Corrosion Behavior of Hard Boride Layer Produced on Nimonic 80A-Alloy by Gas Boriding

摘要

The gas boriding in N-2-H-2-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 mu m), 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 Fe-2(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.