Abstract

Acid treatment of grey cast iron sample 2 (GJS 400) yielded fragile graphite-like lamellae containing abundant spherical diamond inclusions and Diamond-Like Carbon (DLC). Microscopic observations showed that the approximately 10-30μm thick lamellae contain diamonds about 2.5μm in diameter distributed throughout their volume, including below the surface. Raman measurements identified diamond-related bands, although overlapping signals from graphite, DLC, nanodiamond, and diamond broadened the spectra, as did laser-induced carbon degradation. The lamellae’s transparency and depth-dependent optical appearance indicate they are not pure graphite but include a substantial DLC component. The observations suggest a complex carbon structure formed under locally elevated pressure, possibly near the graphite-diamond equilibrium. The formation conditions and precise thermal history remain uncertain, but the findings indicate that conventional grey cast iron phase diagrams may not describe all stages of cooling.

Keywords: Grey cast iron; Diamond inclusions; Diamond-like carbon; Graphite lamellae; Raman spectroscopy; Nanodiamond; Carbon phases; High pressure; Boron phases; Phase diagrams