SEAWATER CORROSION BEHAVIOR OF LASER-SURFACE MODIFIED INCONEL-625 ALLOY

Seawater corrosion behavior of laser surface processed Inconel 625 all oy was investigated. Three laser surface modified samples were prepare d, one by laser melting, and the other two by laser melt;particle inje ction processing with tungsten carbide (WC) and titanium carbide (TiC) particles, respectively. Particle injection involved embedding the ca rbide particles into a laser melted surface and resulted in a metal ma trix-particulate composite surface layer which was both hard and wear- resistant. While Inconel 625 is a corrosion resistant alloy suitable f or marine applications, and WC and TiC are generally inert to chemical attack, results from this study showed that laser surface modificatio n produced microstructures that were susceptible to seawater corrosion to varying degrees. Nominal corrosion was observed in the dendritic s tructure produced by laser melting of the alloy surface. In the partic le injected samples, the WC particulate phase in contact with the Inco nel alloy matrix showed different kinds of attack, while the TiC parti culate phase showed none. In both particle injected samples, resolidif ication of the Inconel alloy melt produced significant departures in c omposition and microstructure from those of the base alloy. Eutectic a nd 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 p roduct phase contributed to unique forms of corrosion. A qualitative a nalysis 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 descri bes the processing, microstructural and compositional characterization , and seawater corrosion behavior of the laser surface modified sample s, and attempts to explain the observations as a consequence of the fo rmation of galvanic cells.