Crystallographic aspects of intergranular failure of archaeological silver artefacts

Abstract

Excavated archaeological silver objects often exhibit extended intergranular degradation. This failure is most probably caused by the localised corrosion of highly copper-segregated grain boundaries in case of a Ag-Cu base alloy during burial for more than 1000 years in graves. Detailed electron backscatter diffraction (EBSD) analysis of individual grain boundaries showed that this corrosion degradation is controlled by the crystallography of the grain boundaries: exclusively, the general grain boundaries are prone to the corrosion while the special ones are not attacked at all. It is also deduced that the orientation of the grain boundary plane plays an important role in the selective corrosion attack. © 2010 John Wiley & Sons, Ltd.