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.

Metallurgical investigation on fourth century BCE silver jewellery of two hoards from Samaria

“…Hence, numerous studies of ancient silver artefacts exist in the literature, investigating their chemical composition15161718192021, microstructure1517202223, manufacturing processes1524, provenance1617, embrittlement and fracture2223, condition of preservation, corrosion processes and corrosion products142526272829 and their state of conservation2529. These studies normally combine non-destructive testing (NDT) and destructive testing methods, including: metallography, light and scanning electron microscope (SEM) examination including energy-dispersive spectroscopy (EDS) analysis, focused ion beam (FIB) microscopy and micromachining, particle-induced X-ray emission (PIXE) analysis, X-ray fluorescence (XRF) analysis, inductively-coupled plasma (ICP) analysis, X-ray diffraction (XRD), neutron tomography, X-ray photoelectron spectroscopy analysis (XPS), and Raman spectroscopy analysis1516171819202122232526272829303132. Yet, because of the rareness of such ancient artefacts, from the archaeological perspective, the use of NDT methods is always preferred202130.…”