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Development of transport property-composition relationship by thermal modification of alloy composition profile
Metallic alloys develop position-dependent composition profiles specific to their thermal history, surface segregation being a long-standing example. In order to develop a systematic understanding of the most basic mechanisms for atom transport, we force an alloy specimen by thermal cycling and follow up with depth-resolved composition analyses near the specimen surface. For such studies, we make use of the new measurement methodology that facilitates simultaneous measurement of elemental composition and thermal diffusivity by time-resolved spectroscopy of laser-produced plasma (LPP) plume emissions from the specimen’s surface.We report on a new study carried out on thin ribbon specimens of 80W%Ni-20W%Cr Nichrome alloy, where paired specimens are heated for extended periods, one by AC current and another by DC current, to reach the same temperature of 1090 K. The symmetry breaking by a DC electric field applied along the length of the specimen has brought about an enriched chromium band near the surface that undulates as a function of position along the electric field axis.
Keywords: Nichrome ribbon, ohmic heating, thermal ageing, symmetry breaking, chromium enrichment, depth-resolved composition profile, atom diffusion.