The High Temperature Behaviors Of Ni-Si Alloy And Its Coating In Air, Water Vapor And Supercritical Water

Ni-based alloys are considered to be the mainly key candidate compound, which couldbe used as the basic part of high-temperature structural materials due to Ni-based alloysdisplay high strength and ductility, and also show excellent oxidation and corrosion resistancein the high-temperature. However, the oxidation behaviors of Ni-based alloys exhibit variousdue to phase structure, additional element and oxidation atmosphere. Therefore, it is necessaryfor us to understand the oxidation behaviors and mechanisms of a Ni-based alloy and theanalysis is guiding significance to design the material elements and use the parts in the realcondition.The purpose of the present work is to investigate the high-temperature oxidationbehaviors and mechanisms of Ni-Si system alloy in air, water vapor and supercritical water,based on the Ni-23at%.Si alloy and the microcrystal coating with the some chemicalcomposition prepared by magnetron sputtering. The phases and figures of the oxides in thedifferent atmospheres are characterized by SEM, EDS, XRD and so on.In the high-temperature air at800,900and1000℃, the scale with duplex layer is formedboth on the substrate and coating specimens: the outer layer is large columnar NiO film; theinner is continuous protectively SiO₂film, which improve the oxidation and corrosionresistance of the alloy. Micro-crystalline enhances the selective oxidation of element Si toform the SiO₂film, especially in the high temperature.In the high-temperature water vapor in the range of600-800℃, the oxidation corrosionof substrate and coating specimens are worse. Water molecule is the primary diffusion phasein water vapor, which increase the oxidation rate shapely and enhance the formation of SiO₂film. Some displace action is occurred and no Ni/Si hydroxide form. Some spalling isobserved for the substrate specimen at800℃. Micro-crystalline accelerates the form of theprotective SiO₂film in water vapor, and improves the adherence of the scale.In the supercritical water at700℃,26MP, combined to the pure Ni specimen, thehigh-temperature oxidation progress is even worst. The phenomenon of intergranularcorrosion has found on the pure Ni specimen. The scale formed on the substrate and coatingspecimens is pore, and the thickness is beyond millimeter range.