Effects of Y2O3 nanoparticles / Ni matrix interface on the mechanical properties and helium swelling resistance in NiMoCr-Y2O3 alloys

Abstract

The use of oxide dispersion-strengthened (ODS) nickel-based alloys has emerged as a promising choice for structural materials in molten salt reactors. In this study, a novel Y2O3 nanoparticles dispersion-strengthened nickel-base alloy was prepared by powder metallurgy method. The NiMoCr-Y2O3 alloy exhibits superior yield strengths and ultimate tensile strengths, surpassing those of the Hastelloy N (HN) alloy, both at room temperature and high temperatures. This enhancement can be attributed to the dispersion-strengthening effect imparted by Y2O3 nanoparticles. Additionally, the NiMoCr-Y2O3 alloy displays commendable plasticity. Nevertheless, it is worth noting that the stress concentration at the Y2O3 nanoparticles/Ni matrix interfaces makes it susceptible to stress-induced breakage, resulting in lower plasticity compared to the HN alloy. Transmission electron microscopy (TEM) observations reveal that the Y2O3 nanoparticles /Ni matrix interfaces effectively trap helium (He) bubbles, leading to a reduction in helium bubble size. Furthermore, X-ray absorption fine structure (XAFS) analysis indicates a higher vacancy density in NiMoCr-Y2O3 alloy compared to HN alloys during irradiation, contributing to an increased number of helium bubbles in the NiMoCr-Y2O3 alloy. This effect is primarily due to the preferential absorption of a significant quantity of interstitial particles by the Y2O3 nanoparticles/Ni matrix interfaces. Consequently, the volume fraction of helium bubbles in the NiMoCr-Y2O3 alloy (∼0.12 %) is notably lower than that observed in the HN alloy (∼0.52 %), showing that NiMoCr-Y2O3 alloys exhibit excellent He swelling resistance.