Fabrication of Mo-Y₂O₃ alloys using hydrothermal synthesis and spark plasma sintering

Fine-grained Mo alloys doped with uniformly distributed nanoscale Y₂O₃ particles were successfully prepared by employing two powerful strategies: fabricating high-quality precursor powders using hydrothermal synthesis and subsequent powder consolidation by spark plasma sintering (SPS) technique. In this study, the effect of hydrothermal variables on the morphology and existent form of yttrium and Mo was systematically studied, and the refinement mechanism of reduced mixing powders and the densification under the different sintering parameters were investigated. The results show that spherical Y₂(CO₃)₃·2H₂O gradually replaced Y(OH)CO₃ owing to the increased concentration of hydrogen bonds and CO₃²⁻ at excess alcohol and urea, and lamellar (NH₄)₂Mo₄O₁₃ developed into large pillar-shaped h-MoO₃ with decreasing pH. Due to the low calculated lattice mismatch degree of Mo/Y₂O₃ interfaces ~10.9%, Y₂O₃ particles further refined and homogenized the reduced mixing powders as heterogeneous nucleating sites. After sintering at 1700 °C for 5 min with a heating rate of 100 °C/min, Mo-Y₂O₃ alloys possessed fine grains of 1.80 ± 0.17 μm, a high density of 98.18% and the high indentation hardness of 314.77 ± 26.12 HV_0.3 and 4.82 ± 0.53 GPa H_IT. The Y₂O₃ particles were uniformly distributed in the Mo matrix, and semi-coherent with Mo lattice, with the orientation relationships as follows: (010)_Y2O3//(011)_Mo, (01-1)_Y2O3//(020)_Mo, and [100]_Y2O3//[100]_Mo.