Investigation of the reasons for the destruction of cast brass lighting devices dated to the end of the 19th and the beginning of the 20th century

The article is devoted to the study of the causes of the destruction of cast brass lighting fixtures of the late 19th – early 20th century during their restoration. The aim of the study was to study how casting defects, as well as composition and microstructure, affect the tendency to fracture of these products. To solve the problem, a collection of fragments of cast brass fittings of lighting devices of the time under consideration was selected from the funds of the State Research Institute for Restoration. Their composition was determined using X-ray fluorescence analysis on a HitachiX-Met-8000 instrument, and microstructural features on a MIM-8 metallographic microscope. The elemental composition of the inclusions was recorded using a HitachiTM4000Plus scanning electron microscope equipped with Quaniax 75 (Bruker) microrentgenospectral analysis. It was found that the fragments were cast from brass containing from 19.6 to 34% zinc and from 1.44 to 3.27% lead, as well as tenths of a percent impurities of sulfur, chlorine, silicon, aluminum, and calcium. The microstructure of the fragments was characterized by large cast crystallites with pronounced dendritic liquation, the impurities formed brittle intermetallic compounds with zinc and lead, they stood out along the boundaries of the cast crystallites and in the dendritic spaces, and pores were concentrated there. These defects reduced the strength and ductility of the fragments. As a result, the products could be destroyed during restoration in case of mechanical impact.