Search

The micro-scale joining of two different materials using two-component micro-powder injection molding (2C-µPIM) is an intriguing technique. The formation of defects in bi-materials at different processing stages makes this technique challenging. This study presents the fabrication of defect-free bi-material micro-parts containing hydroxyapatite (HA) and 3 mol% yttria-stabilized zirconia (3YSZ) via 2C-µPIM. Critical powder volume concentrations (CPVCs) of 61.7 vol% and 47.1 vol% were obtained for the HA and 3YSZ powders, respectively. Based on the CPVCs, the optimal loadings for the HA and 3YSZ powders were selected as 60 vol% and 45 vol%, respectively. The HA and 3YSZ feedstocks were prepared by separately mixing the optimal powder contents with low-density polyethylene (LDPE) and palm stearin binders. The feedstocks displayed pseudoplastic behavior, and the lowest ranges of viscosity for the HA and 3YSZ at a temperature of 180 °C were 157.1–1392.5 Pa·s and 726.2–985.5 Pa·s, respectively. The feedstocks were injected to produce green HA/3YSZ micro-sized components. It was found that a solvent debinding temperature of 70 °C removed 60.6% of the palm stearin binder from the sample. In the thermal debinding stage, the open channels that formed in the bi-material sample's solvent debound at 70 °C and contributed to the removal of 93 to 95% of the binder system. When the debound bi-materials were sintered at 1300 °C, the highest relative density of 96.3% was obtained. The sintering operation revealed a linear shrinkage between 13 and 17% in the sintered HA/3YSZ micro-parts. [ABSTRACT FROM AUTHOR]

Metal-ceramic composites such as titanium-hydroxyapatite have been extensively studied as a new generation of implant material in medical application. The powder injection moulding (PIM) process is one the viable processing method in producing the titanium-hydroxyapatite composite which offers extreme geometry part at a lower cost of production. The final powder injection moulding (PIM) product was influenced by the feedstock rheological and thermal properties that related to the binder selection and the critical solids loading. The emphasis of this study was towards the rheological and thermal properties of Ti6Al4V-hydroxyapatite composite feedstock with the powder space holder using a low-density polyethene and palm stearin binder system. The critical solids loading for 90:10 of Ti6Al4V-hydroxyapatite with 20% of the space holder was selected for capillary rheometer tests. The solids loading was obtained at 73 vol.% with optimal solids loading in the range of 2–5% below the critical solids loading which were 68, 69 and 70 vol.%. All feedstocks exhibited shear thinning behaviour, with the shear rate and viscosity values in the range of the PIM feedstock. The work in this study found that the feedstock of 68 vol.% solids loading possessed the best rheological properties with a higher flow behaviour index. [ABSTRACT FROM AUTHOR]

The combination of metallic bio-inert material, stainless-steel 316L (SS316L) and a bio-active material, hydroxyapatite (HA) can produce a composite which has superior properties for orthopaedic applications. The main objective of this study is to investigate the effects of sintering temperature and holding time on the physical and mechanical properties of the sintered part. 50wt.% SS316L and 50wt.% HA were mixed with a binder system of palm stearin (PS) and polyethylene (PE) at 61 vol.% powder loading. Rheological properties show a pseudo-plastic behaviour of the feedstock, where viscosity decreases with increasing shear rate. The feedstock was injection moulded into a tensile bar shape while thermal debinding was carried out at 320°C and 500°C. The brown parts were sintered at 1000, 1100, 1200 and 1300°C, with three different sintering times of 1, 3 and 5 hours in the furnace. It was found that the highest sintered density measured was 95.61% of the theoretical density. In addition, the highest hardness and Young’s modulus measured were 150.45 HV and 52.61 GPa respectively, which are higher than those of human bone. The lowest percentage of carbon content was 0.022wt.% given by the sample sintered at 1300°C for 1 hour. Therefore, SS316L/HA composite with good mechanical and physical properties was successfully produced through the PIM process. [ABSTRACT FROM AUTHOR]

This review presents a thorough survey of academic work on the analysis and application of the usage of nano-sized powders in powder injection molding (PIM). The PIM process has become well-established in the fabrication of micro parts or microstructured parts in recent years. Given their unique inherent properties, nano-sized powders are widely used over micro-sized powders in all high-volume PIM methods of fabricating metal and ceramic components. Current critical issues are discussed, such as the effect of nano-sized powders on the mixing, injection, debinding, and sintering processes, as well as the effects on the feedstock and final properties of the components. Based on this survey, the current study proposes improvement on the limitations caused by applying nano-sized powders in the PIM process by utilizing new binder systems, milling, new deagglomeration methods, and new sintering procedures. Fields and topics that require further research are identified, and prospects for future industrial implementation of the process are given. This study is the first to aims at providing insights into the effects of using nano-sized powders in the PIM process. Moreover, this paper shows the great potential for further investigations and innovation in the field of powder injection molding using nano-sized powders. [ABSTRACT FROM AUTHOR]