Role of stabilisers in the design of Ti aqueous suspensions for pressure slip casting

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Colloidal processing has long been used in ceramics to achieve green bodies with high densities, complex shapes and homogeneous microstructures, but they are rarely used to shape metal powders because of their high density and high surface reactivity. However, the possibility of processing fine particles makes these techniques interesting for metals, such as titanium, with a low density and high melting point. This work presents encouraging results in the design of aqueous suspensions of Ti particles to be shaped into bulk pieces by pressure slip casting (PSC), which opens new paths for the processing of fine and complex microstructures. Ti powders, measuring 10 μm in size, and mixtures of Ti and Al₂O₃ powders (added up to 5 wt.%) were dispersed in water by the addition of different stabilisers. The influence of the stabilisers in the slurry behaviour (in terms of nature, stereochemistry and active functional groups) was determined, as well as the incorporation of ceramic particles. A polyacrylic-based dispersant was selected as the best stabiliser to incorporate a second component (Al₂O₃) into the Ti suspension, whereas shear-thinning additives, such as TIRON, are preferred for PSC shaping. Suspensions with 1 wt.% Al₂O₃ were selected for processing composites by PSC and sintering. Sintered materials were characterised by measuring the density, oxygen content, hardness and microstructure analysis by SEM. Ti bulk pieces with 97% density and fine and homogeneous microstructure, of which the relationship between the oxygen content and hardness agrees with that measured for CPTi grade 4 (249 ± 24 HV30), can be processed by PSC.
Powder processing, Rheology, Composites, Titanium, Colloidal processing
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Powder technology, vol. 263 (Sept. 2014), pp. 81-88