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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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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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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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