Grain Boundary Diffusion Of Ag Research Articles

Bulk and grain boundary diffusion of Ag in γ-FeNi alloy

Abstract Solute diffusion of Ag in polycrystalline γ-Fe-40 wt.% Ni alloy was studied by means of the radiotracer technique. For bulk and grain boundary diffusion, the following Arrhenius parameters were established: D v 0 = 1.2 × 10 − 3 m 2 / s $ D_v^0 = 1.2 \times {10^{ - 3}}{m^2}/s $ and Q v = 279 kJ/mol and P 0 = 8:1 ⨯ 10–14 m3/s and Q gb = 126 kJ/mol, respectively. The diffusion profiles reflect the very low Ag solid solubility which was estimated in the alloy via the specific activity of the applied 110mAg radiotracer.

Grain boundary diffusion of Ag through polycrystalline SiC in TRISO fuel particles

The effective diffusivity and release fraction of Ag in polycrystalline SiC are evaluated using a kinetic Monte Carlo model. The effects of various grain boundary network properties on the transport of Ag across the SiC layer have been examined, including fraction of grain boundary type, spread in grain boundary diffusivities and distribution of grain boundary types. It is shown that the effective diffusivity and release fraction of Ag can exhibit a large variability due to changes in the GB structure of SiC, and this variability is almost independent of temperature fluctuation. The present results suggest that the variation in properties of grain boundary networks in SiC may contribute to the spread in the Ag diffusivity and release fraction measured in TRISO particles. It is also found that the grain boundary diffusion alone may be insufficient to account for the Ag diffusivities and release fractions measured in integral release experiments. Additional factors such as irradiation and temperature distribution may also play an important role in Ag transport across the SiC layer.

Diffusion of Ag and Co in ultrafine-grained α-Ti deformed by equal channel angular pressing

Grain boundary diffusion of Co and Ag was investigated in coarse-grained and ultrafine-grained (UFG) α-Ti. Ultrafine grained Ti was produced by equal channel angular pressing (ECAP) and diffusion measurements were performed in a temperature interval where no significant grain growth occurred. Grain boundary diffusion of Co was found to be 1-2 orders of magnitude slower in UFG Ti, despite the attendant activation enthalpy being similar to that in coarse-grained α-Ti. By contrast, grain boundary diffusion of Ag occurred at a significantly higher rate in the ECAP-modified UFG Ti. This behaviour is associated with the specific diffusion mechanisms of Ag and Co: while Ag diffuses preferentially via substitutional sites, diffusion of Co is dominated by interstitial jumps. The existence of so-called non-equilibrium interfaces in UFG Ti, providing an increased density of traps for the interstitially diffusing Co and simultaneously enhancing substitutionally diffusion of Ag, is confirmed by the diffusion measurements.

Bulk and grain boundary diffusion of Ag in γ-FeNi alloy

Solute diffusion of Ag in polycrystalline γ-Fe-40 wt.% Ni alloy was studied by means of the radiotracer technique. For bulk and grain boundary diffusion, the following Arrhenius parameters were established: D 0 v = 1.2 × 10 -3 m 2 /s and Q v = 279 kJ/mol and P 0 = 8.1 × 10 -14 m 3 /s and Q gb = 126 kJ/mol, respectively. The diffusion profiles reflect the very low Ag solid solubility which was estimated in the alloy via the specific activity of the applied 110m Ag radiotracer.

Grain Boundary Diffusion and Linear and Non-Linear Segregation of Ag in Cu

Ag grain boundary (GB) diffusion was measured in the Cu-0.2at%Ag alloy in a wide temperature range from 473 to 970 K. The direct measurements of Ag GB diffusivity D alloy gb under conditions of the Harrison C regime revealed that D alloy gb is almost identical to D pure gb determined earlier for Ag diffusion in high-purity Cu (Divinski, Lohmann, and Herzig, 2001). The penetration profiles determined in the Harrison B regime showed a complex, multi-stage shape. This diffusion behavior can be rationalized assuming that besides GBs significantly covered by segregated Ag atoms, some fraction of GBs remains almost free from Ag atoms in the studied temperature interval. The total amount of “pure” GBs drastically decreases with decreasing temperature. This hypothesis was proven by measurements of Ag GB diffusion in Cu near Σ5 bicrystals, which allowed us to analyze in detail the non-linear segregation of Ag in Cu GBs.

Determination of grain-boundary diffusion of Ag in nanocrystalline Cu by the Hwang–Balluffi method

From the Ag and Cu Auger signals measured on the surface of nanocrystalline Cu/Ag thin bilayers, the temperature dependence of the parameter ω′ for Ag grain-boundary diffusion in Cu (ω′=δkbDb/δsks, where δ and δs are the width of the grain boundary and the segregated layer and kb and ks are the grain-boundary and surface segregation factors, respectively) have been determined by the Hwang–Balluffi method in the C-kinetics regime over the temperature range of 393–428 K. These values have been compared with triple products, P=δkbDb, determined in the temperature range 584–804 K by Bernardini et al. [Phil. Mag. A 73, 237 (1996)] using radio tracer technique in the B-kinetics regime and the temperature dependence of the surface segregation factor has been extracted. The surface segregation energy (34±16 kJ/mol) agrees well with other data published in the literature.

