Enhanced high-temperature oxidation resistance of HfSi2-modified silicon based multilayer ceramic coating on Nb alloy prepared by a novel strategy

NbSi2/SiO2-Nb2O5/HfSi2-HfO2 multilayer ceramic coating containing Hf-rich out layers is designed and prepared on dense NbSi2 surface via pack cementation and subsequent liquid plasma-assisted particle deposition and sintering of HfSi2 particles to enhance oxidation resistance. The obtained ceramic layer contains the SiO2-Nb2O5 intermediate bonding-layer and the oxygen barrier outer-layer of HfSi2-HfO2. The mass gain of NbSi2/SiO2- Nb2O5/HfSi2-HfO2 coating (5.583 mg/cm2) is only 40 % compared to the NbSi2 coating (13.702 mg/cm2) after 100 h at 1200 degrees C. The HfO2 and HfSiO4 phases formed at high-temperatures are anchored in SiO2 scale, enhancing the structural stability of ceramic phase and blocking oxygen penetration. Namely, the Hf nail fixed on SiO2 scale effectively inhibits Nb-oxide growth and crack initiation.

Automated summary

A NbSi2/SiO2-Nb2O5/HfSi2-HfO2 multilayer ceramic coating with Hf-rich out layers was designed and prepared on a dense NbSi2 surface to enhance oxidation resistance. The coating showed a lower mass gain (40%) compared to the NbSi2 coating after 100 hours at 1200 degrees C. The presence of HfO2 and HfSiO4 phases anchored in the SiO2 scale improved the structural stability of the ceramic phase and blocked oxygen penetration, inhibiting Nb-oxide growth and crack initiation.