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Simulated element redistributions in Ni-based superalloys weldments
Brož, P. ; Buršík, Jiří ; Sopoušek, J. ; Picha, R.
The diffusion and phase precipitation processes in welded joints of pure Al-Cr-Ni system and low alloyed Al-Cr-Ni-X systems (where X means Co, W, or Ti) were simulated using CALPHAD method and DICTRA software. The equilibrium calculations allowed to predict phase diagram cross-sections for the Al-Cr-Ni-X systems. The performed simulations based on local equilibrium condition in diffusion couple enabled to describe the phase transformation process and obtain redistribution of alloying species, activity profiles, and other time-distance dependences for other relevant values in diffusion-affected zone of the Al-Cr-Ni / Al-Cr-Ni-X weldments.
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Diffusion of galium in polycrystalline Ni3Ga
Mareček, P. ; Fous, T. ; Čermák, Jiří
The diffusion of 67Ga radiotracer in polycrystals of Ni3Ga intermetallic was studied by residual activity method. Both volume- and grain boundary diffusivity was investigated and quantitatively described. Obtained diffusivites of Ga in Ni3Ga lattice show the increasing dependence on increasing Ga concentration.
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Diffusion in Ni3Al-Co intermetallic
Gazda, A. ; Čermák, Jiří
Interdiffusion in Ni3Al intermetallic alloyed by 0-19 at %Co was studied in the temperature range 900-1200 C. An attempt was made, to analyze the interdiffusion coefficient into intrinsic diffusivities of individual components.Since no detecatble shift of inert markers was observed, it was concluded that the intrinsic diffusivities of Ni,Al and Co are aproximately equivalent one to another. The interdiffusion in pseudobinary alloys Al/Ni runs slightly faster than that in pseudobinary alloys Ni/Co. Measurements of 63Ni radiotracer in Ni3Al-Co was measured at 1000-1200 C by residual activity method. Enhanced Ni volume diffusivites observed at 1200C are most likely due to short-circuit diffusion along interphase boundaries in beta + gamma with comma field. The grain boundary diffusion of 63Ni was estimated at 1000C and 1100C. It was in a good agreement with our previous measurements made with pure Ni3Al.
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Grain boundaries in Ni3Ga as paths of rapid diffusion
Čermák, Jiří ; Růžičková, Jana ; Konecny, M. ; Ipser, H.
Grain boundary diffusivity P (P is a triple product of diffusion coefficient in grain boundary D, grain boundary width .delta. and segregation coefficient s) of nickel was measured by serial sectioning and residual activity methods in temperature interval 973-1373 K. Measurements are compared with our previous results on Ni grain boundary diffusivity in Ni3Al. It was obtained that the values of P for nickel in Ni3Ga are slightly higher than those for nickel in Ni3Al. The observed relation between Ps was interpreted by different affinity of diffusing Ni to different components X in the two Ni3X alloys.
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Teoretické studium difúze iontů dúležitých pro analýzu dechu metodou SIFT-MS
Dryahina, K. ; Španěl, Patrik
Accuracy of quantitative Selected Ion Flow Tube Mass Spectrometry SIFT-MS is ultimately determined by the proper accounting in the data analysis for the effect of differential diffusion. Diffusion loss of the product ions can be typically lower by a factor of up to 3 in comparison with the precursor ions. Hard sphere model of diffusion of polyatomic ions in helium has been used to calculate diffusion coefficients of the precursor and product ions involved in SIFT-MS quantification of common breath metabolites ammonia, acetone, isoprene, acetaldehyde and ethanol. Calculation involves semiempirical PM3 method for determination of the geometries of the ions, numerical averaging of the geometrical cross section for collisions with helium atoms and construction of a model interaction (12, 4) model potential followed by the analytical calculation of ionic mobility using momentum-transfer collision integral. Finally the values of diffusion enhancement factors have been calculated.
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Určení transportních charakteristik z protiproudé difuze plynů
Soukup, Karel ; Šolcová, Olga ; Schneider, Petr
Two types of a diffusion cell commonly used for studying of isobaric counter-current diffusion in porous solids are compared. Both cells enable determination of diffusion coefficients and transport characteristics of porous materials. Transport parameters are material constants of the porous solids and can be evaluated through application of a suitable model of porous solids to results of measurements of transport processes withing the porous structure
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