Reexamination of grain-boundary sliding by diffusion

Steady-state sliding of grain boundaries is discussed by taking into account the change in the potential energy of an applied stress, when the sliding occurs by diffusional accommodation. The present analysis enables us to derive the sliding rates at boundaries of various shapes in a simple manner without knowing local stress fields. Sliding rate of a boundary containing second phase particles is also derived by similar calculations. The results are compared with previous calculations by other investigators, and it is found that the resultant expressions for the sliding rates are essentially identical to those derived from more complex analyses.     

Chemical stresses induced by grain-boundary diffusion

Based on Whipple-Suzuoka solutions, the chemical stresses induced by grain-boundary diffusion under constant- and instantaneous-source concentrations are investigated. For a finite boundary, the chemical stress consists of both compression and tension fields, in the sequence of compression I-tension-compression II, with the compression I field near the diffusion interface. The magnitudes and distributions of these fields differ for different source concentrations and are strongly affected by the ratio of diffusivity in the grain boundary and diffusivity in the lattice (D′/D). As D′/D increases, the magnitude of the compression I field decreases and that of the tension and compression II fields increases. An increase in D′/D also increases the range of the compression I field. The trend is distinct in the case of constant-source diffusion, while in the case of instantaneous source diffusion, both the tension and compression II fields appear to be extremely small.     

Densification by interface-reaction controlled grain-boundary diffusion

The densification of a fine-grained, high-purity aluminum oxide powder under hot isostatic pressing (HIP) has been found to occur by interface-reaction controlled grain-boundary diffusion. We discuss geometries and dislocation mechanics for this process for both the initial and final stages of densification and develop constitutive equations for densification rate as a function of density, materials constants, and experimental parameters. The model is used to explain the results of several HIP experiments at pressures of 34–102 MPa and temperatures of 1273–1423 K. Sources of variation from sample to sample are discussed. An analysis is made of the sensitivity of the model to its adjustable parameters. Alternative explanations for the experimental data are discussed and found to be inadequate.     

Creep cavity growth under interaction between lattice diffusion and grain-boundary diffusion

A model and a method of numerical analysis of the cavity growth in grain boundaries in metals due to lattice diffusion are proposed. The growth behavior simulated is compared to that due to grain-boundary (GB) diffusion. The simulation method is extended to analyze the growth under the interaction between lattice diffusion and GB diffusion. The growth rate calculated under the interaction is approximately equal to the linear sum of those due to the pure lattice diffusion and the pure GB diffusion.     

Role of grain-boundary diffusion in the grain growth in nanocrystalline nickel

The grain growth in a nanocrystalline nickel during nonisothermal annealing is studied by differential scanning calorimetry (DSC) and transmission electron microscopy. Nanocrystalline nickel is prepared by electrodeposition at a pulsed voltage. Its nonisothermal annealing is accompanied by anomalous grain growth; at a temperature corresponding to a DSC peak, a bimodal grain structure forms. The processing of DSC signals in terms of the Avrami formalism permits the grain growth activation energy to be determined, which is found to be close to the activation energy of grain-boundary self-diffusion. The anomalous grain growth creates conditions such that grain-boundary diffusion is a controlling stage of the process.     

Relations between the parameters of grain-boundary diffusion of zinc in aluminum

Experimental results on the grain-boundary diffusion of zinc in aluminum bicrystals containing 〈100〉 and 〈111〉 tilt boundaries at normal and high hydrostatic pressures have been considered. A comparison of the diffusion activation energies and the activation volumes for grain boundaries having the same crystallographic parameters has revealed a linear relation between these kinetic constants. The diffusion activation energy is found to increase with the activation volume. This relation is shown to correspond to the compensation effect well-known in diffusion theory.     

脱氧铜中磷的测定

本文建立了脱氧铜中磷的分析方法：在稀H2S04介质中,单独用SnCl^2还原磷钼黄为磷钼蓝,此法的最大吸收波长为680nm,磷含量在1．0-50μg／25ml范围内符合比尔定律。研究了十几种可能存在的共存离子对磷的影响,并将此法用于铜合金标样和脱氧铜中磷的测定,结果满意。     

