In-situ fabrication and coating of oxide-dispersion-strengthened AlCoCrFeNi2.1 composite powders: Microstructure, mechanism, and properties

Abstract

To produce next-generation bonded coating composites for extremely high-speed laser cladding (EHLC) applications, there is an urgent demand to overcome the problems of spherical composite powder manufacturing. Here, we produced oxide-dispersion-strengthened (ODS) AlCoCrFeNi_2.1 eutectic high-entropy alloy (EHEA) composite powders in situ under different microaerobic conditions by gas atomization. The microaerobic conditions were regulated by the vacuum pressure (10⁻¹ Pa, 10 Pa, 20 Pa, and 30 Pa) before alloy melting. We also investigated the microstructures, properties, and in-situ oxidation mechanisms of the corresponding powders and coatings. The results showed that stable Y₂Hf₂O₇ particles and unstable Y₂HfO₅ striped oxides were formed in-situ at the L1₂-B2 phase interface in the Y/Hf co-doped AlCoCrFeNi_2.1 EHEA powders fabricated under microaerobic conditions. As the amount of oxygen was increased, the amount and size of the oxides in the powder also increased, which was accompanied by a transition in the oxide morphology from nanoparticles to a reticulated structure due to a higher O₂ diffusion rate in the coating. Additionally, a further transformation of the Y₂HfO₅ phase to the Y₂Hf₂O₇ phase occurred due to the secondary diffusion of O₂ during coating solidification. Compared with P = 10⁻¹ Pa, upon increasing the amount of oxygen by increasing the vacuum pressure from 10 Pa to 30 Pa, the oxidation rate constants of the corresponding coatings at 1100 °C increased by 1063.9 %, 80.3 %, and 16.4 %, whereas the spallation rates increased by 4847.7 %, 98.7 %, and 29.5 %, respectively. The coatings obtained at P = 10⁻¹ Pa showed superior high-temperature oxidation resistance compared with conventional NiCoCrAlY coatings.