High-entropy MAX phase with ultrahigh strength and large plasticity mediated by local chemical fluctuations

Abstract

MAX phases are an emerging kind of material with a unique combination of metallic and ceramic properties, and they have great potential to be utilized as high-temperature components. However, their lack of plastic deformation capability and low strength (particularly at high temperatures) result in unsatisfactory mechanical properties, which restricts their potential applications. In this study, we introduced local chemical fluctuations (LCFs) into atomic packing layers of MAX phases by applying the high-entropy concept learned from the metal community. We substituted Ti in the model Ti₂AlC MAX phase with Zr, Nb, and Ta and successfully developed a high-entropy MAX phase (TiZr_0.6NbTa)₂AlC while preserving its lattice structure. The enhanced LCFs in this new MAX phase created strong lattice strains, increasing the resistance to dislocation slip and then leading to a high compressive yield strength of over 500 MPa even at 1473 K. Also, the LCFs stimulated cross-slips and stacking faults during deformation, effectively alleviating strain localization, promoting uniform deformation, and eventually enhancing plasticity at room temperature and the elevated temperature. Our work not only sheds light on understanding the deformation mechanisms of MAX phases in general, but also offers a valuable route for improving their mechanical properties, making them competitive as the next-generation lightweight high-temperature materials.