Electrochemical corrosion behavior of CoCrFeNiMo-Ni bonded (Ti,W)C-based cermets with added nano-TiN in NaOH solution

In this work, CoCrFeNiMo-Ni bonded (Ti,W)C-based cermets with varying nano-TiN incorporations were fabricated through vacuum sintering, and their corrosion behavior in 1mol/L NaOH solution was systematically explored via electrochemical corrosion testing, including open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopy. The corrosion mechanism was further characterized on the basis of the morphology and composition characterization of corrosion products. Unlike the conventional cermets using Ni/Co as the whole binder, the CoCrFeNiMo-Ni bonded cermets presented significantly enhanced corrosion resistance in NaOH solution. This enhancement was highly correlated with the generation of passive products on the cermet surface, predominantly composed of TiO 2 , Cr 2 O 3 , Cr(OH) 3 , Fe(OH) 3 , Fe 2 O3, Fe 3 O4, Co 3 O 4 , Co(OH) 2 , NiO and Ni(OH) 2 , which effectively inhibited further corrosion. Upon varying the nano-TiN content within the range of 0 - 2.5 wt.%, the corrosion resistance was significantly enhanced. The corrosion potential exhibited a positive shift from -0.248 V to -0.216 V (vs Hg/HgO), accompanied by a diminishment in corrosion current densities from 4.859 μA/cm 2 to 1.619 μA/cm 2 , with a decrease of about 67%. This was mainly attributed to the increased TiO 2 , Cr 2 O 3 , and Cr(OH) 3 content in corrosion products, reduced ceramic particle size and enhanced creased density of cermets. However, excessive incorporation of nano-TiN induced the porosity and the formation of more M 6 C phases, which eventually weakened the corrosion resistance.