A study of carbon distribution on the contact zone between two solid solutions
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A Study of Carbon Distribution on the Contact Zone between Two Solid Solutions
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V.N. LNYANOI, Z.A. MATYSINA, and S.YU. ZAGINAICHENKO The diffusivity of carbon at 1273 K in solid solutions of Ni, Co, and Fe was determined by measuring the initial graphite precipitation temperature on the interface between regions of low and high carbon content during cooling. The results show that diffusivity is independent of carbon concentration for the range of concentrations investigated. When two samples of the same metal with different carbon concentrations are brought into contact and held isothermally, diffusion of carbon occurs across the contact interface between the samples from the alloy with the higher carbon content to the alloy with the lower carbon content. The resulting carbon concentration profile in the area of the interface is a function of the initial carbon concentrations, C~ and C2, the annealing temperature T, and the annealing time t. [u The present study includes the experimental determination of the carbon concentration profile and the calculation of carbon diffusivity. Carbon concentration curves were obtained by measuring the temperature at which graphite crystals were first observed during vacuum cooling on the surface of samples in the region of the interface between two samples of differing initial carbon contents, t2j The studies cover different diffusive pairs and concentrations: Ni-C (CI -- 0.17 and C2 = 0.09 mass pct C) Co-C (C~ = 0.22 and C2 = 0.08 mass pct C) Fe-C (C1 = 1.29 and C2 = 1.09 mass pct C)
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V.N. LNYANOI, Docent, and Z.A. MATYSINA, Professor, are with the Dnepropetrovsk State University, Dnepropetrovsk, 320 000 Ukraine. S.YU. ZAGINAICHENKO, Scientific Researcher, is with the Department of Physics, Dnepropetrovsk Metallurgical Institute, Dnepropetrovsk-95, 320 635 Ukraine. Manuscript submitted April 7, 1993. METALLURGICAL AND MATERIALS TRANSACTIONS B
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Fig. 1 - - Curves of the initial temperature of carbon precipitation from solid solution in different points of the contact zone.
To improve the contact, one alloy in the form of a cylinder was placed into the hole of the other one. The diffusive annealing was carried out at 1273 K during 1 hour. After annealing, the specimens were cooled at a rate of 20 K / m i n , and the initial temperature of carbon precipitation on the surface was fixed with a microscope. The optics permitted the detection of graphite crystals measuring - 5 . 1 0 -6 m . The measurements were made along the radial directions. The carbon surface segregation in carbonic alloys is well known. TM But not all of the matrix grains come out upon the observed surface by faces, favorable for graphite centers origin. Carbon does not form at some grains under the deepest supercooling, and it seems that these circumstances bring about the strong spread in determining the temperature at which solution decay begins. It does not take place because in the microscope field of view, it g
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