The Impact of Material Choice on Galvanic Incompatibilities

OEMs deliver military aircraft with carefully chosen materials and coatings in order to minimize the impact of corrosion. However, when exposed to corrosive environments the protective systems degrade, and even initially perfect protective systems become damaged. The problem becomes more complex as we add new materials such as carbon fiber composites and metal-filled polymers into the mix of airframe materials. Matters  are further exacerbated by environmental regulations that are driving OEMs and customers toward alternative coatings and treatments in place of Cd, Cr, etc that can have very different galvanic consequences (e.g. replacing Cd with ZnNi or electroless Ni-PTFE). The wide spectrum of material properties can lead to severe galvanic corrosion resulting in safety risks, costly repair and reduced time-on-wing.

The challenge for the operator is significant, especially with new materials and coatings – it is essential to maximize the operational availability, so when faced with a degraded protection system it is necessary to repair it as quickly as possible, without the unintended consequences that can occur in a complex system.

In this paper we show how a new physics-based corrosion prediction software tool currently being developed and tested for use in the ‘design office’ is already proving to be a useful diagnostics tool in MRO (Maintenance Repair Overhaul), helping to explain how the corrosion event occurred, and what can be done to prevent it happening again. The simulation tool enables materials and process engineers to assess the impact of proposed material and coating choices – moving from a find and fix approach to a more sensible predict and manage.

This paper shows how this modeling approach can be used in design and overhaul to make better material choices and quantify the severity of corrosion that can occur when materials are changed or damaged in various aircraft systems.