Al0.3CrxFeCoNi high-entropy alloys with high corrosion resistance and good mechanical properties

The effects of the Cr content on microstructure, corrosion behavior, and mechanical properties of the Al0.3CrxFeCoNi high-entropy alloys (HEAs) were studied. The Al0.3CrxFeCoNi alloys with x = 0–1.0 exhibited the single face-centered-cubic (FCC) structure, and the alloys with x = 1.5–2.0 consisted of the FCC and disordered body-centered-cubic (BCC)/ordered BCC (B2) structure. In the 3.5 mass% NaCl solution, the Al0.3CrxFeCoNi alloys are spontaneously passivated, and the pitting resistance of the alloys was improved with increasing the Cr content in the alloys. It is notable that the Al0.3CrxFeCoNi (x = 1.5–2.0) alloys with Cr-rich FCC and BCC phases demonstrated excellent pitting-corrosion resistance and low corrosion rates of less than 10−3 mm/year due to the formation of the protective surface films enriched in Cr2O3. Moreover, the Al0.3CrxFeCoNi (x = 0–1.0) alloys with the FCC structure exhibited relatively-low tensile strength and large elongation. The further increase in the Cr content to x = 1.5–2.0 improved the strengths and hardness of the alloys due to the increase in BCC/B2 phases. The Al0.3CrxFeCoNi (x = 1.5–2.0) alloys with high corrosion resistance presented good mechanical properties, including tensile strengths of 640–1078 MPa and tensile elongations of 11–44%. It is also demonstrated that increasing the Cr content of Al–Cr–Fe–Co–Ni HEAs is an effective approach for tailoring corrosion-resistant HEAs.