Non-monotonous effect of pre-strain on the precipitates and strengthening mechanisms of high-entropy alloys

Pre-strain is often used as a powerful pre-treatment to tailor the microstructures and mechanical properties of traditional alloys. However, in high-entropy alloys (HEAs), the effect of pre-strain degree on the precipitates is still unclear. In this paper, we investigated the effects of pre-strain degree on the precipitation of Ni₂CoCrFeTi_0.18Al_0.12 high-entropy alloys. The HEAs were cold-rolled with different thickness reduction of 30%, 50%, and 70% and annealed at 800 °C for 30 ~ 60 min, followed by high-resolution scanning electron microscope (SEM) analysis. Counter-intuitively, we discovered a non-monotonous effect of pre-strain on the precipitation behavior, that low pre-strain can accelerate the precipitation behavior while such accelerating effect is weakened under high pre-strain. This non-monotonous effect is attributed to the shortened defects existing time by recrystallization under high pre-strain. In addition, pre-strain can controllably tailor the precipitation strengthening, dislocation strengthening, and grain boundary strengthening of HEAs. These results not only uncover the mechanism of the non-monotonous pre-strain effect on the precipitates but also provides a pre-strain mediated scheme for tuning the precipitation-strengthened HEAs to targeted properties.