Lattice and Grain Boundary Self-Diffusion in Nickel

Abstract

Lattice and grain boundary self-diffusion coefficients of radioactive nickel 63 into high purity nickel have been measured over the temperature range 650°–475°C. The lattice diffusion coefficients, measured by radioactive counting of the surface, are given by DL=1.9 exp(−66 800/RT) cm2sec−1in agreement with previous measurements at higher temperatures. The grain boundary diffusion coefficients, determined from activity-penetration data, are similarly given by DB=0.07 exp(−27 400/RT) cm2sec−1and found to be independent of grain diameter in the range of about 0.03 to 0.07 mm.

Evidence for superplasticity in a CoCrFeNiMn high-entropy alloy processed by high-pressure torsion

“…In the present experiments, the activation energy of Q  113 kJ.mol -1 is much lower than the value of ~213 kJ mol -1 for the coarse-grained alloy below 1073 K [9] but nevertheless the value is in excellent agreement with the activation energy of ~115 kJ mol -1 reported for grain boundary diffusion in pure Ni [31]. This suggests that, as in conventional superplasticity [32], the rate of flow is controlled by grain boundary diffusion.…”

“…6 which shows, using logarithmic scales, the flow stress, , plotted against the initial strain rate, , for a superplastic material having different values for the grain size, d. At high strain rates the results for all samples with different grain sizes fall on a single line because flow occurs by an intragranular dislocation process which is independent of grain size where this corresponds to region III in conventional superplastic alloys. But in the superplastic regime, corresponding to region II, the behavior depends on grain size such that the smallest grain size exhibits the fastest strain rate for any selected stress because in superplasticity the strain rate varies inversely with grain size raised to a power of 2 [31].…”

Grain coarsening behaviour of solution annealed Alloy 625 between 600–800 °C

“…As a result, rather than a high activation energy transitional region as indicated in Figure 6, a discontinuous transition between the high and low velocity regions is most likely [46,37]. However, due to the narrowness of the inflection region, conclusive discrimination With regard to the specific vales detailed in Table 3 for Alloy 625, the activation energy for volume self-diffusion in Alloy 625 calculated as a weighted average from binary couples 170 detailed in the literature [47,48,49,50] is estimated as 148.6 kJ mol −1 . Accordingly, as the activation energy for grain boundary diffusion in nickel is typically around half that in the bulk [49] it is likely gain boundary diffusion which is the principle (i.e.…”

“…However, due to the narrowness of the inflection region, conclusive discrimination With regard to the specific vales detailed in Table 3 for Alloy 625, the activation energy for volume self-diffusion in Alloy 625 calculated as a weighted average from binary couples 170 detailed in the literature [47,48,49,50] is estimated as 148.6 kJ mol −1 . Accordingly, as the activation energy for grain boundary diffusion in nickel is typically around half that in the bulk [49] it is likely gain boundary diffusion which is the principle (i.e. subject to the aforementioned influence of solute drag and, separately, grain boundary/ interface diffusion) governing mechanism for grain growth over both the upper and lower temperature is subject to change with the gathering of more experimental data.…”

Sintering Mechanism of Two Spheres Forming a Homogeneous Solid Solubility Neck [Translated]^†

“…As mentioned above, since the authors' simulation method is based on the consecutive calculation operation at intervals of ∆t, it is possible to estimate the sintering behavior for the entire sintering process including the heating period, isothermal period, and cooling-off period that match the test conditions. The constants (Ashby, 1974;Wazzan, 1965) and conditions used for the simulation are listed in Table 2. …”