Laser surface treatment for inhibition of metal dusting

Abstract

Metal dusting is a catastrophic carburisation phenomenon that occurs at temperatures of 450-850°C in atmospheres of high carbon activity. The resistance of alloys to corrosion, including metal dusting, relies on the formation of a dense, adherent oxide layer that separates the alloy from the corrosive environment. For such an oxide layer to be protective, it must achieve full surface coverage, be crack-free and be established before significant material degradation has occurred. Formation of a protective oxide scale can be enhanced by increasing the surface concentrations of protective elements (e.g. Cr) and by increasing the population of sites for oxide nucleation and rapid diffusion paths for the protective elements to the alloy surface.Laser surface melting has been used to try and satisfy these requirements. Laser surface melting creates a rapid solidification microstructure, that should increase the density of both oxide nucleation sites and rapid diffusion paths.The laser processing parameters have been optimised. Results of exposure to a metal dusting atmosphere (20% H2 80% CO. 650°C) are presented. Samples have been examined in plan and cross-section using optical and scanning electron microscopy. Selected samples were also examined by electron probe microanalysis.Metal dusting is a catastrophic carburisation phenomenon that occurs at temperatures of 450-850°C in atmospheres of high carbon activity. The resistance of alloys to corrosion, including metal dusting, relies on the formation of a dense, adherent oxide layer that separates the alloy from the corrosive environment. For such an oxide layer to be protective, it must achieve full surface coverage, be crack-free and be established before significant material degradation has occurred. Formation of a protective oxide scale can be enhanced by increasing the surface concentrations of protective elements (e.g. Cr) and by increasing the population of sites for oxide nucleation and rapid diffusion paths for the protective elements to the alloy surface.Laser surface melting has been used to try and satisfy these requirements. Laser surface melting creates a rapid solidification microstructure, that should increase the density of both oxide nucleation sites and rapid diffusion paths.The laser processing parameters have...