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

Abstract

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 *Abstract 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. KeywordsPowder processing, Rheology, Composites, Titanium, Colloidal Processing AbstractColloidal 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. Sinter...

Improvement of TiN nanoparticles EPD inducing steric stabilization in non-aqueous suspensions

“…In view of the thermal characterization of the TiN powders, the heat treatments of TiN coatings obtained after deposition times of 2 and 3 min on AISI 316L stainless steel were carried out at 1200 • C for 1 hour in vacuum in order to consolidate the TiN structure avoiding oxidation [45]. The EPD coatings thermally treated were prepared with the suspension stabilized with PEI-25,000 and the addition of 0.66 wt.% of hydrazine.…”

Ti/Ti3SiC2(/TiC) Bulk and Foam Composites by Pyrolysis of Polycarbosilane and TiH2 Mixtures

“…The pure TiH 2 slurry exhibited a strong thickening behavior derived from the irregular morphology of the particles, which also gave an irregular distribution of charges at their surfaces due to their crystalline anisotropy. Similarly to what happens for Ti slurries, the flow behavior of the TiH 2 aqueous suspensions suggested the formation of networks among particles when the shear rate increased, and consequently demonstrated a lack of stability. The thickening and the flow complexity of the TiH 2 slurries would affect shaping (foaming) and particles packing, as well as the homogeneity of the suspensions, especially, when high shear techniques such as milling or mechanical stirring are used.…”

“…Contrarily, colloidal processing techniques have demonstrated to be a valuable tool to overcome the low compressibility of Ti powders with small particle size (<10 μm). In aqueous suspensions, the surface of Ti particles passivizes, and preliminary results show that processing of Ti through colloidal suspensions does not increase the oxygen content in the final material, promoting the densification of a microstructure with lower grain size than that achievable with conventional powder metallurgic (PM) methods . In addition to enabling the production of NNS components, colloidal processing allows for the introduction of small and well dispersed amounts of ceramic particles to anchor the grain boundary and to prevent their growth (pinning effect).…”

Corrosion and Tribocorrosion Behavior of Ti-Alumina Composites

“…Polyvinyl alcohol (PVA, Aldrich) was used as binder. Rheological studies were made to adjust the solid content of the suspensions to reach the optimum viscosity values for spray-dry; the details can be found in previous studies [18]. The slurries were spray-dried using Labplant SD-05 equipment (UK).…”