Initial Yielding in Gold–Indium Alloys

Abstract

The yielding behaviour of polycrystalline gold-indium alloys is very dependent on the solute concentration and the deformation temperature. At low and intermediate temperatures (− 196 to 200° C (77 to 473 K)) yield inflections are observed that in the 2 and 4% indium alloys increase in size with decreasing temperature, in contrast to the 6 and 8% indium alloys, in which the inflections decrease and in the case of the 8% indium alloy die out at − 196° C (77 K). The different behaviours can be understood in terms of a temperature-dependent dislocation-unlocking mechanism combined with a temperature-dependent or independent work-hardening rate after yielding. At between 200 and 400° C (473 and 673 K) a smooth transition between elastic and plastic flow takes place. At high temperatures pronounced yield points are observed. The more concentrated alloys display yield points at lower temperatures, e.g. the 8% indium alloy exhibits the effect at 400° C (673 K), while the 2% indium alloy shows no yield point even at 590° C (863 K). The onset of the yield points corresponds to the high-temperature drop-off in yield stress. An estimate of 1·4–1·8 eV is obtained for the activation energy of the high-temperature yielding process. A deformation mechanism controlled by the dragging of solute atmospheres can explain the effect.