Simultaneous strength and ductility enhancement in Co29Cr31Cu4Mn15Ni21 high entropy alloy through fully coherent nano-precipitates

Abstract

High strength and high ductility are fundamental goals for metallurgists in developing metal structural materials. However, enhancing material strength often leads to a corresponding reduction in ductility, a phenomenon known as the trade-off effect. This study has successfully introduced fully coherent nano-precipitates into the Co 29 Cr 31 Cu 4 Mn 15 Ni 21 high-entropy alloy (HEA) through an optimized aging heat treatment process at 500 °C for 4 h. The results of tensile mechanical tests indicate that the strength and ductility are improved after incorporating these nano-precipitates. The yield strength increased from 315 MPa to 400 MPa, representing a 27 % enhancement. Significantly, this enhancement in strength was attained without compromising ductility, as evidenced by an increase in elongation from 53 % to 56 %. These findings effectively challenge the conventional trade-off effect between strength and ductility. Furthermore, the study underscores the critical importance of the aging heat treatment parameters in enhancing the mechanical properties. It was observed that excessive heat treatment duration or elevated temperatures can lead to the formation of detrimental σ phases, which adversely affect the mechanical performance. This research contributes valuable insights for further enhancing the mechanical properties of HEAs, thereby promoting their potential applications in industrial settings. • Uniformly distributed coherent nano-precipitates are successfully introduced into the Co 29 Cr 31 Cu 4 Mn 15 Ni 21 HEA through aging heat treatment. • The mechanical test results indicate that the Co 29 Cr 31 Cu 4 Mn 15 Ni 21 HEA aged at 500 °C for 4 h exhibits simultaneous improvements in both strength and plasticity, effectively overcoming the traditional trade-off effect. • Excessive aging time or elevated aging temperatures can result in the formation of not only nano-precipitates but also potentially harmful second phases, such as the σ phase. • When the σ-phases are formed at the grain boundaries, which are detrimental to the mechanical properties of the alloys.