Physics and phenomenology of strain hardening: the FCC case

The present paper reviews experimental results for the magnitude of the stacking fault energy (γ) in pure fcc metals, and its variation with alloying and with temperature. Quantitative studies have principally involved electron microscopic observations of faulted defects (extended nodes, extrinsic-intrinsic fault pairs, tetrahedra) or the determination of rolling textures, while much valuable information has also been obtained from measurements of the X-ray faulting probability. Extensive measurements of the variation of γ with alloying have been made in silver, copper, and nickel base alloys and in stainless steels, from which general conclusions can be drawn regarding the composition dependence of γ with various solute types. The presence of irregular faulted configurations in samples of some high solute concentration alloys following room temperature deformation suggests that solute/dislocation pinning forces can exert considerable influence on the dislocation substructure. Annealing such samples leads to a reduction in the degree of irregularity of the substructure and generally to a decrease in mean faulted defect size. These changes appear to be due to the reduction, through a thermally activated process, of the effectiveness of the solute pinning forces rather than as a result of a strong dependence of γ on temperature. The variation of faulted defect size on annealing pure materials is likely to arise solely from the variation with temperature of γ and the elastic constants, and results in silver indicate that γ/G is approximately independent of temperature.

The influence of alloying, temperature, and related effects on the stacking fault energy

Using standard imaging techniques of electron microscopy it is not possible to resolve the partial dislocations having the equilibrium separation for dissociated dislocations in the pure face-centred cubic metals. Consequently the stacking-fault energy γ cannot be determined from direct measurements of the separations of the partials. In this paper it is demonstrated that such determinations are possible using the weak-beam method of electron microscopy. The separations of Shockley partial dislocations in silver and copper have been measured, as a function of dislocation line orientation, using this method. From these measurements, the values γsilver= 16·3+1·7 erg cm−2 and γcopper= 41±9 erg cm−2 have been obtained from analyses based on anisotropic elasticity theory.

The measurement of stacking-fault energies of pure face-centred cubic metals

The stacking-fault energies of a number of copper alloys with electron-atom ratios less than or equal to 1·10 have been measured from observations of single dissociated dislocations imaged...

On the stacking-fault energies of copper alloys

Stacking‐fault energies can be determined by measuring the positions and profiles of x‐ray diffraction lines. Use of this method has been hampered by the uncertainty of the relationship between stacking‐fault energy and the ratio of microstrain to stacking‐fault probability. Microstrains and stacking‐fault probabilities have been determined for five fcc metals by x‐ray diffraction line profile analysis. For these metals, Ag, Au, Cu, Al, and Ni, stacking‐fault energies have been estimated from a comprehensive updated review of the experimental literature. A linear correlation does exist between γ and 〈e502〉111/α and thus, the x‐ray technique can be applied more confidently. The possible role of elastic anisotropy is also considered.

P.G.J Gallagher

Papers

The diversity of stacking fault energy determinations and its significance