Overcoming intermediate-temperature brittleness via regulating trimodal γʹ structure in a novel multi-principal element alloy

Abstract

Solving the intermediate-temperature brittleness (ITB) of traditional superalloys and multi-principal element alloys (MPEAs) is a serious challenge. In this paper, a novel MPEA with superior mechanical performance is prepared and successfully overcomes the ITB by simple heat treatment. The effects of different solution treatments on the microstructure and mechanical properties of the alloy are studied. This work shows that the dendrite structure with trimodal γʹ structure is preserved by the subsolvus heat treatment. The heterogeneously distributed trimodal γʹ structure with high volume fraction primary γʹ phases in the interdendritic region effectively prevents the localized slip and enhances the pinning effect of grain boundaries, which inhibits the generation of ITB. The yield strengths of the MPEA with trimodal γʹ structure are 802 ± 17 MPa at 973 K, 814 ± 20.7 MPa at 1023 K and 776 ± 9 MPa at 1073 K, respectively, which are superior than that of most cast superalloys and MPEAs. Moreover, the elongations of the MPEA at 973 K, 1023 K and 1073 K are 10.6 ± 1.3 %, 14.2 ± 1.4 % and 11.0 ± 1.5 %, respectively, which increase by 214.9 %, 510 % and 219.4 %, respectively, compared with the MPEA with uniformly distributed bimodal γʹ structure. Meanwhile, the MPEA shows the best intermediate temperature plasticity (14.2 ± 1.4 %) at 1023 K due to the microstwinning. The scheme of combining MPEAs with the trimodal γʹ structure and microtwinning opens up a new avenue for the development and manufacture of advanced high-temperature structural materials.