Abstract:

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 510 nm 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 Y₂WO₆ 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 HV_0.2. Our work indicates that freeze-drying and subsequent low temperature sintering is a promising method for preparing high performance W-Y₂O₃ alloys.

Key words: W-Y₂O₃ alloys, Freeze-drying, Low temperature sintering, Ultrafine grains