Evaluation of Various Etching Solutions for Microstructural Characterization of Inconel 792 Superalloy

Abstract

Metallography is one of the most effective techniques for microstructural characterization of metals and alloys. The present study examined the microstructure, morphology, and distribution of the principal precipitated phases in Inconel 792 superalloy. To achieve precise microstructural analysis, several etching solutions were applied: acetic acid (CH3COOH), nitric acid (HNO3), hydrochloric acid (HCl), Marble’s reagent, and sulfuric acid (H2SO4, employed as a surface activator. Optical microscopy images showed that the as-cast Inconel 792 exhibits a dendritic grain structure with no preferred orientation. Carbides, γ′ precipitates, and γ/γ′ eutectic regions were clearly visible in these micrographs. Phase identification was corroborated by complementary techniques, including X-ray diffraction (XRD), uniaxial tensile testing, and scanning electron microscopy (SEM). Etchants based on acetic acid (CH3COOH), nitric acid (HNO3), and hydrochloric acid (HCl) effectively revealed the precipitated phases. Marble’s reagent proved particularly suitable for delineating the dendritic structure.