Improvement on Mechanical Properties of a bcc Matrix Al8(FeCuCrMn)92 High-Entropy Alloy by Phase Modulation of Interstitial Carbon Element

High-entropy alloys (HEAs) are novel multi-element alloys based on five or more constituent elements in a range of 5-35 at%. Here we present a method to improve strength of a body-centered cubic (bcc) matrix HEA without loss of ductility. The improvement was achieved by phase modulation combined other strengthening effect of interstitial carbon addition. Carbon addition can enhance strength and retain good ductility in some steels because carbon increases the volume fraction of face-centered cubic (fcc) phase. We used the same principle to design and fabricate a set of Al-8(FeCuCrMn)(92)C-x (x = 0, 1, 2, 3, 4 at%) HEAs under near-rapid solidification. Our results showed that carbon addition modulated constituent phases by increasing the volume fraction of fcc phase and carbides. As a result, addition of carbon increased yield strength of this bcc matrix HEA. But the ductility decreased, especially when carbon content was higher than 3 at%, which was ascribed to uneven distribution of Cu-rich fcc phase and carbides precipitated in bcc phase region. After annealing at 1173 K for 2 h, addition of 1 at% carbon improved yield strength without compressive fracture. It demonstrated that a proper carbon content addition with annealing can enhance the yield strength without loss of ductility for this bcc matrix HEA. Thus, interstitial carbon addition is a meaningful method to improve the mechanical properties by phase modulation combined other strengthening effect.