Influence of Welding Operational Conditions on Partial Mixed Zone Formation in Ni-Based Dissimilar Weld Overlay

Nickel based alloys are a special class of materials for engineering with excellent corrosion resistance for harsh environments and are used in various industries. Among several types of applications, its use like coatings is very interesting due to a significant cost reduction. However, microstructural changes in interface can produce heterogeneous regions along fusion boundaries. The incomplete mixing between Ni-based alloy and steel can produce heterogeneous Fe-rich regions near fusion boundary with additions of alloying elements like Ni, Cr, Mo. The local chemical composition results in a high hardenability and martensite formation. These partial mixed zones (PMZ) with martensite can damage the coating bond. The main objective of the present work was to evaluate some operational conditions on martensite partial mixed zones formation in fusion boundary of nickel-based alloys weld overlays deposited by the GTAW cold wire feed on C-Mn steel plates. The Taguchi method was applied. The control factors investigated were the type of nickel-based alloys, type of shielding gas, heat input level, type of arc oscillation and The microstructure was investigated using light microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive of X-ray spectroscopy (EDS), backscattering electron diffraction (EBSD). Coating bond and microhardness tests were carried out to evaluate some mechanical properties. The results showed that the global dilution level of weld overlay does not have any influence on PMZ content. However the interface coating/substrate were influenced by the operational conditions, and the formation of PMZ with martensite was mainly influenced by the heat input level, shielding gas and arc oscillation, which are strongly related to amount of metal deposited per unit length and melted pool agitation.