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Long-Time Oxidation of gammaFe and LH15 Steel at High Temperatures in Air
Kučera, Jaroslav ; Adamaszek, K. ; Jurasz, Z.
The results of surface oxidation and decarburizatin of (Fe, C, Mn, Si, Cr, Ni) steels are reported. The oxidation anneals were carried out at temperatures T = 940, 980, 1020, 1060, 1100 oC. The time course of Fe and of steels oxidation is expressed by parabolic law. The surface oxidation is accompanied by decarburization of surface steel layers. The evaluation of measured carbon concentration profiles N(C,x,t) yields diffusion coefficients D(C,T). Oxidation coefficients kp(T) are linearly proportional to D(C,T).
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Diffusion of Ni and Ga along High-Diffusivity Paths in polycrystalline Ni3Ga
Čermák, Jiří ; Rothová, Věra
The volume and grain boundary (GB) diffusion of 63Ni and 67Ga radiotracers in polycrystals of Ni3Ga intermetallic was studied in the vicinity of stoichiometric composition A3B (23.5 - 28.3 at. % Ga). Both volume- and GB diffusivity was measured in the temperature interval 773 - 1373 K by residual activity method. Obtained Ga volume diffusivity increases with increasing Ga concentration x(Ga); the increasing tendency of Ni volume diffusivity with increasing x(Ga) is pronounced especially at lower temperatures. GB diffusivity of both Ga and Ni in Ni3Ga are close one to another and contrary to diffusion behavior of components in Ni3Al - they do not show any significant dependence on x(Ga).
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Comparison of Al/Ni and Co/Ni Interdiffusion Coefficients in Pseudobinary Sections of Ni3Al-Co alloys
Gazda, Aleš ; Rothová, Věra ; Čermák, Jiří
Interdiffusion in Ni3Al intermetallic alloyed by 0 - 19 at % Co was studied in three pseudo-binary sections: c(Al) = 22, c(Co) = 3.5, and c(Co) = 16 (c in at. %). The experiments were carried out at temperatures between 900 and 1200°C. Since no detectable shift of tungsten inert markers was observed, it was concluded that the intrinsic diffusivities of element pairs with varying concentration (Al/Ni and Co/Ni) in respective pseudo-binary sections are approximately equal one to another. The interdiffusion in pseudo-binary alloys Al/Ni (c(Co) = const.) runs slightly faster than that in pseudo-binary alloys Ni/Co (c(Al) = const.). The relations between the measured interdiffusion coefficients in the Ni3Al-Co ordered gamma prime phase agree well with literature data for the interdiffusion coefficients in both pure gamma prime and Co alloyed gamma prime phases and also for the disordered Al-Ni and Co-Ni solid solutions. They are qualitatively explained by interaction between constituents and/or by their interaction with vacancies.
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OXIDATION OF Fe AND STEELS AT HIGH TEMPERATURES
Kučera, Jaroslav ; Adamaszek, K. ; Hajduga, M.
The results of surface oxidation and decarburization of (Fe, C, Mn, Si, Cr, Ni) steels are reported. The oxidation anneals were carried out at temperatures T = 940, 980, 1020, 1060, 1100 °C. The time course of Fe and of steels oxidation is expressed by parabolic law l = kp . The surface oxidation is accompanied by decarburization of surface steel layers. The evaluation of measured carbon concentration profiles N(C,x,t) yields diffusion coefficients D(C,T). Oxidation coefficients kp(T) are linearly proportional to D(C,T).
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LONG-TIME OXIDATION OF .gamma.Fe AND LH15 STEEL AT HIGH TEMPERATURES IN AIR
Kučera, Jaroslav ; Adamaszek, K. ; Jurasz, Z.
The investigation of long-time oxidation of gFe and of low alloyed steel LH15 in ambient air is reported. The specimens of gFe had the form of wires with diameter f = 3.0 mm. The relative weight gain Dw/w of these specimens grows in the course of oxidation anneal due to the oxides FeO, Fe3O4, Fe2O3 formation. The weight gain is stopped at very long time period t of oxidation anneals. This phenomenon is denoted as saturation effect. The same effect was observed in the case of oxidation of specimens made from low alloyed steel LH15. The specimens had the form of cylinders with diameter .fi. = 10 mm.
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