Intrinsic Stacking Fault Energy Research Articles

Stacking fault energy determinations in hcp silver-tin alloys

Measurements of the intrinsic stacking fault energy as a function of tin solute concentration are reported throughout the range of the intermediate hexagonal ζ-phase. Four different alloy compositions from 12 to 17 at. % tin were studied. Extended dislocation nodes and dislocation double ribbons were observed and measured. The stacking fault energy values obtained from measurements on these two configurations were in good agreement and indicated that the magnitude of the stacking fault energy increased linearly with solute concentration in the hcp phase. These results are compared with those from cubic α-phase Ag-Sn alloys previously reported. The dislocation configurations in the hexagonal alloys are briefly described.

Studies of the Effect of Annealing on Extended Dislocation Nodes in Silver‐Tin Alloys

AbstractExtended dislocation nodes have been observed by transmission electron microscopy and measured in several solid solution silver‐tin alloys after annealing at elevated temperatures. The intrinsic stacking fault energies were determined and compared with previously reported values for freshly deformed specimens. Only small irreversible changes in the fault energy were found after annealing up to 600°C, in contrast to results found in some other alloy systems. The effect of oxygen on the node extensions in pure silver was also studied.

Studies on Extended Dislocation Nodes in a ζ-Phase Silver-Tin Alloy

A determination of the intrinsic stacking fault energy as a function of composition has been previously reported for the face-centered-cubic phase in the silver-tin alloy system. The method involved direct measurements on extended dislocation nodes observed by transmission electron microscopy in alloys containing from 0 to 7.8 at.% tin. The stacking fault energy γ was found to decrease from a value of 22.8 erg/cm3 for silver to 4.2 erg/cm2 for the 7.8 at.%. alloy. Figure 1 shows the phase diagram for this system. At room temperature, the α-phase limit occurs at about 8.5 to 9 at.%. tin. A two-phase region extends to approximately 11.5 at.% followed by the ζ- Ag Sn phase region which exists to about 17 at.% tin. A series of hexagonal ζ alloys of various compositions are presently under study to determine the variation of the stacking fault energy with composition. Preliminary results indicate that the stacking fault energy increases with increasing solute concentration in the ζ-phase region. Extended dislocation nodes have been observed in all the ζ alloys, together with extended ribbons in the dilute alloys. This paper will consider only the results obtained on the most dilute alloy (12 at.% tin) and compare them with the a-phase results.

The influence of a dilute magnesium addition on the growth ant shrinkage of dislocation loops in aluminium

Abstract The influence of a dilute magnesium addition to pure aluminium on the climb of dislocation loops has been studied by isothermal annealing of thin foils of Al-0·65% Mg. Faulted loops were observed to shrink at temperatures above 130°C, whereas prismatic loops above a critical size grew at temperature? ≳200°C; in pure aluminium they generally shrink. The various mechanisms previously proposed to account for excess vacancies have been critically examined and shown to be inconsistent with the experimental observations, and an alternative mechanism based on the growth of a surface oxide is proposed. Experimental observations consistent with the oxide growth mechanism are described. The variation of shrinkage rate with temperature for both prismatic and faulted loops over a wide temperature range has been determined. The results, which do not conform to emission controlled kinetics, have been analysed in terms of diffusion controlled behaviour to deduce an accurate value for the intrinsic stacking-fault energy of Al-0·65% Mg. Comparison of the annealing rate of faulted loops in the alloy and pure aluminium indicates that the Mg atom-vacancy binding energy is extremely small.

Dislocation node determinations of the stacking fault energy in silver-tin alloys

Direct measurements by transmission electron microscopy on extended dislocation nodes in alloys of tin in silver have led to values for the intrinsic stacking fault energy. The values decreased smoothly from 23 ergs/cm 2 for pure silver to 4.5 ergs/cm 2 for 7.8 at.% tin, near the f.c.c. phase limit. The results are compared with previous determinations in other silver-base alloys, and sources of systematic error are discussed. A comparison of different theoretical analyses is included.

THE STACKING-FAULT ENERGY IN α-SILVER – TIN ALLOYS

Direct measurements by transmission electron microscopy on extended dislocation nodes in alloys of tin in silver have led to values for the intrinsic stacking-fault energy. The values decreased smoothly from 23 erg/cm2 for pure silver to 4.2 erg/cm2 for 7.8 at.% tin. The results are compared with previous determinations in other silver-base alloys.

Estimate of Extrinsic Stacking-Fault Energies from Dislocation Configurations

In this paper we use straight-line models of observed extrinsic nodes to estimate extrinsic stacking-fault energies. Using isotropic elasticity theory and neglecting interactions, we find simple expressions for the energy in terms of the inscribed radii of the nodes. We apply the results to observed extended nodes in a silver—8 at.% tin alloy and find a ratio of extrinsic to intrinsic stacking-fault energy of about 3.

The stacking-fault energy in the Ag-In series

Abstract The intrinsic stacking-fault energy has been determined in the Ag-In series using extended nodes, from pure silver to Ag-12.5 wt. % In (e/a = 1.23). The present results show that the stacking-fault energy is insensitive to alloying up to e/a ≁ 1.04, after which it decreases with increasing solute content. Extrinsic faulting has been observed throughout the alloy series including pure silver and in all cases the extrinsic and intrinsic stackingfault energies are approximately equal. Following high temperature annealing treatments, the effective stacking-fault energy in high solute content alloys is observed to increase irreversibly, suggesting the presence of a solute impedance force at room temperature.

An Absolute Determination of the Extrinsic and Intrinsic Stacking Fault Energies in AgIn Alloys

AbstractObservations have been made of extrinsic‐intrinsic node pairs, and of a hitherto unreported fault pair. It is shown that a simple estimate of the ratio of extrinsic to intrinsic stacking fault energy (γe/γi) cannot be made from the inscribed radii of node pairs, and that earlier qualitative results that γe/γi > 2, or more, are invalid. The simple geometry of the new fault pair facilitates a straight forward absolute determination of both γe and γi. Contrary to published results, γe and γi have been found to be approximately equal. For the present alloys, γe/γi = 1.09 ± 0.1 (for the electron —atom ratio e/a = 1.15) and γe/γi = 1.03 ± 0.1 (for e/a = 1.23). Good absolute agreement has been obtained between γi determined from the fault pairs, and from the observation of extended three‐fold nodes. It is concluded that extrinsic faults are rarely observed because of a high impedance to their formation arising from the co‐operative glide which is necessary, but that, once formed, the extrinsic fault energy is closely the same as the intrinsic.

The nature of faulted defects in low stacking-fault energy alloys

Abstract Examination, by transmission electron microscopy, of a deformed Ni 70 at. % Co alloy has shown that, although all glide faults examined were intrinsic, extended extrinsic nodes and intrinsic-extrinsic stacking-fault bends occur. However, none of the stacking-fault tetrahedra formed during deformation was found to be extrinsic. From these results it is deduced that the extrinsic stacking-fault energy is considerably greater than the intrinsic stacking-fault energy, and it is suggested that the shape of the extrinsic nodes may be determined by the high value of the extrinsic stacking-fault energy.