Effect of radiation exposure on the structure and diffusion in the near-surface layer of ultrafine-grained nickel

The effect of irradiation with a pulsed electron beam (PEB) in the mode of surface melting absence on the copper diffusion in the near-surface layer of ultrafine-grained (UFG) nickel has been studied. The profiles of the copper concentration distribution over depth after isothermal diffusion annealing and annealing under PEB irradiation of the UFG nickel surface are determined. It has been established that as a result of PEB irradiation, the coefficient of grain-boundary diffusion of copper in nickel increases and the mode of grain-boundary heterodiffusion changes in the near-surface layer of nickel in comparison with isothermal diffusion annealing.

Constraints on non-isothermal diffusion modeling: An experimental analysis and error assessment using halogen diffusion in melts

Diffusion chronometry on zoned crystals allows constraining duration of magmatic evolution and storage of crystals once temperatures are precisely known. However, non-isothermal diffusion is common in natural samples, and thus timescales may not be determined with confidence while assuming isothermal conditions. The “non-isothermal diffusion incremental step (NIDIS) model” (Petrone et al. 2016) is proposed for such cases for a non-isothermal diffusive analysis. We conducted diffusion experiments with stepwise temperature changes to analyze and test the model, evaluated the associated errors and improved the accuracy by suggesting an alternative algorithm to model diffusion times. We used Cl and F (≤0.4 wt%) as the diffusing elements in nominally anhydrous (H2O ≤ 0.3 wt%) phonolitic melt with composition of Montana Blanca (Tenerife, Spain) in an experimental setup that successively generates multiple diffusive interfaces for different temperatures by adding glass blocks of different Cl and F concentrations. This compound set of two diffusion interfaces represents distinct compositional zones that diffusively interact at different temperatures, which can be taken as an equivalent to non-isothermal diffusion in zoned magmatic crystals. The starting temperature ranged from 975 to 1150 °C, and each set of experiments included a temperature change of 85–150 °C and a total duration of 8–12 h. The experiments were carried out in an internally heated pressure vessel equipped with a rapid quench device at 1 kbar pressure. Cl and F concentration profiles were obtained from the quenched samples by electron microprobe analysis. Although the estimated diffusion times from the NIDIS-model matched well with true experimental values, the errors on estimated timescales, due to errors in curve-fitting and uncertainty in temperature, were ±10–62% (1σ). The errors are much larger at 61–288% (1σ) when the uncertainty in diffusivity parameters is included. We discuss the efficiency and limitations of the model, assess the contribution from different sources of error, and their extent of propagation. A simpler alternative algorithm is proposed that reduces errors on the estimates of diffusion time to 10–32% (1σ) and 60–75% (1σ), with and without including uncertainty in diffusivity parameters, respectively. Using this new algorithm, we recalculated the individual diffusion times for the clinopyroxene crystals analyzed by Petrone et al. (2016) and obtained a significantly reduced error of 26–40% compared to the original error of 61–100%. We also analyzed a sanidine megacryst from Taapaca volcano (N. Chile) as a test case for non-isothermal modeling and obtained diffusion times of 1.5–9.4 ky, which is significantly different from isothermal analyses including a previous study on similar sample. In this analysis, the error estimated by our new method is reduced by 63–70%.

Isothermal Diffusion Behavior and Surface Performance of Cu/Ni Coating on TC4 Alloy

The poor surface performance of titanium alloys substantially limits their application in many fields, such as the petrochemical industry. To overcome this weakness, the Cu and Ni double layers were deposited on the surface of TC4 alloy by the electroplating method, and the isothermal diffusion process was performed at 700 °C to enhance the binding ability between Cu and Ni layers. The isothermal diffusion behavior and microstructure of the coating were systematically analyzed, and tribological property and corrosion resistance of the coating were also evaluated to reveal the influence of isothermal diffusion on the surface performance. It was shown that multiple diffusion layers appeared on the Cu/Ni and Ni/Ti interface, and that NixTiy and CuxTiy phases were formed in the coating with the increase of diffusion time. More importantly, Kirkendall diffusion occurred when the diffusion time increased, which led to the formation of continuous microvoids and cracks in the diffusion layer, weakening the surface performance of the Cu/Ni coatings. This paper unveils the relationship between the microstructure of the Cu/Ni coatings and isothermal diffusion behavior, providing guidelines in preparing high performance surface coatings.

Влияние угла наклона канала на конвективное смешение, вызванное неустойчивостью механического равновесия тройной газовой смеси при изотермической диффузии

The features of the convective regime that arose due to the instability of mechanical equilibrium of the ternary helium – argon – nitrogen gas mixture during isothermal diffusion were experimentally studied. The influence of the slope angle of the diffusion channel on the intensity of convective flows is considered. The intensity of partial transfer of components in the inclined channel at elevated pressures was measured. A nonlinear dependence of the mixing rate of the components on the angle of inclination was found. It has been established that the observed transfer of components, which is atypical for diffusion, is possible with a certain composition of the gas mixture.