Surface Engineering Process for Lightweight Materials Used in Aerospace Applications

The European Space Agency awarded Captain Corrosion OÜ in 2024 with 125 000 € to develop coatings for lightweight materials used in aerospace applications.

In this project, we investigated the efficiency of coatings that were prepared by utilizing trivalent chromium based chemical conversion as pre-treatment and reinforcement with nanocoatings via sol-gel and atomic layer deposition (ALD). The pre-treatment was done with our new prototype Captain Corrosion Conversion Coating. A selection of ISO 9227 neutral salt spray test results from the project is depicted in Fig. 1.

Figure 1. Photos taken after 168h ISO 9227 neutral salt spray test of AA 2024-T3 substrates that had no coating (a), the Captain Corrosion Conversion Coating (b) and Captain Corrosion Conversion Coating reinforced by atomic layer deposited nanolaminate (c).

The Captain Corrosion Conversion Coating (CC) provided adequate protection against corrosion for AA 2024-T3 and AA 7075-T6 in a 168h ISO 9227 neutral salt spray (NSS) test. The coating had a thickness of up to 300 nm, was conductive and had excellent adhesion with the substrate materials (Fig.2a,b).

The reinforcement of the CC with a nanolaminate grown by ALD improved the corrosion resistance even further, retaining its conductivity and excellent adhesion. The new hybrid coating had a total thickness less than 1 μm (Fig.2c,d)

Figure 2. Scanning electron microscopy studies of glass bead blasted AA 2024-T3 with conversion coating (a,b) and conversion coating + ALD nanolaminate (c,d). Images a and c are made of the coating surface. Images b and d are taken from the FIB-made cross-section of the coating. For cross-sectioning, an additional protective Pt mask was added.

Based on the studies it was concluded that the new hybrid coating is likely suitable for industrial use but a scaling up study is required. Currently, the largest coated sample had a size less than 100 mm (Fig. 3.).