Effect of alloying elements on the microstructure and high-temperature oxidation behavior of yttrium-based alloys

Abstract

Yttrium hydride is recognized as an effective neutron moderator material due to its superior thermal stability and high hydrogen retention capability at elevated temperatures. In this study, the influences of alloying elements Zr, B, and Dy on the microstructure, microhardness, and high-temperature oxidation resistance of yttrium-based alloys were systematically investigated. The primary objective was to mitigate cracking issues encountered during hydrogenation and subsequent operational applications of these alloys. Yttrium-based alloys with varying compositions were fabricated through vacuum arc melting. The microstructure and phase composition of these alloys were characterized. Experimental results revealed that Dy was solid dissolved in the Y matrix for solid solution strengthening, while Zr with limited solubility precipitated as α-Zr for second-phase strengthening, both significantly improving the alloy hardness. Simultaneously, grain refinement is achieved through the formation of YB₂ and ZrB₂ compounds by the B element, leading to further optimization of mechanical properties. High-temperature oxidation experiments conducted at 900 °C revealed that optimal oxidation resistance was exhibited by B-containing alloys (Y-1.2B and Y-1.2B-5Dy), attributable to the formation of highly stable borides at grain boundaries. In contrast, antioxidant performance was found to be degraded due to grain boundary corrosion exacerbated by preferential oxidation of Zr elements. The formation of a composite oxide layer consisting of Dy₂O₃ and Y₂O₃ was observed upon Dy element addition, resulting in effective suppression of oxygen diffusion and consequent significant improvement in the alloy's high-temperature stability. Through comprehensive performance evaluation, Y-1.2B and Y-1.2B-5Dy alloys were identified as exhibiting superior characteristics in terms of microstructure, hardness, and oxidation resistance, thereby establishing them as promising candidate systems for advanced neutron shielding material research.