The Role of Y₂O₃/Hf Co-Doping on the Microstructure and Tensile Properties of Alumina-Forming Co-Cr-Al-Ni ODS Superalloy

Abstract

Y₂O₃/Hf co-doping has been used to design novel alumina-forming Co-Cr-Al-Ni oxide dispersion strengthened (ODS) superalloys. In order to gain a deep understanding of the effect of Y₂O₃/Hf co-doping on the microstructure and mechanical properties of the superalloys, a comparative study of Co-20Cr-10Ni-15Al (at%) superalloys with and without the Y₂O₃/Hf co-doping fabricated by mechanical alloying (MA) and spark plasma sintering (SPS) has been carried out. The microstructure and the elemental distribution of the constituent phases of the two superalloys, in particular the distribution of fine oxide particles, were studied in detail by electron microscopy. Compared with a large grain size and coarse Al₂O₃ dispersoids in Y₂O₃/Hf-free alloy, Y₂O₃/Hf co-doping effectively refined the grains and inhibited the generation of Al₂O₃ particles through the preferential formation of fine Y₂Hf₂O₇ oxide particles. Y₂O₃/Hf co-doped alloy exhibited an ultrahigh ultimate tensile strength (UTS) of 1816 MPa, which is 240 MPa higher than that of the undoped Y₂O₃/Hf one owing to the dispersion strengthening of the dense Y₂Hf₂O₇ oxide particles as well as fine-grain strengthening. The fracture mechanism of Y₂O₃/Hf doped alloy during tensile loading was illustrated through transmission electron microscopy (TEM) observations and the optimization based on Y₂O₃/Hf doping content was proposed.