Corrosion Resistance of Boronized Carbon Steel in a Galinstan-Refrigerant Two-Phase Agitated System

This study experimentally evaluates, for the first time, the corrosion resistance of boronized carbon steel in environments containing liquid Galinstan (GaInSn) and selected organic refrigerants (n-pentane and R1233zd-(E)) at 150 °C for up to 80 days. The tests simulated gas-liquid-metal two-phase exposure under pseudodynamic conditions, where the test coupons and corrosive media were mechanically agitated. These conditions are relevant to advanced liquid-metal heat-transfer systems. Cross-sectional microstructural analysis revealed a uniform 180-200 μm thick FeB-Fe₂B bilayer coating exhibiting a distinctive sawtooth morphology associated with strong adhesion to the substrate. Optical microscopy, hardness determination, and ICP-OES analysis indicated that the iron boride coating maintained its structural integrity after exposure. No evidence of surface degradation (e.g., cracking, caverns, peeling) or substrate degradation was observed by the employed characterization techniques. The coating thickness and microhardness showed no systematic decrease after exposure, remaining at their original levels. ICP-OES analysis revealed negligible concentrations of boron and iron (0.01-0.03 wt %) in the exposed Galinstan, with no systematic increase. Collectively, these observations indicated that no significant degradation or dissolution of the iron boride coating was detected during up to 80 days of exposure under the investigated conditions. In contrast, previously reported studies of SS316 identified measurable degradation under comparable conditions after only 20 days. These findings suggest that iron boride coatings warrant further investigation as a potentially cost-effective material option for selected liquid Galinstan-based heat-transfer systems. Additional studies involving larger sample populations, higher temperatures, longer exposure durations, and true dynamic flow conditions are required to further assess long-term performance and application potential.