(753a) High Throughput Study of Alloy Surface Oxidation Across Composition Space: AlxFeyNi1-x-Y

Comprehensive study of the interfacial phenomena of alloy materials, A_xB_yC_1-x-y, across composition space is hampered by the fact that the study must span a multidimensional and continuous composition space, x = 0 -> 1 and y = 0 -> x.  Traditional methods of study require the preparation and characterization of large numbers of samples of single composition.  This can be circumvented by high throughput methods that use Composition Spread Alloy Films (CSAFs) as platforms or libraries of alloy composition.  CSAFs are thin alloy films deposited onto substrates in such a way that there is a gradient in their composition across the surface.  As such they can contain all possible compositions of a ternary alloy, A_xB_yC_1-x-y with x = 0 -> 1 and y = 0 -> x.  Spatially resolved methods for characterizing the CSAF can then be used to determine bulk composition, surface composition, phase, electronic structure, etc. as functions of position on the substrate, i.e. as functions of alloy composition, with arbitrarily high composition resolution.  We demonstrate the utility of the CSAF methodology for study of alloy interface properties through a study of the surface oxidation of Al_xFe_yNi_1-x-y superalloys used as turbine materials for electrical power generation.  The critical problem is to understand the role of Al in prevention of alloy oxidation by formation of a passivating layer of Al₂O₃ at the alloy surface during exposure to air.  Using a Al_xFe_yNi_1-x-y and a combination of energy dispersive x-ray spectroscopy and depth profiling using x-ray photoelectron spectroscopy, we have been able to map the Al concentration boundary in Al_xFe_yNi_1-x-y above which the alloy is passivated.  Along the AlNi binary, the passivation is caused by the formation of a surface layer of Al₂O₃.  Along the AlFe binary, one can discern two regions of behavior, one in which the passivating layer is at the surface and the other in which the passivating layer is formed in the subsurface region beneath a layer of Fe₂O₃.  Mapping these oxidation resistance boundaries across alloy composition space would be impossible without the high throughput CSAF methodology.