MICROSTRUCTURE AND OXIDATION RESISTANCE OF Fe–Al–Nb ALLOYED LAYER ON 45 STEEL BY PLASMA SURFACE MODIFICATION

Abstract

The Fe–Al–Nb alloyed layer was coated on 45 steel by the plasma niobiumizing modification to improve the microstructure and oxidation resistance of Fe–Al coating prepared by hot-dipping aluminum. The alloyed layer growth followed the typical Volmer–Weber mode with the modification time growing (2–4 h), which was carried out at 1073[Formula: see text]K and pressure of 40[Formula: see text]Pa. Its surface morphology was compact without any defects, meanwhile, there was a transition layer between the Fe–Al–Nb alloyed layer and the substrate. The mass increase of Fe–Al–Nb specimen after oxidizing at 873, 973 and 1073[Formula: see text]K for 100[Formula: see text]h was less than that of the Fe–Al and untreated 45 steel specimen, it owed to the diffusing fully of the Fe, Al and Nb atoms during high-temperature oxidation, forming a compact protective Nb, Al-rich oxidation film on the surface of the Fe–Al–Nb alloyed layer, and the occurrence of the internal oxidation phenomenon between the loose iron oxides layer and the Fe–Al–Nb alloyed layer at 973[Formula: see text]K for 100[Formula: see text]h protected the internal coating from further penetration of oxygen. In addition, the Fe2Nb precipitates and Nb carbides dispersed through the alloyed layer, which were good for improving the strength, creep rupture resistance and inhibiting the Kendal effect at high-temperature.