Corrosion Behavior of Hard Boride Layer Produced on Nimonic 80A-Alloy by Gas Boriding
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The gas boriding in N2–H2–BCl3 atmosphere was applied in order to produce a wear resistant surface layer on Nimonic 80A-alloy samples. The microstructure, microhardness and corrosion resistance of the boride layer were investigated. The produced layer consisted mainly of the compact boride zone (with average thickness 71 μm), including the mixture of nickel and chromium borides of high hardness (up to 1861 HV). In order to evaluate the corrosion behavior, the two methods of corrosion tests were used: potentiodynamic corrosion test in 5% NaCl solution and immersion corrosion test in a boiling solution of H2O, H2SO4 and Fe2(SO4)3. The results showed that gas boriding could provide the excellent corrosion resistance if the whole surface of a Nimonic 80A-alloy sample was covered by the continuous boride layer. Otherwise, as a consequence of selective boriding, the significant difference in electrochemical potentials caused an accelerated uniform corrosion of the base material.
KeywordsGas boriding Nimonic 80A-alloy Borides Microstructure Hardness Electrochemical corrosion resistance
This work has been financially supported by the National Science Centre in Poland as a part of the UMO-2012/07/N/ST8/03744 project. The authors wish to thank Ph.D. A. Bartkowska and M.Sc. Eng. J. Jakubowski from Institute of Materials Science and Engineering for their help and cooperation during the realization of this work.
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