Stainless steel 316L–hydroxyapatite composite via powder injection moulding: rheological and mechanical properties characterisation M. I. Ramli *1 , A. B. Sulong 1 , N. Muhamad 1 , A. Muchtar 1 and A. Arifin 1,2 Powder injection moulding is a manufacturing process capable of producing complex, precise and net-shaped components from metal or ceramic powders at a competitive cost. This study investigated the rheological properties of stainless steel 316L–hydroxyapatite composite by using palm stearin and polyethylene as a binder system, evaluates the physical and mechanical properties, and composition change of the sintered part at different temperatures through powder injection moulding process. Stainless steel 316L powder was mixed with hydroxyapatite by adding a binder system (palm stearin and polyethylene) at 58·0 vol% powder loading prepared via critical powder volume percentage. A green dumbbell-shaped part was produced via plunger-type injection moulding. The green part was sintered at 1000, 1100, 1200 and 1300°C at 3 hours. The value of flow behaviour index n is from 0·1 to 0·39, which is within range of the injectability index. The obtained activation energy is 5·75 kJ mol -1 . Morphological results indicate the formation of pores at a sintering temperature of 1000°C, a decrease of pores when the temperature is increased, and the occurrence of densification. At 1300°C it showed the highest mechanical properties of Young’s modulus which is 41·18 GPa. The decomposition of hydroxyapatite into β-tricalcium phosphate and tetracalcium phosphate phases started to occur at 1000 and 1100°C, respectively. The highest sintered density is 3·7744 g cm -3 which is close to the density of hydroxyapatite but the mechanical properties is higher than pure hydroxyapatite. Keywords: Powder injection moulding, Hydroxyapatite–stainless steel 316L composite, Rheological properties, Physical properties Introduction Powder injection moulding (PIM) is a technological process used to manufacture metal and ceramic and can produce small, complex, precise and net-shaped com- ponents at a competitive cost. 1 Powder injection mould- ing consists of four main steps, namely mixing, injection moulding, debinding and sintering. Hydroxyapatite (HA) is a calcium phosphate ceramic whose structure and composition are similar to that of human bones and teeth. 2,3 Hydroxyapatite is widely used as a bone substitute and dental implant because of its good properties, such as high biocompatibility, osseo- conductivity and bioaffinity with living tissues. 2,4,5 However, HA has low mechanical properties, such as brittleness and low fracture toughness, which limit its use in load-bearing applications. 6 Therefore, metallic materials are used to improve the mechanical properties of metal–ceramic composites. Stainless steel 316L (SS 316L), cobalt–chromium alloys (Co–Cr–Mo), titanium (Ti) and titanium alloys (Ti–6Al–4 V) are metallic materials that are widely used as implant materials, especially in the fields of orthopae- dics and dentistry. 7,8 These materials are used because of their good mechanical properties, corrosion resistance and the formation of an inert biocompatible oxide layer on their surface. As one of the medical grade metals used in implants, SS 316L is a well-known alloy that is suitable for use in internal fixation devices. 9 Stainless steel 316L is traditionally used because it is low cost, easy to fabricate and possesses high mechanical proper- ties. Properties such as corrosion resistance, biocompat- ibility, high tensile strength and fatigue resistance make SS 316L suitable as a surgical implant material. 10 The combination of the excellent strength properties of SS 316L and the bioceramics of HA can be used in load- bearing applications and bioactive composites. 11 1 Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Bangi, Selangor, Malaysia 2 Department of Mechanical Engineering, Sriwijaya University, 30662 Indralaya, Sumatera Selatan, Indonesia *Corresponding author, email mohdikram151@gmail.com © W. S. Maney & Son Ltd 2014 DOI 10.1179/1432891714Z.000000000938 Materials Research Innovations 2014 VOL 18 SUPPL 6 S6-100