Effects of Y2O3/Zr contents on microstructure and hardness of ODS-AlCrFeNi high-entropy alloys

Oxide dispersion-strengthened (ODS) AlCrFeNi high-entropy alloys with varying Y2O3 and Zr additions (0-5 wt %) were produced by mechanical alloying followed by spark plasma sintering. The influence of varying Y2O3 and Zr contents on the microstructure and hardness was investigated. The results showed that the types, average size and number density of the oxides are strongly dependent on the Y2O3 and Zr contents. In the 0YZ alloy, which lacks Y2O3 and Zr additions, Al2O3 with an average size of 20.2 nm and a number density of 2.48 x 1021/m3 is formed. In the 1YZ (containing 1 wt% Y2O3 and 1 wt% Zr), Al2O3 and Y4Zr3O12 are observed, with an average size of 11.9 nm and a number density of 5.2 x 1021/m3. In the 3YZ (3 wt% Y2O3 and 3 wt% Zr) and 5YZ (5 wt% Y2O3 and 5 wt% Zr) alloys, the observed oxides are exclusively Y4Zr3O12, with the average sizes of 10.9 nm and 17.1 nm, and the number densities of 1.11 x 1022/m3 and 6.24 x 1021/m3, respectively. The grain sizes of the 0YZ, 1YZ, 3YZ and 5YZ alloys are 268 nm, 182 nm, 140 nm and 191 nm, respectively. With increasing Y2O3 and Zr contents, the average grain and oxide sizes initially decrease (in the 0YZ, 1YZ and 3YZ alloys) and then increase (in the 5YZ alloy). The number density of oxides first rises (in the 0YZ, 1YZ and 3YZ alloys) and then declines (in the 5YZ alloy). Furthermore, the higher Zr content results in the formation of a Zr-rich phase in 5YZ. As the Y2O3 and Zr contents increase, the hardness of the alloy initially increases and then decreases. The 3YZ alloy exhibits the highest hardness value (732 HV). The influence of Y2O3 and Zr contents on the strengthening mechanism is analyzed.