Synthesis of W-Y2O3 alloys by freeze-drying and subsequent low temperature sintering: Microstructure refinement and second phase particles regulation

In this work, W-Y2O3 alloys are prepared by freeze-drying and subsequent low temperature sintering. The average size of reduced W-Y2O3 composite powders prepared by freeze-drying method is only 18.1 nm. After low temperature sintering of these composite nanopowders, the formed W-Y2O3 alloys possess a smaller grain size of 510nm while maintaining a comparatively higher density of 97.8%. Besides a few submicron Y2O3 particles (about 100-300 nm) with a W-Y-O phase diffusion layer on their surface distribute at W grain boundaries, lots of nano Y-2 WO6 particles (<20 nm) exist in W matrix. Moreover, many Y6WO12 (<10 nm) particles exist within submicron Y2O3 particles. The formation of these ternary phases indicates that some oxygen impurities in the W matrix can be adsorbed by ternary phases, resulting in the purification of W matrix and the strengthening of phase boundaries. The combined action of the above factors makes the hardness of the sintered W-Y2O3 alloys in our work as high as 656.6 + 39.0 HV0.2. Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y2O3 alloys. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.