Insights into Galvanic Corrosion Behavior of Ti Cu Dissimilar Joint: Effect of Microstructure and Volta Potential
The effect of microstructure on corrosion behavior of a solid state explosion welded Ti Cu bimetal is investigated by means of alternating current direct current (AC DC) electrochemical measurements, optical microscopy, scanning electron microscopy, and scanning Kelvin probe force microscopy (SKPFM) The results indicate that the titanium regions in the welding interface, local melted zone (LMZ) and LMZ Cu interface are potential sites for initiation of corrosion attacks. SKPFM mapping clearly shows that before exposure of the sample to a 3.5% NaCl corrosive solution and at the beginning of the exposure, the Cu side of the bimetal has a higher Volta potential in comparison to that of the Ti region, and thus acts as a cathode. Electrochemical measurements also confirm that titanium acts as an anode and copper as a cathode, in the first moments of immersion, in accordance with macroscopic observations and SKPFM results. However, by growing a passive layer of titanium oxide and titanium hydroxide on the Ti side after about 1 h exposure to the corrosive medium, the titanium side becomes nobler and the polarity arrangement in the galvanic couple reverses.
Materials