This study synthesized FeNiCuAlX high-entropy alloys (HEAs) (where X = Cr, Co, Mn) using arc melting and investigated their high-temperature oxidation behavior in air at 900 °C. The oxidation kinetics of all alloys followed a parabolic rate, with the oxidation rate constants (kp) of FeNiCuAlCr, FeNiCuAlCo, and FeNiCuAlMn being approximately two to three orders of magnitude lower than that of the FeNiCu alloy. Specifically, FeNiCuAlCr exhibited the lowest kp value of 1.72 × 10⁻⁶ mg²·cm⁴/s, which is significantly lower than those of FeNiCuAlCo (3.29 × 10⁻⁶ mg²·cm⁴/s) and FeNiCuAlMn (1.71 × 10⁻⁵ mg²·cm⁴/s). This suggests that the addition of chromium promotes the formation of a dense Al₂O₃/Cr₂O₃ oxide layer, significantly enhancing the oxidation resistance. Furthermore, corrosion resistance was assessed through potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution. FeNiCuAlCr demonstrated exceptional resistance to localized corrosion, as indicated by its low corrosion current density (45.7 μA/cm²) and high pitting potential (−0.21 V), highlighting its superior corrosion performance.

The demand for metallic nickel has been growing steadily. Laterite nickel ore, as an oxide mineral, contains a higher nickel content than sulfide ores, enabling more economical smelting in the nickel extraction process. However, an extremely thick slag layer generated during side-blown smelting of laterite nickel ore alters the bath circulation characteristic of conventional smelting processes. To address this, this study employs a validated Multi-Fluid VOF model to analyze the flow field characteristics of the side-blown furnace bath under varying slag layer thicknesses. Within the slag thickness range of 1.5–2.5 m, the ascending air plume shifts horizontally along the furnace wall with increasing slag thickness, entraining matte into the slag and promoting its diffusion toward the settling zone. Matte diffusion is governed by bath circulation: backflow from the settling zone dominates at lower slag thickness, while vertical kinetic energy from splashed melt reflux dominates at higher thickness. This reflux-induced circulation is blocked by the dense matte layer, causing no disturbance to the bottom matte and thus favoring slag–matte separation. Increasing slag thickness raises the near-wall circulation zone and plume entry point, reducing gas holdup near the tuyere and weakening oxygen–matte contact.