Grain/phase boundary engineering and high Cr contents enhancing oxidation resistance of dual-phase multi-principal component alloys

The oxidation behavior of dual-phase FeCrNiAlTi multi-principal component alloys (MCAs) with tailored grain/phase boundaries (GBs/PBs) lengths was systematically investigated by isothermal oxidation at 800℃ in air. Experimental results demonstrate that GBs/PBs engineering, when coupled with chemical composition tuning, yields a significant enhancement of oxidation resistance. The alternating distribution of face-centered cubic (FCC) and body-centered cubic (BCC) grains with short interphase distances facilitates lateral oxide growth along boundaries, promoting the formation of a continuous oxide film. Specifically, prolonged GBs/PBs lengths (up to 320.472 mm⁻¹) and high Cr content in BCC phases (54.20 %) accelerate the diffusion kinetics of protective elements (Al/Cr) during initial oxidation, enabling rapid formation of dense, continuous oxidation scales composed of Al₂O₃ and Cr₂O₃. Notably, the continuous Al₂O₃ layer acts as an effective barrier, suppressing subsequent outward Cr diffusion and inward oxygen ingress, thereby decelerating oxidation kinetics (parabolic rate constant k_p = 0.19 ×10⁻³ mg²·cm⁻⁴·h⁻¹) and outperforming many previously reported MCAs. This work highlights that GBs/PBs engineering, coupled with chemical composition adjustment, offers a viable pathway for developing high-performance MCAs for high-temperature structural applications.