The influence of Nb addition on the passivity of CoCrNiNbx multi-principal element alloys

The effect of Nb addition on the passivation behavior of CoCrNiNbx (x = 0 similar to 0.5) multi-principal element alloy (MPEA) were investigated with surface characterization and electrochemical techniques. With the addition of Nb, the Nb-riched HCP dendrite phase gradually precipitates from the original FCC phase. The corrosion resistance of CoCrNiNbx MPEAs increases firstly and then starts to decrease, reaching an optimal value at x = 0.2. XPS depth profiles and ToF-SIMS characterization of the surface passive films demonstrate that the film structure is transformed from a single layer to the bilayer which consists of a Cr-enriched outer layer and an Nb-enriched inner layer. Analysis of the pitting and passivation behavior of the CoCrNiNbx MPEAs suggests that a moderate content of Nb thickens the passive film, promotes the production of Nb oxides and Cr2O3, and thus stabilizes the passive film and finally reduces pitting sensitivity.

Automated summary

The addition of Nb has a significant effect on the passivation behavior of CoCrNiNbx alloy. An appropriate amount of Nb can improve the corrosion resistance of the alloy by thickening the passive film and promoting the formation of Nb oxides and Cr2O3. This has important implications for the stability and pitting resistance of the alloy.