interfacial adhesion between oxide film and matrix alloy has a great influence on antioxygenic property and service life. Therefore, the damage of uniaxial tensile stress to metal/oxide interface structure with different crystalline orientation is discussed in this paper by employing first-principles calculation. This simulation attempts to discuss the interface adhesion and reveal the reasons of oxide film failure mechanism under practical force condition from the microscopic view. Researches showed that for the Ni/Cr2O3structure with [1-10]//[11-20] orientation relationship, due to the high strength of Cr2O3and Ni/Cr2O3, tensile stress results, and first of all, in the Ni deformation. When the Ni part deforms to a certain degree, the enhancement of Ni strength will lead to the propagation of crack tip at Ni/Cr2O3interface till the structure completely fractures. By comparison of interfacial tension with different crystalline orientation, it was proved that the appropriate crystalline orientation can improve the adhesion of interface structure and the formation of Al2O3oxide also makes a contribution to the improvement of Ni/Cr2O3interface adhesion.