A method to quantitatively analyze the surface regions of metals, alloys, and coatings using proton-excited X-ray emission (PEX) has been utilized in two areas of metallurgy research. This paper describes application of the technique to (1) the development of erosion- and corrosion-resistant coatings, and (2) the study of structural failures in turbine alloys.
The technology for the electrodeposition of erosion- and corrosionresistant TiB2 coatings from molten-salt electrolytes has been developed in order to provide protective coatings for valve components in coal gasification plants. Analyses by PEX and X-ray diffraction have played the key role in the determination of the optimum electrolysis parameters required to obtain adherent, erosion-resistant TiB2 coatings. From these studies, the erosion resistance of a TiB2 coating can be predicted on the basis of (1) the amount of Cr and Fe impurities codeposited during electrolysis and (2) the degree of orientation of the TiB2 crystal structure along the (110) or (100) planes.
PEX was used for analytical studies of a Nimonic 105 alloy turbine blade and an A-286 alloy turbine wheel from a San Diego, California, power generating station gas turbine that suffered a catastrophic failure in November 1974. Analyses of the turbine blade in the region at which the rupture occurred showed alloy composition changes that included decreases of 80%, 78%, 52%, and 50% of Al, Ti, Cr, and Co, respectively, and an increase of 2500% in Fe. Alloy composition changes were also found at the failure interface of the turbine wheel; these included decreases of 43%, 21%, and 15% in Hi, Cr, and Ti, respectively, and increases of 248% and 714% in Si and Al, respectively.