Laser fabrication of W-reinforced Cu layers: I. Corrosion behavior in 3.5% NaCl solution and synthetic acid rain

• Laser-fabricated layers contain micron-sized W particles in a Cu matrix.
• They have lower Icorr than that of cp Cu despite the active shift in OCP.
• Preferential dissolution of Cu binder occurs and W particles are finally detached.
• Micro-galvanic effect of both phases plays an important role in corrosion behavior.

Surface modification of commercially pure copper (cp Cu) with W powder was achieved by using a high power diode laser (HPDL) resulting in a microstructure of micron-sized W particles in a Cu matrix. In both 3.5 wt% NaCl solution and synthetic acid rain (SAR), the laser-fabricated specimens possess lower corrosion current density (Icorr) than that of cp Cu despite the active shift in open-circuit potential (OCP). Although Cu is cathodic to W in 3.5 wt% NaCl solution, the Cu phase in the laser-fabricated specimens dominantly dissolves during the immersion test. This anomalous observation is possible because the OCP values of the laser-fabricated specimens, cp Cu and cp W are quite near to each other, while the anodic and cathodic current densities are all not negligible for the Cu and W phases at OCP. As the anodic current density of the Cu phase is greater than anodic current density of the W phase, the Cu phase corrodes more quickly than the W phase. For the laser-fabricated specimens immersed in SAR, the Cu phase is anodic and is selectively attacked while the W phase is passive due to the formation of WO3.