Seawater corrosion behavior of laser surface modified Inconel 625 alloy

Seawater corrosion behavior of laser surface processed Inconel 625 alloy was investigated. Three laser surface modified samples were prepared, one by laser melting, and the other two by laser melt/particle injection processing with tungsten carbide (WC) and titanium carbide (TiC) particles, respectively. Particle injection involved embedding the carbide particles into a laser melted surface and resulted in a metal matrix-particulate composite surface layer which was both hard and wear-resistant. While Inconel 625 is a corrosion resistant alloy suitable for marine applications, and WC and TiC are generally inert to chemical attack, results from this study showed that laser surface modification produced microstructures that were susceptible to seawater corrosion to varying degrees. Nominal corrosion was observed in the dendritic structure produced by laser melting of the alloy surface. In the particle injected samples, the WC particulate phase in contact with the Inconel alloy matrix showed different kinds of attack, while the TiC particulate phase showed none. In both particle injected samples, resolidification of the Inconel alloy melt produced significant departures in composition and microstructure from those of the base alloy. Eutectic and dendritic carbides and, in WC, interphase carbides were some of the resolidification byproducts that formed in the matrix surrounding the particulate. Alloyed with solute elements from the base alloy, each product phase contributed to unique forms of corrosion. A qualitative analysis of the corrosion behavior of the injected samples showed that corrosive damage was more severe in the WC injected sample than in the TiC injected sample and in the laser melted sample. This paper describes the processing, microstructural and compositional characterization, and seawater corrosion behavior of the laser surface modified samples, and attempts to explain the observations as a consequence of the formation of galvanic cells.