BAO Linyan, LIAO Zhixiong, ZHANG Jingjing, ZHANG Wei'en, Yaohong Chiou, XIAO Zhiyu
【Objective】 Zirconia ceramics are widely used in electronics, biomedical devices, and other fields due to their excellent mechanical properties, as well as good wear and corrosion resistance. However, their conventional fabrication processes still face challenges: traditional injection molding is limited by the low debinding efficiency of paraffin‑based binders, while the poor flowability of powders in conventional compression molding makes it difficult to form complex parts. Polyoxymethylene (POM)‑based binders exhibit superior comprehensive performance, enabling efficient debinding and reduced deformation, thus providing a new approach to solving ceramic forming issues. This study develops a POM‑based zirconia ceramic feedstock suitable for compression molding, and investigates feedstock preparation, process optimization, debinding, sintering, and application, aiming to provide an important technical basis for high‑quality industrial production of zirconia.
【Method】 Using 3 mol% Y₂O₃‑stabilized zirconia powder (3Y‑TZP) as the raw material, the 3Y‑TZP powder and a POM‑based binder were mixed at a volume ratio of 1∶1 in an internal mixer (180 ℃ for 2 h). The mixture was then mechanically crushed and sieved through a 60‑mesh screen to obtain fine‑particle feedstock with particle size ≤0.25 mm. Green compacts of dimensions 30 mm × 12 mm were formed by warm compression molding under different mold temperatures, holding times, and pressing pressures. The green compacts were subjected to catalytic debinding under different debinding media (oxalic acid, nitric acid debinding furnace), temperatures (110, 120, 130 ℃), and times (1, 3, 5, 7 h). The debound samples were sintered in a box furnace at sintering temperatures (1 400, 1 450, 1 500, 1 550, 1 600 ℃) and holding times (1, 2, 3, 4 h). The optimal process parameters for compression molding, catalytic debinding, and sintering were systematically investigated, and the microstructure and mechanical properties of the final zirconia products were characterized.
【Result】 Warm compression molding experiments of the POM‑based feedstock showed that the green density first increased and then decreased with increasing mold temperature, holding time, and pressing pressure. Under the conditions of mold temperature 180 ℃, holding time 10 min, and pressing pressure 80 MPa, the green density reached 3.51 g/cm3, with a dense and uniform cross‑section. Feedstock with a high binder content achieved high‑density zirconia ceramics during the sintering stage when warm‑compacted. In contrast, compression molding at room temperature could not yield high density after sintering. Catalytic debinding in a nitric acid atmosphere at 120 ℃ for 5 h resulted in almost complete removal of the POM binder from the green compacts. With increasing sintering temperature and holding time, grain size and volumetric shrinkage continuously increased, while relative density and mechanical properties first improved and then slightly decreased. Sintering at 1 500 ℃ for 2 h was identified as the optimal condition: the material exhibited t‑ZrO2 as the main phase, a uniform and dense microstructure with no obvious pores or defects, a relative density of 99.1%, Vickers hardness of 1 384.53HV, and flexural strength of 1 073.25 MPa.
【Conclusion】 This study employs warm compression molding of a POM‑based zirconia ceramic feedstock, overcoming the problems of insufficient powder flowability and difficulty in forming complex parts associated with conventional room‑temperature compression molding, and reveals the fundamental rules of forming and sintering. Furthermore, the developed warm compression molding process using the POM‑based binder for 3Y‑TZP provides a basis for low‑cost, high‑efficiency compression molding of high‑performance complex zirconia ceramics.
