Microstructure and improved corrosion properties of TP347H stainless steel via vacuum cladding high-entropy alloy coating

Developing advanced materials for high-temperature components in supercritical coal-fired boilers is essential for ensuring their longevity and safety. In this study, NiMoFeCoCrSiB high-entropy alloy (HEA) coatings were vacuum-cladded on the surface of TP347H steel. The result shows that the HEA coating is composed of an FCC (Bauhinia equiaxed crystal) + σ eutectic phase. The HEA coating exhibited strong metallurgical bonding with the substrate. Thermodynamic parameters (ΔHmix = −10.28 kJ/mol, ΔSmix = 15.07 J/(mol K), δ = 8.46%, Ω = 2.19) supported FCC + σ eutectic phase formation. In a 0.5 mol/l H2SO4 solution, compared with TP347H, HEACs showed greater arc resistance, lower Icorror (4.8 μA/cm2), and higher Ecorror (121.7 mV), whose impedance modulus |Z| (2070.29 W cm2) was 3.38 times that of the former. The average rate of corrosion for TP347H steel was 81.2 times that of the HEA coating in a 55% H2SO4 solution. TP347H steel showed severe and fast heterogeneous corrosion, while the HEA coating showed uniform corrosion. The improved corrosion resistance of the HEACs can be attributed to the comprehensive effect of both the passivation film and the FCC + σ eutectic phases. This study offers valuable insights for developing advanced materials for ultra-supercritical boiler tubes.