Process Focus: Silicide Coating

Are your nights haunted by worries about oxidation of niobium alloys at high temperatures? 

Ours were.

We’d turn on the bedside light and reach for a book that will put us back to sleep. Something about metallurgy we’d already read before. The light would wake up our spouse, who would sleepily ask, “Niobium again?”

We’re all sleeping better now, and it’s thanks to silicide coating.

What problem does silicide coating solve?

As science and engineering have pushed the boundaries of speed and power in things like rocket engines and burn motors, they have turned to specialized alloys containing metals that can withstand very high temperatures, like niobium and molybdenum. Niobium is popular in aerospace alloys due, among other things, to its high strength even at extreme temperatures. 

The problem with these metals is they are prone to oxidation even at relatively low temperatures. Oxidation is a chemical reaction in which a material loses electrons. As temperatures rise, so does the speed of oxidation. The oxidized layer on a niobium alloy forms a brittle scale, which degrades performance and can lead to component failure.

It’s a problem that has sent aerospace engineers back to the drawing board quite a few times.

Protective coatings are the solution to oxidation problems. The challenge for engineers of a component like the thrust nozzle of a rocket engine is how to produce a uniform coating that can also withstand operating temperatures that only a lava monster could love.

Silicide coating is one answer. As the name suggests, silicide coatings are produced using compounds of silicone. The specific compounds used vary according to the process alloys and engineering objectives. A silicide coating provides a high-strength protective layer that drastically reduces oxidation even of high-oxidation alloys like niobium.

Rise of the silicide coating machines

Silicide coating can be accomplished in several ways. Some shops will spray it on. Don’t get the wrong idea: this isn’t like watering the petunias on the front lawn, unless you go for that messy look to keep the door-to-door salespeople away. Properly executing a spray coat requires careful measurements and precise operation, but it doesn’t always yield optimal results.

Thermal-Vac has developed a different way of doing things.

In so much of what we do, automation isn’t a viable option. It’s expensive and doesn’t always produce the results you want. But for silicide coating, it’s the best approach we’ve found.

Thermal-Vac has developed a proprietary process for consistently producing highly uniform, strictly controlled silicide coatings. A robotic arm dips the component into the silicide slurry, which is maintained with strict composition requirements to ensure uniform thickness and deposition. The newly coated part is placed in a vacuum furnace, where it’s cooked at 2580 °F to diffuse the slurry into the component surface. 

The robot arm gives a thumbs-up when the diffusion process is done—it’s a big fan of Terminator 2.

We have worked tirelessly to dial in every detail of our silicide coating process to ensure a reliable result even with conventionally difficult parts. The dip process delivers uniform thickness, which makes aerospace engineers happy. Our process is approved by the aerospace industry for Type 512A and 512E silicide coatings.

Thermal-Vacs got you coated

Innovations like our silicide coating process are a key reason why Thermal-Vac is a recognized leader in the industry. If you’re interested in knowing more about how we work, or if you’re looking for coating solutions you can’t seem to find anywhere else, give Thermal-Vac a call

The robot is standing by.


Thermal-Vac has received certified recognition by these top accreditation programs.

  • Heat Treating