Effect of nickel boride and boron additions on sintering characteristics of injection moulded 316L powder using water soluble binder system

A new metal injection moulding system for 316L stainless steels has success fully been derived and tested. A mixture of small water atomised powder (av erage size 15 mum), larger gas atomised powder (average size 75 mum), and s intering additives has been coupled with a new water soluble binder system for economical powder injection moulding. The details for each process step and the effect of sintering additives are described. The binder system con sists of poly (2-ethyl-2-oxazoline) as the leachable polymer, polyethylene as the backbone, and stearic acid as a surfactant and plasticiser. This bin der system provides satisfactory mixture stability, excellent mouldability, and reasonably fast water leaching and thermal debinding rates. The optimu m powder/binder compositions were determined using torque and capillary rhe ometry. Densification was by persistent liquid phase sintering through addi tives, such as nickel boride and boron. This 316L powder system was sintere d to 7(.)9 g cm(-3) (98(.)75% of theoretical) at 1285 degreesC using nickel boride addition and at 1245 degreesC using boron addition. nickel boride a dditions are particularly effective at increasing the tensile strength and ductility. In contrast, the boron additions only increase the tensile stren gth and decrease ductility. Based on microstructure evaluations, this effec t is traced to a continuous boride phase on the grain boundaries of the bor on doped samples and a discontinuous boride phase on the grain boundaries o f the nickel boride samples. (C) 2001 IoM Communications Ltd.