Corrosion Performance of Laser Posttreated Cold Sprayed Titanium Coatings

The recent development of cold spray technology has made possible the deposition of highly reactive, oxygen sensitive materials, such as titanium, without significant chemical reaction of the powder, modification of particle microstructure and with minimal heating of the substrate. However, the presence of interconnected pathways (microscale porosity) within the deposit limits the performance of the metallic coating as an effective barrier to corrosion and substrate attack by corrosive media is usually inevitable. The aim of the present study was to investigate the effects of processing, including a postspray laser treatment, on the deposit microstructure and corrosion behavior. Commercially pure titanium (CP Ti) was deposited onto a carbon steel substrate, using a commercial cold spray system (CGTTM Kinetiks® 4000) with preheated nitrogen as both the main process gas and the powder carrier gas. Selected coatings were given a surface melting treatment using a commercial 2 kW CO2 laser (505 Trumpf DMD). The effect of postdeposition laser treatment on corrosion behavior was analyzed in terms of pore structure evolution and microstructural changes. Optical microscopy, scanning electron microscopy, and x-ray diffraction were employed to examine the microstructural characteristics of the coatings. Their corrosion performance was investigated using electrochemical methods in 3.5 wt.% NaCl (ASTM G5-94 (2004)). As-sprayed titanium coatings could not provide favorable protection to the carbon steel substrate in the aerated NaCl solution, whereas the coatings with laser-treated surfaces provided barrier-like properties.