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Control of intergranular oxidation by thermal treatment
Rothová, Věra ; Buršík, Jiří ; Svoboda, Milan
The effect of pre-annealing at 800 °C in argon atmosphere on high temperature corrosion at 1050 °C in air was studied on two high purity nickel grades and compared to a commercial purity nickel. Moreover, the influence of fabrication was analyzed in the case of cast and cold-rolled Puratronic® nickel samples. The mutual grain orientation was measured by means of electron backscatter diffraction and grain boundaries were characterized in terms of the coincidence site lattice model. The scanning electron microscope characterization of cross sections of all the oxidized samples has been performed and compared with the literature. The influence of purity and fabrication on the high temperature oxygen ingress in nickel was discussed in terms of grain boundary character distribution.
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The effect of annealing conditions on grain growth an microstructure in nickel
Rothová, Věra ; Svoboda, Milan ; Buršík, Jiří
In this paper, the influence of processing conditions (annealing atmosphere and temperature) on grain growth and microstructure evolution in nickel of two purity grades (99.5% and 99.9945%) was investigated. As regards pure nickel, the kinetic and thermodynamic parameters describing grain growth and the resulting evolution of twins during annealing in argon at 600–1100 °C has been studied and compared with the literature data. By the help of cross-sections of commercial purity nickel after annealing in air and/or argon, the effect of environment on grain growth was explained in relation to the depth of internal oxidation zone.
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Influence of lattice defects on grain boundary self-diffusion in nickel
Rothová, Věra ; Buršík, Jiří ; Svoboda, Milan
An extremely wide spectrum of experimental results on the grain boundary (GB) self-diffusivities in nickel was published in the literature. Currently, our previously published results show a pronounced dependence of diffusivities on both purity and thermo-mechanical history. A possible reason for the large scatter of published experimental data could be a contribution arising from some crystal lattice defects other than GBs. Thus, in the present work, the impact of the selected lattice defects on diffusion processes, grain growth and twin production has been investigated. Hence, the cast and cold-rolled nickel specimens of purity grades from 99.5% to over 99.99% were selected to study the influence of the material purity and fabrication on microstructure and its evolution during thermal treatment and thereby on the mass transport properties.
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