Leveraging Finite Element Method Modeling to Evaluate ZnNi Plating as a Mitigation Strategy for Galvanically Induced Environmental-Assisted Cracking of a P675-Anodized Titanium Multicomponent Assembly

A combined experimental and computational approach was performed to assess the environmental-assisted cracking (EAC) risk of Pyrowear 675 coupled to anodized titanium in a multicomponent assembly exposed to 0.6 M NaCl. The ability of a sacrificial ZnNi layer (plated from an alkaline bath) to mitigate the cracking risk through control of the galvanic couple potential on the assembly was assessed. Experimental analyses of the electrochemical kinetics and (any inherent variability) of anodized titanium, Pyrowear 675, and electroplated ZnNi are presented. Both anodic and cathodic kinetics generated on P675 showed significant variability for the measured open-circuit potential (OCP) charge transfer kinetics between the as-received and polished surfaces. The electroplated ZnNi was shown to have variability from batch to batch in its OCP (100 mV range) and rate of anodic dissolution in its as-received state. Dissolution of Zn during OCP exposures of the ZnNi led to ennoblement of the material upward of 300 mV to a final OCP measured as −575 mVSCE after 10 weeks of exposure. The experimentally generated kinetics were utilized for finite element method modeling predictions to assess the viability of ZnNi as a tool for the mitigation of the EAC risk in a complicated, multimetal assembly. Through probing the variability in the electrochemical kinetics of P675 and ZnNi, the amount and location of ZnNi applied to the assembly, the changes in potential from possible partial wetting scenarios, and the ennoblement of ZnNi, a fail-safe solution, was shown to be possible.