Lattice and grain boundary diffusion of cerium and neodymium in nickel

Diffusion of cerium and neodymium in nickel has been studied by the serial sectioning technique using radioactive tracers¹⁴¹Ce and¹⁴⁷Nd, in the temperature ranges 700° to 1100°C for volume and 500° to 875°C for grain boundary diffusion respectively. Volume diffusivities can be expressed as: $$\begin{gathered} D_{Ce/Ni} = (0.66 \pm 0.18)\exp \left( { - \frac{{60,800 \pm 810}}{{RT}}} \right)cm^2 /\sec \hfill \\ D_{Nd/Ni} = (0.44 \pm 0.13)\exp \left( { - \frac{{59,820 \pm 830}}{{RT}}} \right)cm^2 /\sec \hfill \\ \end{gathered} $$ and grain boundary diffusivities by: $$\begin{gathered} Dg_{Ce/Ni} = 0.11\exp \left( { - \frac{{29,550}}{{RT}}} \right)cm^2 /\sec \hfill \\ Dg_{Nd/Ni} = 0.07\exp \left( { - \frac{{28,580}}{{RT}}} \right)cm^2 /\sec \hfill \\ \end{gathered} $$ Results of volume diffusion have been compared with those calculated from the theories of diffusion based on size and charge difference between the solute and the solvent atoms. Whipple and Suzuoka methods have been used to evaluate the grain boundary diffusion coefficients. Both the methods give similar results.     

磷锑钼杂多酸-孔雀绿-聚乙烯醇体系分光光度法测定压延磷铜板中微量磷

在硫酸介质中,钼酸铵和酒石酸锑钾与磷形成的杂多酸阴离子再与孔雀绿形成离子缔合物,在聚乙烯醇的作用下,测定磷的灵敏度明显提高,据此提出了在水相中测定压延磷铜板中微量磷的分光光度法。探讨了显色剂、表面活性剂、缓冲溶液的用量以及显色时间等对吸光度的影响,着重考察了不同的表面活性剂对体系的增溶增敏作用。实验测得离子缔合物的最大吸收波长为650 nm,表观摩尔吸光系数为1.52×105L mol-1.cm-1,磷含量在0~0.40μg/mL内符合比尔定律。样品中大量铜的干扰采用硼氢化钾还原沉积,使基体中大量铜与微量     

Grain-boundary diffusion of germanium in copper and Cu-Ge and Cu-Fe alloys

The grain-boundary diffusion (GBD) of germanium in copper and its alloys Cu-2% Ge and Cu-0.5% Fe is investigated in the temperature range of 500?C590°C by means of electron-probe microanalysis. The GBD parameters (triple product P = s??D _GB and effective activation energy E) are found. The temperature dependence of the triple product for germanium GBD in pure copper can be described by equation P = 3 × 10¹⁵exp[?80 kJ mol^?1/(RT)] m³ s^?1. It is shown that the addition of Ge has almost no effect on the GBD parameters in copper, while doping with iron leads to a considerable reduction in the triple product.     

Synergetic effect of hardness and phosphorus grain-boundary segregation on the ductile-to-brittle transition temperature of 17-4 PH steel

The influence of hardness and phosphorus grain-boundary segregation (PGBS) on the ductile-to-brittle transition temperature (DBTT) of a 17-4 PH martensitic steel was studied. Thermal treatments including long-time aging at low temperature were made to get different hardness levels and different PGBS amounts. A synergetic effect between PGBS and hardness on the DBTT of the steel is evidenced; in other words, the DBTT shift due to PGBS increases with hardness. If hardness is low enough, PGBS can even have no effect on the DBTT. A tentative interpretation of this synergetic effect is proposed, based on the assumption that the detrimental effect of PGBS on the grain-boundary cohesion increases with temperature.     

Coarsening of grain-boundary precipitates

The coarsening behavior of grain-boundary precipitates is theoretically investigated. After an initial period of instability a pseudostationary distribution of particle sizes is approached. Then the average particle size increases with the fourth root of time. The distribution function shows a cut off at 1.33 times the average size.     

Measurement and representation of grain-boundary texture

The measurement and representation of grain-boundary texture in single-phase polycrystals are examined in this article. Grain-boundary texture is assumed to be fully defined by the lattice orientation of two grains which come together to form the boundary and by the orientation of the boundary relative to the two lattices. Representations which incorporate more limited def- initions of local grain-boundary structure are easily considered in natural subspaces of the more complete representation. The two major stereologies which have been developed for measuring grain-boundary texture from random sectioning are compared in detail. It is demonstrated that the stereological method of Hilliard, [3] which obtains the distribution of boundary normals from intersections of the boundaries with random test lines placed on random sections, cannot dis- tinguish “sided” grain-boundary textures. The stereological method of Adams, [5] which obtains the boundary normal distribution from the angular distribution of boundary intersections in ran- dom sections, is shown to be more general, since it is not limited to “nonsided” grain-boundary textures. It is also shown that the latter stereology obtains a more accurate representation of the boundary-normal distribution, as compared with the former, for an equivalent number of section planes. Formerly Graduate Student, Yale University.