Power-law aging strengthening by local chemical ordering in (CoCrNi)93Al4Ti2Nb high-entropy alloy

The incipient plasticity of the (CoCrNi)₉₃Al₄Ti₂Nb high-entropy alloy, which contains varying degrees of local chemical ordering (LCO), is detected using nanoindentation. Statistical results of the critical strength for incipient plasticity exhibit bimodality. After deconvolution analysis, the average strength and activation volume of each peak reveal that the incipient plasticity is controlled by homogeneous dislocation nucleation and vacancy-induced heterogeneous dislocation nucleation. As the aging time increases, the critical strength for incipient plasticity gradually rises, and the strength increment compared to the homogenized sample follows a power-law relationship with aging time. Given the high similarity with the variation in hardness increment caused by precipitates, it is hypothesized that the evolution of LCO is similar to that of the precipitates. The constant describing the phase transformation type suggests LCO is in the initial phase transformation stage, leading to the inference that LCO may serve as a precursor to the precipitates.