High-Performance Zirconia-Toughened Alumina Ceramics Fabricated by Injection Molding Combined with Hot Isostatic Pressing

With the increasingly demand of ceramic components in biomedical engineering, microelectronic packaging, and related fields, the requirements for ceramic geometric complexity, accuracy and mechanical properties become popular. Injection molding technology possesses distinct advantages of high dimensional accuracy, superior shape fidelity, and elevated production efficiency for the mass production of geometrically intricate ceramic parts. This study fabricated fine-grained zirconia-toughened alumina (ZTA) ceramics via submicron powder injection molding and hot isostatic pressing (HIP). Furthermore, the rheological behavior of the feedstocks, thermal debinding kinetics, microstructure, and mechanical properties were systematically investigated.

A ZTA powder with an average particle size of 0.281 μm was used. The binders used consisted of polypropylene (PP, 99% purity; same for subsequent materials), polyethylene (PE, 99%), polystyrene (PS, 99%), ethylene-vinyl acetate (EVA, 98%), paraffin wax (PW 99%), stearic acid (SA 99%) and dibutyl phthalate (DBP, 99.5%). The mass ratio of the binder components m(PP/PE/PS) : m(EVA) : m(PW) : m(SA) : m(DBP) in the feedstock was 30 : 30 : 30 : 5 : 5. The ceramic powder and organic binders were fully mixed by an internal mixer (Guangdong C Fine Technology Co., Ltd, China) at 180 ℃ for 90 min, then crushed into granules of less than 5 mm. The solid loading of the feedstocks was 54%, 56% and 58%, respectively. Injection molding was performed using a model VE600Ⅲ-80hs commercial injection molding machine (Zhafir Plastics Machinery GmbH., Germany). Thermal debinding was conducted using a hot air circulation furnace (Wanlong Electric Furnace Co., China). The green bodies were pre-sintered in a muffle furnace (Ruibang Intelligent Technology Co., China) and then HIP post-treated using a model AIP10-30H system (AIP Co., USA). The rheological properties of feedstocks were tested at 190 ℃ by a model Rosand RH2000 capillary rheometer (Malvern Co., UK). The thermal decomposition behavior of binders and green bodies within the temperature range of 30–600 ℃ was examined using a model STA-449C simultaneous thermal analyzer (NETZSCH Co., Germany) coupled with a model TENSOR Ⅱ FT-IR thermogravimetric-infrared spectroscope (BRUKER Co., USA). The microstructures of ZTA samples were analyzed by a model JSM-6700F field emission scanning electron microscope (SEM, JEOL Co., Japan). The hardness of the samples was measured using a model Instron Wilson VH1150 Vickers hardness tester (BRUKER Co., USA). The flexural strength of the samples was evaluated via the three-point bending method using a model PT-1176 universal testing machine (Baoda instrument Co., Ltd., China).

At 190 ℃, the shear viscosity of the raw material decreases with increasing shear rate, demonstrating the pronounced shear-thinning characteristics advantageous for injection molding. The feedstocks utilizing polypropylene as a skeletal binder exhibit a typical shear-thinning rheological behavior and a homogeneous microstructural morphology. At a shear rate of 100 s^–1, the shear viscosities of raw materials with solid contents of 54%, 56%, and 58% are 466.79 Pa·s, 900.90 Pa·s, and 2352.54 Pa·s, respectively. The non-Newtonian index reaches its minimum value (i.e., n=0.47) for the material at 56% solid-content. The TG and TG (DSC)-FTIR analyses reveals that the mixing process of binders does not affect the decomposition products, but affects the degradation process. The mixing of binders leads to an eutectic melting. Furthermore, a winding structure is formed between the straight chain part of DBP and other binder components due to a physical or chemical adsorption of binders on the surfaces of ceramic particles. Therefore, the initial degradation temperature increases. The ZTA ceramics with a high relative density of 98.81% and fine grains can be fabricated via air pre-sintering and HIP post-treatment technology. The ZTA ceramics pre-sintered at 1500 ℃ and HIP-ed at 1450 ℃ have superior comprehensive properties with a hardness of (21.73±0.42) GPa and a flexural strength of (656±24) MPa. Based on the optimized process, the fabricated ceramic capillary bonding tools exhibit excellent dimensional accuracy and superior surface finish.

In this work, fine-grained ZTA ceramics were fabricated via submicron powder injection molding combined with HIP. The feedstocks with polypropylene (PP) as a skeletal binder exhibited characteristic shear-thinning rheological behavior and homogeneous microstructure. At a solid content of 56%, the feedstocks demonstrated the minimum non-Newtonian index (n=0.47). During mixing, degradation products of the binder system remained stable, while preserving the mixing sequence, indicating partial processing compatibility among binder components. The ZTA ceramics pre-sintered at 1500 ℃ and HIP-ed at 1450 ℃ exhibited superior comprehensive properties (i.e., a relative density of 98.81% (4.15 g/cm³), hardness of (21.73±0.42) GPa, and flexural strength of (656±24) MPa). This study could realize the preparation of fine-grained, high-density ZTA ceramic capillary bonding tools, providing an effective pathway for manufacturing precision ceramic components with micro-scale structures.