Microstructural evolution and improved corrosion resistance of NiCrSiFeB coatings prepared by laser cladding

Abstract

Abstract Inconel 625 (IN 625) is widespread in the manufacturing of critical components such as nuclear reactors, control rods, steam turbines, supercritical boilers, rotary shafts, aerospace engines, etc., that operate in severe harsh environments. However, if the service environments consist of sulphur (fuel tanks), chlorine (supercritical boilers and heavy water plants), H2S, HCl, etc., this alloy will suffer from localized corrosion attacks that minimize its resistance towards corrosion, followed by sudden failure. This study is aimed to facilitate the anti-corrosion characteristics of IN 625 by cladding it with Colmonoy 5 (NiCrSiFeB) alloy particles. The clad microstructure was revealed by micrographs captured by means of optical and field emission scanning electron microscopy followed by the nanoindentation study to analyze the hardness offered. Corrosion testing was carried out on both IN 625 and Colmonoy 5 clad samples at various intervals (0, 13, 27 and 56 h) for interrogating the corrosion behavior in terms of Tafel and impedance plots along with the surface roughness examination using scanning probe microscopy. The results showed that the clad region consists of dendritic microstructure along with the segregation of interdendritic Cr-rich precipitates after solidification. These interdendritic precipitates aid in improving the hardness at the clad region. Moreover, the clad samples have better anti-corrosion characteristics because of the existence of dendritic and interdendritic phases compared to the IN 625 samples in terms of current density, polarization resistance and average surface roughness values.