Fe-Cr-Si Codeposition on Nb-Si based Alloys via Halide Activated Pack Cementation to Improve Oxidation Resistance

Abstract

The coating formation by Fe-Cr-Si codeposition was done in a single step via Halide Activated Pack Cementation (HAPC) on Nb-Si alloy with the aim of improving the oxidation resistance. The activator salt and temperature selections for HAPC process were obtained by thermodynamic analysis. The isothermal oxidation test results for the coated alloy at 1200 °C for 62 h showed good oxidation resistance. The mass gain was 17.5 mg/cm². Furthermore, no cracks and spallation on the oxide layers were observed for the coated alloy after the oxidation test, being that the oxidative kinetics curve is in accordance with the parabolic rate law. On the other hand, total oxidation was observed for the uncoated alloy after 12 h at 1200 °C in the isothermal oxidation test. The mass gain was 49.27 mg/cm² and several cracks and spallation on the oxide layers led to a severe oxidation process.

Keywords:
Nb-Si based alloys; Halide Activated Pack Cementation (HAPC process); Fe-Cr-Si Codeposition; Thermodynamic Analysis; Oxidation Resistance