Characterization of Sacrificial Protection Efficacy and Longevity of a Thermal Spray Non-skid Coating under Sealants and Topcoats

摘要

Thermal spray non-skid (TSN) coatings are multifunctional coatings typically used on Navy flight decks to withstand extreme temperatures, provide a non-skid surface profile and serve as a barrier coating to the mild steel substrate. When the corrosion barrier coating is breached, TSN must provide sacrificial corrosion protection to the substrate. TSN coatings can have a high porosity and can be susceptible to micro-cracking under certain loading conditions (i.e., flight deck buckling). As a result, there is a motivation to apply sealants to increase the barrier protection capability and extend the service life of TSN. The desire to have both an effective barrier coating to protect the thermal spray while maintaining sacrificial protection of the substrate requires an intricate synergy between these methods of protection. An effective barrier coating aims to minimize exposed surface area and, when damaged, to prevent damaged areas from spreading over time. Conversely, a sacrificial layer requires a large exposed surface area proximate to the damaged area in order to maintain long term protection of the substrate. The objective of this work is to investigate this synergy in order to elucidate the factors that have the greatest influence over the corrosion protection properties and failure modes of TSN. Corrosion protection properties of TSN were determined as a function of cathodic protection efficacy and how sealants might reduce effective anodic surface area on both near and long term time scales. To evaluate these factors TSN coating were initially evaluated to determine the surface area of as-applied TSN coatings. The coatings were subjected to controlled anodic discharge cycles to determine characteristic changes in behavior. Coating degradation was characterized using a combination of impedance spectroscopy and electron microscopy to quantify protection strength and loss of available active surface area as a function of different coatings and simulated exposure conditions (i.e., salt spray, extreme temperature, etc.).