Corrosion behaviour and microstructural study of TiZnNi laser deposited on titanium alloy

The corrosion behavior of TiZnNi/Titanium composite via Direct Laser Metal Deposition (DLMD) process was investigated. From the results, changes in shift of the corrosion potentials of the coatings were shown through linear polarization curves. The corrosion potentials were compared to that of base metal (Ti-6Al-4V alloy). The corrosion potentials of the coatings were slightly higher than the control. This is due to the noble characteristics of the coatings. Some phases such as NiTi, TiO and Ni4Ti3 forme during laser deposition process could have contributed to the resistance of the coating to corrosion. These phases are nobler therefore base metal would be attacked first by corrosion. Polarization resistance showed increase in values in comparison to the base metal. These protective oxides in form of titanium oxide are very steady, reliable and stick to the surface of the specimen against corrosion. They prevent further attack from corrosion reaction. Asides titanium oxides, aluminium and vanadium oxides also act as protective oxides. The surroundings determine the characteristics and structure of protective oxides. Likewise, the surroundings also determine the rate of surface degradation. The mitigation of protective oxides against the surroundings is what brought about the passivation. This occurs but cutting off access of hostile ions from the surroundings onto the matrix of the metal.