Microstructure and properties of La₂O₃-doped tungsten-based bulk material and its densification mechanism during spark plasma sintering process

In the present work, the feasibility and effectiveness of fabricating La₂O₃-doped W-based bulk using W-based composite powders of core-shell structure with W particle as a core and La(OH)₃ as a shell, without hydrogen reduction treatment, was evaluated. La(OH)₃ was first coated on the surface of pure W (uncoated) powders at a weight percentage of 3.50% to prepare composite (coated) powders using the electroless plating method. The uncoated and coated powders without being treated by hydrogen reduction were then sintered using spark plasma sintering (SPS) to fabricate bulks. The results showed that the core-shell structure with W particle as a core and La(OH)₃ film as a shell was fabricated. La₂O₃-doped W-based bulk with about 2.93 wt.% La₂O₃ was obtained because of the transformation from La(OH)₃ to La₂O₃. The La₂O₃ particles with larger sizes were distributed mainly at W grain boundaries and those with smaller sizes were distributed mainly inside W grains. The major densification mechanism of the sintered bulk from coated powders was the filling effect of La₂O₃ particles on the pores as compared with the sintered bulk from uncoated powders, which could be evaluated by using a two-ball sintering neck model. The relative content of O in the form of WO₃ in the sintered bulk from coated powders was identical to that in the sintered bulk from uncoated powders. The W grain size of the sintered bulk from coated powders was smaller than that of the sintered bulk from uncoated powders. The thermal properties, mechanical properties, and irradiation properties of the sintered bulk from coated powders were all higher than those of the sintered bulk from uncoated powders. With the increase of sintering temperature, the evolution of the coated powders in the initial sintering period could be divided into six stages that were not completely independent and occurred in approximate sequence from the perspective of simplification. It was feasible and effective to fabricate La₂O₃-doped W-based bulk using the precursor W-based composite powders of core-shell structure with W particle as a core and La(OH)₃ as a shell without being treated by hydrogen reduction.