Preparing high-temperature oxidation-resistant ceramic coatings on niobium and niobium alloy substrates is a key surface technology to extend their excellent high-temperature strength for applications in oxygen-containing environments. The core challenges in this field lie in resolving the enormous thermal stress caused by the mismatch in thermal expansion coefficients between metals and ceramics, as well as ensuring interfacial chemical compatibility to prevent coating cracking and spallation during thermal cycling.

To achieve reliable protection, a precisely designed gradient system of “niobium substrate – functional transition layer – ceramic top layer” must be adopted. The key technology involves in-situ formation of a continuous silicide interlayer (e.g., NbSi₂) on the substrate through processes such as siliconizing. This interlayer not only forms a strong metallurgical bond with the substrate but also has a thermal expansion coefficient intermediate between the two materials, effectively relieving thermal stress while acting as a diffusion barrier to inhibit oxygen penetration. On top of this optimized interlayer, functional ceramics with low oxygen diffusivity and excellent thermal stability (such as mullite) are deposited as the final barrier. This comprehensive synergistic protection system has successfully enabled niobium alloy components to be used in cutting-edge fields subjected to extreme high temperatures and thermal shocks, including rocket engine nozzles and advanced gas turbine blades.

Below is the sample preparation scheme for this application. The main challenge lies in polishing ceramic coatings that are prone to cracking and spallation:

1️⃣ Rough grinding: P2500 silicon carbide sandpaper with low-temperature wax applied to the surface;

2️⃣ Fine grinding: P4000 silicon carbide sandpaper with low-temperature wax applied to the surface;

3️⃣ Rough polishing: ET-JP polishing cloth + 3μm aluminum oxide;

4️⃣ Fine polishing: ZN-JP polishing cloth + 50nm silica.

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