G. Meyrick

On the initiation of discontinuous precipitation

Abstract It is proposed that a general criterion for distinguishing between alloys in which discontinuous precipitation can occur and those in which it does not, is the degree to which the solute elements tend to segregate at grain boundaries. By considering the tendency for a boundary segment to bulge it has been demonstrated that for CuSb alloys the criterion is fulfilled and that the general trends in other alloys are consistent with it. The necessary information is presently unavailable for more quantitative tests.

A new technique for measuring the effects of oxygen activity on surface energies: Application to nickel

A new technique for oxygen fugacity control was used in conjunction with the microcreep method for determination of surface energy. Oxygen fugacity was controlled by electro-statically controlled pumping through a solid zirconia electrolyte. The method was applied to the measurement of the surface energy of nickel at 1300°C as a function of oxygen fugacity in the range 10-6 to 10-13 N/m2. The determined surface energy value, 2.12 J/m2, at the lowest oxygen fugacity is in good agreement with other measurements, while values at other pressures indicate a variation with oxygen adsorption similar to that observed for copper. Twin and grain boundary energies were also determined and found to agree well with earlier work once a texture effect for metal foils was included in the analysis.

Anomalously fast diffusion in the Fe-Zn System

The rate of diffusion of Zn into Fe in solid Fe/Zn diffusion couples is found to be two to four orders of magnitude greater than would be predicted by lattice diffusion. The penetration depth varies markedly from sample to sample. It is achieved primarily in an initial transient, and then stops even though a steep concentration gradient persists in the ferrite. The maximum concentration of Zn in the ferrite surface layer often exceeds the published solubility of the first intermetallic phase, gamma, in ferrite. The initial Zn penetration seems to occur by DIGM. The mechanism for continued penetration is less clear. The variability in percent Zn in the ferrite, and possibly the variation in penetration depth, must stem from the delay in the nucleation of the most iron rich intermetallic phase, gamma.

Surface relief produced by diffusion induced boundary migration in Cu-Zn

Experimental observations are presented that demonstrate that diffusion induced grain boundary migration in copper foils exposed to zinc vapor, from a Cu-15 pct Zn alloy, can be studied directly after treatment without etching. The general characteristics of migration are in accord with previous investigations, but novel changes in the surface topography are described. Pits were formed on the surface of areas swept by boundary migration; also, the surface was often converted into a series of corrugations. The formation of pits suggests that the grain boundary diffusivity of zinc exceeds that of copper. The corrugations are believed to indicate that boundaries sometimes move in an intermittent manner.

Microstructural characterization of novel in-situ Al-Be composites

The microstructure of cast and extruded in-situ Al-Be alloys, of compositions of Be-37Al-3Ni (wt pct) and Be-34Al-2Ni-2Ag-2Si (wt pct), was investigated using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The study indicates that both the Be and Al phases are continuous. The Be phase has a coarse dendritic structure in the as-cast material. Fractographic analysis of failed tensile specimens tested at room temperature revealed basal-plane cleavage failure of the Be phase and ductile failure of the Al phase. A significant number of deformation twins were observed in the Be phase when the tensile loading axis was parallel to the Be dendrite growth axis. An additional fracture mode was observed in the samples tested at elevated temperatures. At elevated temperatures, decohesion of the Al-Be interface was observed on the fracture surface. This phenomena was observed to increase as the test temperature increased from 150 °C to 315 °C. A high density of dislocations with a tangled morphology were observed in the Al phase after the tensile test. These were determined to be associated with easy slip of 1/2〈101〉-type dislocations. The limited ductility of the Be phase was attributed to the predominant basal slip of 〈a〉-type dislocations, b = 1/3〈1120〉, and the lack of dislocations with 〈c〉 components. However, a significant number of dislocations with 〈c〉 components were found in localized areas of the Be phase after extrusion.

On the dislocation density in aluminum during Harper-Dorn creep

Abstract In research on high temperature, low stress, creep in aluminum, Lacombe and Beaujards etchant has been used to determine dislocation densities. This work has led to the suggestions that the density is about 108 m−2 or less and independent of stress and that for Harper-Dorn creep the density must be below a critical value of about 2×109 m−2. Here, the characteristics of the etchant have been reviewed and it has been shown that they are complex and that pit densities are generally unreliable measures of dislocation populations. The purpose of this note is to point this out and to suggest that further work on dislocation populations during Harper-Dorn creep is warranted.

Formation of supersaturated FeZn alloys by DIR

On decrit la formation de nouveaux grains riches en Zn sur la surface du fer dans des couples de diffusion fer-zinc

Capacitance–torsion balance for measuring small stresses and strains

A versatile and inexpensive capacitance-torsion balance has been developed to measure, simultaneously and continuously, small forces and displacements in remotely located samples. It can also be used as a sensitive dilatometer or as a microbalance. The present instrument provides an output voltage change of 1 V for a load change of 3 g and a displacement of 5x10(-5) m. These load and displacement ranges can be independently chosen by adjusting the geometrical configuration of the balance, whereas the sensitivity is independent of the range.