Unprecedented bake hardening responses of interstitial high-entropy alloy by synergistic effect with lattice distortion

High-entropy alloys (HEAs) composed of multiple principal elements have attracted considerable interest in recent decades as a new class of metallic materials. Among them, the equi-atomic CoCrFeMnNi HEA system has great potential for application as a structural material due to its excellent properties in various fields, but it has a drawback of relatively low yield strength (YS) at room temperature. Here, for the first time, we propose the bake hardening (BH) as a breakthrough to overcome the relatively inferior YS of the CoCrFeMnNi HEA system. We found that the carbon-added CoCrFeMnNi HEAs are not only bake-hardenable, but also exhibit unprecedented BH responses than conventional bake-hardenable materials, with BH responses up to 120.0 MPa depending on the carbon concentration in the matrix. It is the outcome of the mutual synergistic effect between the massive solid solution strengthening characteristic from lattice distortion of the HEAs and the Cottrell atmosphere generated during the BH process. This study demonstrates that the carbon-added CoCrFeMnNi HEAs are more advantageous to apply the BH effect than conventional bake-hardenable materials, which suggests the possibility of industrialization of various interstitial HEA systems as well as carbon-added CoCrFeMnNi HEAs.