Evolution of Guinier-Preston zones in cold-rolled Al0.2CoCrFeNi high-entropy alloy studied by synchrotron small-angle X-ray scattering

The synchrotron small-angle X-ray scattering (SAXS) technique was used to investigate the morphological evolution of Guinier-Preston (GP) zones in 80% cold-rolled Al0.2CoCrFeNi high-entropy alloy aged at 550 degrees C for different times. The hardness profile exhibited double-peaked aging behavior. HRTEM observations revealed the appearance of the GP zones in specimens aged for two peak aging times. The SAXS analysis demonstrated that, according to their evolutions of relative volume fraction and size, the two groups of GP zones could be divided into GP1 and GP2 zones from 1 h of aging. The corresponding peaks in volume fraction and in size of GP1 and GP2 zones were correlated to the first and the second peak aging, respectively, indicating precipitation hardening by GP1 and GP2 zones. In addition, mechanical properties measured by tensile tests showed a trend similar to that of the hardness variation. The increasingly large particles after 1 h of aging detected by SAXS were also observed by TEM in 100 h over-aged specimens and identified as an AlNi-rich L1(2) phase. Based on the combined investigations of SAXS and TEM, the precipitation sequence in 80% cold-rolled Al0.2CoCrFeNi alloy aged at 550 degrees C is GP1 -> GP2 -> L1(2).