Fabrication of zirconia-toughened alumina parts by powder injection molding process: Optimized processing parameters

Zirconia-toughened alumina (ZTA) parts were fabricated by using a powder injection molding process that utilizes a multi-component binder system based on high-density polyethylene, paraffin wax, and stearic acid. The entire aspect of the manufacturing process, which includes mixing, injection molding, debinding, and sintering, were optimized in this study. ZTA powder was mixed with binders at powder loading ranging from 53 vol% to 59 vol%. The optimum powder loading was determined by analyzing the rheological properties and homogeneity of feedstocks. During injection molding, the temperature and injection pressure parameters were manipulated to obtain optimum density results. A two-stage debinding process (solvent and thermal) was used to remove binders in green parts. Debound parts were sintered at temperatures ranging from 1400 °C to 1600 °C for 2 h. The shrinkage, density, and hardness of the sintered parts were measured. Results show that with homogeneous mixing, the feedstocks were transformed into pseudoplastic in less than 30 min. Powder loading of 57 vol% is the most optimal case for injection molding according to the power law index and flow activation energy values. The theoretical relative density reached 90.27% with defect-free parts under optimum injection temperature and pressure. The weights of the parts decreased by 82.26% during solvent debinding at 60 °C, whereas the binders were completely degraded at approximately 550 °C during thermal debinding. Experimental results also indicate that the shrinkage, density, and hardness reached their maximum values at a sintering temperature of 1600 °C. The sintered parts were densified with approximately 98% theoretical density, hardness of 1582.4 HV, and 15% shrinkage value.