Metallographic Study of the Casting Made from CMSX-6 SC Nickel-Based Superalloy

Abstract

Microstructural characterization is an important tool to optimize the properties of engineering materials. Quantitative metallography is a common technique, which provides three-dimensional estimations of phases and structure elements from two-dimensional images. Metallography has been described as both a science and an art [1]. Superalloys are high-performance alloys which exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Temperature and corrosion resistant materials such as nickel-based superalloys are prepared mostly with standard metallographic techniques. However, the results can be significantly improved by using finely graded CMP (chemical mechanical polish) polishing solutions on a high napped polishing pad. Sample preparation requires a certain degree of skills and experience, due to the high chemical resistance of most superalloys. Some chemical solutions are able to dissolve the γ matrix and recover the γ' residue, and some others solutions can be used to obtain a contrary effect-dissolve the γ' phase precipitates and recover the γ matrix residue. The aim of the presented research is to describe qualitatively and quantitatively the as-cast microstructure of CMSX-6 SC superalloy. The author's attention has been concentrated on the γ' phase precipitates morphology. The results of using optical and scanning electron microscopy (SEM) are presented.