Phase transformation and strengthening mechanism investigation of CrFeMnNi(2-x)Tix high entropy alloys

Understanding the intricate phase transformations and their impact on the mechanical properties holds paramount importance in developing high entropy alloys (HEAs) with ideal properties, yet it remains challenging and underexplored. In this study, a series of novel CrFeMnNi_(2-x)Ti_x (x = 0, 0.5, 1, and 1.5 at.%) HEAs were meticulously designed based on the established Valence Electron Concentration (VEC) rule, with the VEC values systematically varied as the atomic composition (Ni, Ti) changed. The microstructure, phase transformation behavior, mechanical properties, and strengthening mechanisms were systematically investigated. We found that the HEA powders exhibited phase behavior consistent with the VEC rules. The spark plasma sintered (SPSed) HEA bulk samples exhibited a phase transformation attributed to the precipitation of Cr and Mn within the matrix, resulting in the formation of the σ phase. Quantitative calculation of the strengthening mechanisms revealed that grain boundary strengthening and precipitation strengthening were the primary contributors to the high strength of the HEA bulk samples. These findings not only advance the utilization of the VEC rules in HEA material design but also contribute to the understanding of the phase behavior and mechanical properties of HEAs, facilitating the design of high performance HEAs.