Effect of rare earth oxide addition on microstructure and mechanical properties of Ni-based alloy

Abstract

Oxide dispersion-strengthened (ODS) alloys possess several advantages such as excellent high-temperature creep strength and oxidation/irradiation resistance. Lanthanide oxides as well as yttria (Y2O3) have been proven to act as efficient additives in Fe-based ODS alloys; however, their potential for addition to Ni-based alloys has been limited. In this study, we fabricated four types of Ni-based ODS alloys with the combined addition of Ti and either Y2O3, cerium dioxide (CeO2), lanthanum oxide (La2O3), or gadolinium (III) oxide (Gd2O3) by mechanical alloying (MA) and hot isostatic pressing (HIP). We characterized both MA powders and HIPed samples of each alloy to compare the effect of oxide addition on the microstructure evolution. The results indicated that the addition of La2O3 had the most significant influence on refining oxide dispersoids and delaying recrystallization, resulting in a uniformly distributed ultra-fine grain structure. Based on further investigation of the contributions of various strengthening mechanisms, it was also found that the refinement of both oxide particles and grain size with the addition of La2O3 contributed to significant dispersion strengthening and grain boundary strengthening, leading to the highest Vickers hardness among the present alloys. When CeO2 and Gd2O3 were added, the mechanical properties were comparable, but better than those when Y2O3 was added. This demonstrates that all of the selected lanthanide oxides have practical potential as alternative additives to develop Ni-based ODS alloys, among which La2O3 would be the most advantageous in improving the mechanical properties.