Abstract
Aqueous suspensions of zirconium diboride (ZrB 2 ), boron carbide (B 4 C) and tungsten carbide (WC) with dispersant and water-soluble polyvinylpyrrolidone (PVP) were investigated for processing by room-temperature injection molding, a novel, environmentally benign ceramic processing method. B 4 C and WC were used as sintering aids, and the as-received powders were attrition milled to reduce particle size to promote full densification of ZrB 2 specimens by pressureless sintering. Zeta potential measurements of individual ZrB 2 , B 4 C and WC powders and of powder mixtures revealed that maximum stability was achieved in aqueous solutions of attrition milled powder mixtures dispersed using an ammonium polyacrylate dispersant. A maximum powder loading of 49 vol% with ≤5 vol% PVP was attained for ZrB 2 /B 4 C/WC suspensions with dispersant. Although exhibiting a time-dependent rheological response determined by parallel-plate rheometry, suspensions containing 49 vol% powders and ≤3 vol% PVP, as well as suspensions of 46 vol% powders and ≤4 vol% PVP, were flowable under the conditions of the process. ZrB 2 rings prepared by room-temperature injection molding were machinable prior to binder removal and exhibited maximum brown densities of 56% true density (TD). Sintered densities were >98%TD with ~20% linear shrinkage. Scanning electron microscopy revealed an average grain size of 7.3±2.8 µm, and chemical analysis confirmed that no undesirable oxide phases remained in the sintered ZrB 2 specimens. Aqueous ZrB 2 -based suspensions containing B 4 C and WC sintering aids and PVP were effectively processed via room-temperature injection molding to yield dense ZrB 2 rings after binder burnout and pressureless sintering.
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