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<p>This study investigates the effect of niobium addition on the microstructure, high-temperature oxidation behavior, and microhardness of (AlCrFeNi)<sub>100−x</sub>Nb<sub>x</sub> alloys (x = 0, 2, 4, 6, and 8 at.%) produced by arc melting. Thermodynamic calculations predicted the stability of A2 and B2 phases for all compositions and the formation of a C14 Laves phase in Nb-containing alloys, which was experimentally confirmed. The Nb-free alloy exhibited a lamellar A2/B2 microstructure, whereas Nb additions promoted dendritic microstructures with interdendritic regions containing A2, B2, and C14 Laves phases. Isothermal oxidation tests at 1000&#xa0;°C for up to 96&#xa0;h revealed a two-stage oxidation behavior, with an initial transient regime followed by slower mass gain kinetics. Although increasing Nb content led to higher mass gains, all alloys developed a continuous and adherent α-Al<sub>2</sub>O<sub>3</sub> scale, effectively protecting the base metal. The phase constitution remained unchanged after oxidation, despite microstructural coarsening. Microhardness increased systematically with Nb content due to the higher volume fraction of the C14 Laves phase, whereas high-temperature exposure reduced microhardness as a result of microstructural coarsening. Overall, the results highlight a trade-off between Nb-induced strengthening and oxidation resistance, indicating that controlled Nb additions provide a favorable balance between hardness, wear potential, and oxidation resistance for high-temperature applications.</p>

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Effect of Nb on the Microstructure, Microhardness and Oxidation Behavior of (AlCrFeNi)100-xNbx (x = 0,2,4,6 and 8 at.%) Alloys

  • 期刊论文

  • 发表日期：

    2026年6月3日

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  • Robson Leopoldino Ferreira,
  • Sebastião Vilas Boas,
  • Bruno Xavier de Freitas,
  • Antonio Augusto Araújo Pinto da Silva

摘要

This study investigates the effect of niobium addition on the microstructure, high-temperature oxidation behavior, and microhardness of (AlCrFeNi)100−xNbx alloys (x = 0, 2, 4, 6, and 8 at.%) produced by arc melting. Thermodynamic calculations predicted the stability of A2 and B2 phases for all compositions and the formation of a C14 Laves phase in Nb-containing alloys, which was experimentally confirmed. The Nb-free alloy exhibited a lamellar A2/B2 microstructure, whereas Nb additions promoted dendritic microstructures with interdendritic regions containing A2, B2, and C14 Laves phases. Isothermal oxidation tests at 1000 °C for up to 96 h revealed a two-stage oxidation behavior, with an initial transient regime followed by slower mass gain kinetics. Although increasing Nb content led to higher mass gains, all alloys developed a continuous and adherent α-Al2O3 scale, effectively protecting the base metal. The phase constitution remained unchanged after oxidation, despite microstructural coarsening. Microhardness increased systematically with Nb content due to the higher volume fraction of the C14 Laves phase, whereas high-temperature exposure reduced microhardness as a result of microstructural coarsening. Overall, the results highlight a trade-off between Nb-induced strengthening and oxidation resistance, indicating that controlled Nb additions provide a favorable balance between hardness, wear potential, and oxidation resistance for high-temperature applications.