Effect of Al Content on Microstructure, Mechanical, and Corrosion Properties of (Fe33Cr36Ni15Co15Ti1)100-xAlx High-Entropy Alloys

(Fe33Cr36Ni15Co15Ti1)(100-x)Al-x (x = 0, 3, 5, 6, 7, 8) high-entropy alloys (HEAs) are prepared by arc melting. The influence of Al element addition on the microstructure, mechanical properties, and anticorrosion in 3.5 wt% NaCl aqueous solution is systematically investigated. The microstructure analysis indicates that HEAs possess varying phases from face center cubic/face-centered cubic (FCC) + sigma to FCC + body-centered cubic (BCC) and then FCC + BCC + sigma, the last to BCC + sigma with the increase of Al content. The compressive results suggest that the Al addition exhibits a significant elevation in strength. Particularly, Al7 alloy shows a superior strength and plasticity, which presents a yield strength of 1315.3 MPa and a compressive strain over 50%. Order strengthening and coherent strengthening of nanosized phase are regarded as main strengthening effects. In addition, Al element is harmful for the corrosion resistance of (Fe33Cr36Ni15Co15Ti1)(100-x)Al-x HEAs system, which is ascribed to the weakened passive film stability. It is also noted that pits tend to be initiated in relatively Cr-depleted phases (FCC or B2 phase) due to the inhomogeneous elemental distribution-induced galvanic corrosion. In spite of this, all HEAs exhibit superior corrosion resistance than that of 304SS.