Porous W-10 wt% Ti alloys are prepared by freeze-drying a WO₃-TiH₂/camphene slurry, using a sintering process. X-ray diffraction analysis of the heat-treated powder in an argon atmosphere shows the WO₃ peak of the starting powder and reaction-phase peaks such as WO_2.9, WO₂, and TiO₂ peaks. In contrast, a powder mixture heated in a hydrogen atmosphere is composed of the W and TiW phases. The formation of reaction phases that are dependent on the atmosphere is explained by a thermodynamic consideration of the reduction behavior of WO₃ and the dehydrogenation reaction of TiH₂. To fabricate a porous W-Ti alloy, the camphene slurry is frozen at -30°C, and pores are generated in the frozen specimens by the sublimation of camphene while drying in air. The green body is hydrogen-reduced and sintered at 1000°C for 1 h. The sintered sample prepared by freeze-drying the camphene slurry shows large and aligned parallel pores in the camphene growth direction, and small pores in the internal walls of the large pores. The strut between large pores consists of very fine particles with partial necking between them.

An optimum route to synthesize Ti-Mo system powders is investigated by analyzing the effect of the heat treatment atmosphere on the formation of the reaction phase by dehydrogenation and hydrogen reduction of ball-milled TiH₂-MoO₃ powder mixtures. Homogeneous powder mixtures with refined particles are prepared by ball milling for 24 h. XRD analysis of the heat-treated powder in a hydrogen atmosphere shows TiH₂ and MoO₃ peaks in the initial powders as well as the peaks corresponding to the reaction phase species, such as TiH_0.7, TiO, MoO₂, Mo. In contrast, powder mixtures heated in an argon atmosphere are composed of Ti, TiO, Mo and MoO₃ phases. The formation of reaction phases dependent on the atmosphere is explained by the partial pressure of H2 and the reaction temperature, based on thermodynamic considerations for the dehydrogenation reaction of TiH₂ and the reduction behavior of MoO₃.

Citations

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• Effect of titanium addition on mechanical properties of Mo-Si-B alloys
  Won June Choi, Seung Yeong Lee, Chun Woong Park, Jung Hyo Park, Jong Min Byun, Young Do Kim
  International Journal of Refractory Metals and Hard Materials.2019; 80: 238.     CrossRef