Jiří Čermák

Short-circuit diffusion in NiAl alloys

Abstract The tracer grain boundary diffusivity, P, of nickel in polycrystalline NiB, Ni-9 at%AlB and in NiAlB intermetallic has been measured with boron concentrations xB up to 0.3 at% B. The measurements were done by the residual activity method in the temperature interval from 773 to 1073 K. It was observed that P decreases with growing concentration of boron in NiB and Ni-9 at% AlB. This behaviour is similar to the dependence of P on xB in Ni3Al, reported in our previous paper. In boron-doped NiAl intermetallic, on the other hand, P does not depend on xB.

Ni and Ga diffusion in polycrystalline Ni3Ga

Abstract The volume and grain boundary (GB) diffusion of 63Ni and 67Ga radiotracers in polycrystals of Ni3Ga intermetallic was studied in the vicinity of the stoichiometric composition A3B (23.5–28.3 at.% Ga). Both volume and GB diffusivity was investigated in the temperature interval 773–1373 K by the residual activity method. The obtained Ga volume diffusivity increases with increasing Ga concentration xGa; the increasing tendency of Ni volume diffusivity with increasing xGa is pronounced at lower temperatures. GB diffusivity of both Ga and Ni in Ni3Ga are close one to another and—contrary to the diffusion behavior of components in Ni3Al—they do not show any significant dependence on xGa.

Grain-boundary diffusion of chromium in Ni3Al intermetallic modified by Fe, Cr and Zr

Abstract Tracer grain-boundary diffusion (GBD) of chromium Cr-51 in slightly hypostoichiometric ( x Al 3 Al alloys containing several at. pct of Fe, Cr and Zr was studied using both serial sectioning and residual activity methods. Measurements of the product of the diffusion coefficient in grain boundary and the width of grain boundary, P , were carried out in the temperature interval from 773 to 1273 K. It was found that the addition of Fe and Cr up to about 6 at% does not alter the diffusion characteristics of Cr grain-boundary diffusion. The addition of a small amount of Zr, on the other hand, tends to increase the activation enthalpy and pre-exponential factor of Cr grain-boundary diffusion.

Effect of Nickel Purity on Self-Diffusion along High-Diffusivity Paths

In the temperature range 600–1000 °C, the effect of material purity on self-diffusion along grain boundaries has been studied in both the pure (Puratronic 99.9945%) and the technical (99.5%) nickel. The penetration profiles were measured by the serial sectioning method using the 63Ni radiotracer. The extensive electron backscatter diffraction (EBSD) analysis was performed on the same samples in order to reveal possible differences in microstructure induced by the impurity content. The obtained microstructure characteristics were further interpreted in terms of the coincidence site lattice (CSL) model.

Investigations of grain boundaries in copper using emission Mössbauer spectroscopy

Grain boundaries (GBs) in pure Cu specimens were studied by means of 57Fe emission Mössbauer spectroscopy. A spectrum component which can be ascribed to iron atoms at GBs is represented by the single line with isomer shift 0.67 ± 0.05 mm/s. It is interpreted as iron atoms at GB sites with expanded atomic volumes and highly symmetric distribution of surrounding atoms.

Grain-boundary diffusion of nickel in Cr-, Fe-, and Zr-modified Ni3Al intermetallic

Abstract Tracer grain-boundary diffusion of 63 Ni in slightly hypostoichiometric ( x Al 3 Al alloys containing several percents of Cr, Fe and Zr was studied using both serial sectioning and residual activity methods. Measurements of grain-boundary diffusivity P were carried out in the temperature interval 873–1273 K. It was found that the additions of Cr, Fe and Zr decrease the P and increase the activation enthalpy of 63 Ni grain-boundary diffusion.

Volume heterodiffusion of tungsten in Fe-Cr ferritic alloys

Abstract Tracer diffusion of 181 W in Fe — 8–12 %Cr alloys was measured by serial sectioning method. It was obtained that the variation of Cr concentration in the range from 8 to 12 wt. % or additions of carbon up to 0.17 wt.%, or low alloying with other elements (see Tab.1) has not any significant effect on tungsten volume heterodifusion coefficient. The temperature dependence of obtained volume diffusion coefficients of tungsten shows the magnetic diffusion anomaly. It was fitted by semiempiric Eq.(2) proposed by Jonsson that can be taken as a convenient interpolation formula for rapid calculations of W diffusivities in 8–12 %Cr ferritic steels in engineering practice.

Diffusion of 65Zn in the Mg17Al12 intermetallic compound and in the Mg-33.4wt.% Al eutectic

Abstract The coefficient of 65Zn heterodiffusion in the Mg17Al12 intermetallic compound (-phase) and the eutectic alloy Mg-33.4wt.% Al was measured in the temperature region 598–698K using serial sectioning and residual activity methods. The diffusion coefficient of65Zn in the intermetallic can be written as DI=1.5×10−2m2s−1× exp(–154.3kJmol−1/RT). At temperatures T648K, where the mean diffusion path is greater than the mean interlamellar distance in the eutectic, the effective diffusion coefficient Deff=2.710−2m2s−1exp(–155.1kJmol−1/RT) was evaluated. At two lower temperatures, the diffusion coefficients 65Zn in interphase boundaries were estimated: Db (623K)=1.610−12m2s−1 and Db (598K)=4.4 10−13m2s−1. The specific (Mg)/ interfacial energy =140mJm−2 was assessed from measurement of the time dependence of interlamellar distance during isothermal anneal.

Zn Diffusion in Binary Base of Light Mg-Al Alloys

Heterodiffusion of 65Zn in Mg, Mg – x Al (x = 1.77, 3.9 and 9 wt.% Al) and in the commercial AZ91 alloy was studied in the temperature interval 498 – 848 K by serial sectioning and residual activity methods. The concentration and temperature dependence of Zn bulk diffusion coefficient D is described by the relation D = exp (0.1 × cAl – 9.16) × exp (-125.8 kJ mol-1/RT) m2 s-1 (cAl – concentration of Al in wt.%). Zn grain boundary diffusivity P = s δ Db (s – segregation factor, δ - grain boundary width and Db – diffusion coefficient in grain boundary) was also determined and it was found that it obeys the Arrhenius law P = 7.2 × 10-15 × exp (-46 kJ mol-1/RT) m3 s-1.

Grain Boundary Self-Diffusion in Nickel

Grain boundary self-diffusion in both the cast and the cold-rolled Puratronic 4N5 nickel was studied in the temperature range from 600 °C to 1000 °C. The experiments were carried out with the samples pre-annealed at 1100 °C in comparison to the samples pre-annealed at intended individual diffusion temperatures. The relative grain orientation was analyzed on the same samples by means of electron backscatter diffraction (EBSD) and grain boundaries (GBs) were characterized in terms of the coincidence site lattice (CSL) model. Considering the non-linear Arrhenius temperature dependencies obtained for most specimens by using conventional method of profile evaluation in the B-type kinetics and the appearance of two high-diffusivity paths in diffusion profiles measured, a more suitable BB-type and AB-type diffusion models were applied for data evaluation.