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Kombinovaný difúzní režim nízkorozpustné příměsi v polykrystalu – Modelový systém – Ge v Mg a ve slitině Mg-1,8 wt.% Al
Čermák, Jiří
Unusual diffusion regime observed in a case of extremely low-soluble element in Mg alloys was described. The low solubility of diffusant was found to affect significantly the transport properties in the range, where the volume diffusion usually operates. The proposed way of data evaluation enabled calculation of segregation factor of Ge in Mg and in alloy Mg – 1.8 wt. % Al. Temperature dependence of measured diffusion coefficient in grain boundary, Db, grain boundary diffusivity, P, and temperature dependence of calculated segregation factor, s, obey the Arrhenius relation.
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Diffusion of C and Mn in steel weldment Fe-0,3C/Fe-0,3C-15Mn
Král, L. ; Million, Bořivoj ; Čermák, Jiří
In the present paper, the results of measurements of C and Mn diffusion in steel weldments of ternary alloys Fe-0.3C/Fe-0.3C-15Mn are reported. Alloys were cast in induction furnace under protective Ar atmosphere. Ingots were hot-forged to rods of the diameter 15mm and homogenized. After annealing they were machined on diameter 12mm and cut into pieces of 4mm thickness. These cylindrical samples were ground and welded by electrical impulse. Diffusion couples were sealed into evacuated silica ampoules together with Ti-chips. They were annealed at 500-1100 °C for 1.5-96 hours. Measurement of carbon and manganese redistribution was done by means line segment microanalysis in normal direction to welded interface using electron scanning microscope Philips SEM-505WDS equiped with Microspec WDX-2A. Diffusion coefficients of C and Mn were obtained and the relations between them were found.
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A new method of estimation of diffusion characteristics in ternary systems
Čermák, Jiří ; Rothová, Věra ; Gazda, Aleš
A method was proposed based on an estimation of components of diffusion matrix, Dij, in ternary systems. It makes possible to obtain the concentration dependence of DijŽs in a wide range of concentrations using one diffusion couple only. It is in contrast to the conventional procedure that needs two diffusion couples and provides DijŽs for a single composition related to an intersection of diffusion paths. The method was applied to gammaŽ one-phase interdiffusion in Ni3Al-X (X = Cr, Fe, Nb, Ti) in temperature interval 1173 ů 1533 K.
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In-situ monitoring of phase transformation in Ni3Al based alloys by means of hydrogen permeation measurement
Rothová, Věra ; Čermák, Jiří
Nickel aluminide Ni3Al crystallizes in the cubic L12 structure (Cu3Au type). It is known from the literature that this structure remains unchanged up to the melting point. However, under certain circumstances, it can change from L12 to other non-cubic ordered crystal structures. There have been reported some data which indicate that the presence of hydrogen may facilitate the change in the structure. Present detailed study of hydrogen permeation behavior in both the Ni3Al and the CMSX-4 has shown very sensitive changes of permeation rate depending upon temperature variations.
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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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