Influence of heat treatment on corrosion resistance of SLM-FeCoCrNiMo_0.3 high entropy alloy

Additive-manufactured FeCoCrNiMo_0.3 high-entropy alloys (HEAs) demonstrate promising corrosion resistance but suffer from inherent defects induced by selective laser melting (SLM). This study systematically investigates how annealing (500–1100 °C) regulates microstructural evolution and passive film properties in 1 M NaCl solution through electrochemical tests, immersion experiments, and multi-scale characterization (SEM/XPS/TEM). Key findings reveal: The 900 °C-annealed specimen exhibits optimal corrosion resistance with the lowest current density (0.0087 μA/cm²) and highest impedance modulus (1.6 × 10⁵ Ω·cm²), attributed to the nano-dispersed σ phase and dynamic repair mechanism of the Cr₂O₃-MoO₂ heterojunction. In contrast, 700 °C annealing triggers coarse σ-phase precipitation, establishing micro-galvanic couples that accelerate localized corrosion (mass loss rate: 0.0115 g/m²·h). The 1100 °C treatment causes severe Cr depletion at grain boundaries, increasing corrosion rate by 5.1 times compared to the optimal condition. XPS depth profiling confirms Mo⁴⁺ migration through oxygen vacancies facilitates in-situ passivation layer regeneration, while semiconductor analysis reveals n-type MoO₂ synergizes with p-type Cr₂O₃ to inhibit charge transfer across the film-electrolyte interface. These findings establish microstructure-property relationships governing SLM-HEA corrosion behavior and provide design guidelines for marine applications requiring chloride resistance.