Vacancy loss at grain boundaries in quenched polycrystalline gold

Abstract

Vacancy loss at a variety of grain boundaries in 99.999 wt.% pure polycrystalline gold quenched from 930°C and aged at 60°C was studied by transmission electron microscopy. The vacancy precipitate (stacking-fault tetrahedra) free zones, which formed in the regions adjacent to grain boundaries due to vacancy loss at these sinks during quenching, were analyzed. The vacancy sink efficiency of both small-angle and non-special large-angle grain boundaries was found to be high in the presence of the large chemical potential of the quenched-in vacancies. While there is some evidence that the sink efficiency at small angles is somewhat smaller than at large angles, the results are not inconsistent with a constant vacancy sink efficiency for all of the small-angle and non-special large-angle boundaries observed. On the other hand, the sink efficiency of the special Σ = 3 coherent twin boundary is significantly lower than for the non-special boundaries. The results are discussed relative to other work in the field, and it is concluded that: (1) both small-angle and non-special large-angle boundaries operate as highly effective sinks at high vacancy chemical potentials; (2) the sink efficiency tends to fall off as the chemical potential decreases or the boundary becomes more special, i.e., more ordered.