Thermal Barrier Coatings (TBC) for more than 650°C

Since 2019, WZR has been working on the topic of TBC systems (Thermal Barrier Coating). The aim of such coatings is to protect the substrate (typically metals) from high temperatures. This is achieved by using temperature-resistant materials with very low thermal conductivity. The application temperature of such systems is significantly higher than previously developed coating systems, which WZR calls CerCoat®-H, -Y and -P. All these systems are based on sol-gel processes that require a minimum curing temperature of 190°C and have a maximum application temperature of approx. 450°C.

The newly developed high temperature resistant coatings are now called CerCoat®-HT. The basis is a ceramic suspension that enables adhesion to metallic substrates with special binders. A temperature-resistant bonding is achieved by a heat treating process between 500°C and 650°C, which ensures the subsequent application temperature up to at least 650°C.

Due to its low thermal conductivity and special structure, yttria-stabilised zirconia (YSZ) is the most commonly used material for TBC systems. WZR follows the approach of mixing alumina with special hollow spheres and thereby achieving high thermal insulation with simultaneous high temperature resistance.

The new coating system can be applied by dip coating as well as by spray coating. Spray coating is often preferred because it enables the coating of complex geometries and the layer thickness can be varied as required.

Our TBC coatings are characterised by the following properties:

• Low thermal conductivity of app. 0,4 W/m K @ 700°C
• Layer thickness from 100 to 200 µm
• Heat treatment tested up to 650°C
• Very good adhesion measured by cross-cut test: Rating 4 to 3 according to ASTM D3359
• Very good thermal shock resistance determined in thermal shock tests
• Ageing of samples for 100h at 600°C: without findings

Both dip coating and spray coating are suitable coating processes. Spray coating is often preferred because it allows the coating of complex geometries and the layer thickness can be applied as desired.

The cross-cut test was evaluated according to DIN EN ISO 2409 and ASTM 3359. The following figure shows the GS tester used on the left. The illustration in the middle shows an overview of a tested sample, the illustration on the right shows the surface magnified 25 times. The very good adhesion of the coating to the substrate can be seen clearly.