The surface segregation of a Ni-Cr alloy used for commerciel heating elements hps been examined with a scanning Auger Microprobe (SAM) and other electron spectroscopy. A variety of sample surfaces prepared by different ways, including fracturing, mechanical polishing, electrochemical polishing, annealing, oxidation and their combinptions were investigated.
Results showed that on the surface treated with mechanical polishing followed by oxidation, a continuous, hichly chromium-enriched layer would be formed in a few minutes. Three factors, i.e., mechanical polishing, oxygen environment and temperature, have been found all necessary to make this Cr enrichment happen rapidly.
Taking the advantage of high spatial resolution of AMH, other experimentol facts have been obtained by comparing SFM image and Auger map. First, the Cr segregated at the area where abrading trace (about few micrometers in width) existed. Second, during the oxidation process at early stage Cr war enriched at the arrin boundaries and soreaded laterally.
These results indicate that Cr as diffusing thru the crain boundaries to the surface and the process of mechanical nolishing played, the role for increasing a large number ofcrain boundaries. The chemical driving force of oxygenalso promotes the diffusion unto at a relatively low temperature so is to complet- the orocess in a short period.