Grey-scale conversion X-ray mapping by EDS of multielement and multiphase layered microstructures

• Published in: Journal of microscopy (Oxford) Vol. 225; no. 1; pp. 31 - 40
• Main Authors: DAHL, K.V, HALD, J, HORSEWELL, A
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 2007
• Subjects: Compositional imaging; EDS; grey-scale conversion; layered microstructures; line profiles; spectrum imaging; X-ray mapping
• ISSN: 0022-2720; 1365-2818
• DOI: 10.1111/j.1365-2818.2007.01713.x

A procedure for grey-scale conversion of energy dispersive spectroscopy X-ray maps has been developed, which is particularly useful for the plotting of line composition profiles across modified layered engineering surfaces. The method involves (a) the collection of grey-scale elemental maps, (b) the calculation of mean grey-scale levels along strips parallel to the layered microstructure and (c) the conversion of grey-scale line profiles into composition line profiles. As an example of the grey-scale conversion method and its advantages for multielement and multiphase layered microstructures, the procedure has been applied to a layered microstructure that results from a plasma-sprayed metallic MCrAlY coating onto a nickel-superalloy turbine blade. As a further demonstration of the accuracy and amount of compositional data that can be obtained with this procedure, measured compositional profiles have been obtained for several long-term isothermal heat treatments in which significant interdiffusion has taken place. The resulting composition profiles have greatly improved counting statistics compared to traditional point-by-point scans for the same scanning electron microscope time and may be considered as a rapid alternative to energy dispersive spectroscopy spectrum imaging. The composition profiles obtained may be conveniently compared with results of multicomponent thermodynamic modelling of interdiffusion.