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The Erosion of a Cobalt-Chromium Alloy by Liquid Impact [and Discussion]

J. B. Marriott, G. Rowden, F. G. Hammitt, G. P. Thomas, A. W. O. Webb, D. Tabor, A. A. Fyall, A. Smith and J. H. Brunton
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 260, No. 1110, A Discussion on Deformation of Solids by the Impact of Liquids, and its Relation to Rain Damage in Aircraft and Missiles, to Blade Erosion in Steam Turbines, and to Cavitation Erosion (Jul. 28, 1966), pp. 144-152
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/73545
Page Count: 13
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The Erosion of a Cobalt-Chromium Alloy by Liquid Impact [and Discussion]
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Abstract

Severe erosion occurs in the leading edge of the moving blades at the exhaust end of large steam turbines. It is customary to fit a shield of some hard material such as Stellite 6 to reduce the rate of damage. Metallographic examination of specimens tested on a simulative rig showed that the erosion damage occurring was similar to that found on shields removed from service. This rig was therefore used to study the early stages of erosion in a cobalt-based alloy (Stellite 6). Specialized optical and electron metallographic techniques were used to study the microstructural changes occurring. Considerable deformation was observed in the matrix at a very early stage, without metal removal. At this time fissuring could also be seen at some carbide/matrix interfaces. As testing continued small pits were seen to form, generally adjacent to carbides. The growth of these pits was then studied. From these observations the following four-stage mechanism is proposed for erosion in Stellite 6: (1) Matrix deformation by slip. (2) Cracking at carbide-matrix boundaries. (3) Propagation of these cracks under repeated loading. (4) Intersection of crack fronts allowing material removal.

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