Structure of Ag/Co multilayers on excimer laser irradiation

The structure of Ag/Co multilayers (MLs) on laser irradiation is studied. Three MLs with different Ag layer thicknesses, denoted according to the nominal values (nm) as Ag2Co1, Ag4Co1, and Ag6Co1, were exposed to XeCl excimer laser pulses of the fluences (0.1–0.25) J cm −2 for (1–200) times. The structure was examined by X-ray diffraction, hard X-ray reflectivity, and diffuse scattering measurements at grazing incidence. The polycrystalline face-centered cubic structure of Ag layers with random orientation of the grains was found in as-deposited Ag2Co1 and Ag6Co1. The formation of a discontinuous ML by grain boundary diffusion of Ag into Co layers induced by laser treatment was evidenced in Ag6Co1 while the temperature window for diffusion is too narrow for completing such a process in Ag2Co1. The granular structure formed due to the melting of Ag layers has no direct relation to the original ML. A strong texture of Ag layers found in Ag4Co1 stabilizes the as-deposited structure even when the melting of Ag layers starts. Different structural evolution of three samples under study is responsible for their different behaviour of giant magneto resistance on laser irradiation observed previously.

Intermixing in immiscible Co/Ag/Co trilayers under XeCl laser annealing

Co/Ag/Co trilayers were studied in order to confirm our previous results on the laser irradiation improvement of GMR ratio in immiscible Ag/Co multilayers (MLs). E-beam deposited samples were processed by XeCl excimer laser at the fluenees F = 0.15, 0.2, 0.3 and 0.36 J/cm 2 with n = 1−100 pulses of 30 ns duration. The temperature versus time evolutions were computed for the first laser pulse. Samples were studied by grazing incidence XRD, RBS and resistometry. From results it follows that grain boundary diffusion of Ag across Co layers going through even during short irradiation times, may be the explanation of GMR improvement via transformation of continuous ML into discontinuous one.

Effect of segregation on the shape of grain boundary diffusion profiles Experimental study of the Cu[sbnd]Ag system

Abstract Grain boundary diffusion of Ag in Cu and in a Cu-0.091 at.% Ag alloy has been investigated. An experimental method to separate the effect of different grain boundaries present in the samples and the effect of segregation on grain boundary diffusion profiles is described. It is shown that in the case of silver diffusion in pure copper the curved penetration plots are due to segregation effects. For pure Cu the obtained activation energy and pre-exponential factor of the triple product P are (90 ± 6.2)kJ mol−1 and (3.7+7.3 −2.5) × 10−14 m3s−1, respectively. For Cu(Ag) alloy these values are (119.4 ± 6.6)kJ mol−1 and (2.1+4.8 −1.5) × 10−12m3s−1, respectively. The activation energy of grain boundary segregation is estimated as 37± 13kJmol−1.

Grain Boundary Diffusion in NiFe/Ag Bilayer Thin Films

ABSTRACTX-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Ag through 250 Å thick Ni80Fe20 (permalloy) films in the temperature range of 375 to 475°C. Grain boundary diffusivities were determined by modeling the accumulation of Ag on Ni80Fe20 surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Ag through Ni80Fe20 is characterized by a diffusion coefficient prefactor, D0,gb, of 0.9 cm2/sec and an activation energy, Ea,gb, of 2.2 eV. The Ni80Fe20 film microstructure has been investigated before and after annealing by atomic force microscopy and x-ray diffraction. The microstructure of Ni80Fe20 deposited on Ag underlayers remained relatively unchanged upon annealing.

Determination of the activation energy of Ag diffusion through grain boundaries of thin Au films by using AES in a simplified accumulation method

An analysis of the measurement of grain boundary diffusion of Ag through Au films of 100 nm thickness in the temperature range of 125–225°C by using a simplified accumulation method was performed. Auger electron spectroscopy (AES) was used for observation of Ag formation on the Au surface, due to Ag diffusion along grain boundaries of the thin Au film. The results of the measurements were compared with the results obtained previously by using different techniques and different experimental methods.

Grain-boundary diffusion of Ag through Cu films

The interdiffusion of bimetallic couples consisting of 1850 Å Cu/1550 Å Ag on sapphire substrates has been studied using Rutherford backscattering for anneal temperatures ranging from 225 to 500 °C. The Ag-Cu couple was chosen because it represents a system in which only grain-boundary diffusion as opposed to lattice diffusion should occur. No Ag-Cu intermetallic compounds have been reported and the equilibrium solid solubility of Ag in Cu and Cu in Ag is under 3 at.% for the temperature range of interest. A series of in situ isothermal vacuum anneals established the following mechanism for interdiffusion in these couples. Initially, the Cu grain boundaries saturate with Ag. Then Ag atoms in the Cu grain boundaries diffuse to the Cu surface and spread out. Finally, the diffusion process ceases when about one monolayer of Ag covers the Cu surface. Also, at temperatures exceeding 350 °C, grain growth at the Ag-Cu interface roughens that interface and makes Rutherford-backscattering analysis more difficult. Grain-boundary diffusivity has been calculated employing the model of Hwang and Balluffi. Agreement with published values obtained by radioactive-tracer measurements on foil samples is quite good. A discrepancy was observed between grain size of Cu as estimated by the saturated concentration of Ag in Cu grain boundaries and that determined by TEM measurements. This can be accounted for by assuming that some grain boundaries are blocked by light impurity atoms or that the grain-boundary segregation coefficient of Ag in Cu is not unity. In either case, it is shown that analysis of the Rutherford-backscattering spectra with the Hwang and Balluffi model can take account of these factors.