Application of thermal analysis in the selection of polymer components used as a binder for metal injection moulding of Co–Cr–Mo alloy powder

Abstract

To produce the polymer-powder slurry for injection moulding the thermoplastic polymers such as polypropylene, high-density polyethylene and ethylene-vinyl acetate were used. Depending on skeletal polymers, in every feedstock paraffin wax (PW) was used in the amount of 50% of binder. Application of PW gives the possibility using solvent debinding or thermal debinding at a lower temperature. Then the open porosity into the injected samples reduces the time of thermal debinding of binder residue. Application of one type of skeletal polymer requires using a long isothermal step. The use of a blend of skeletal polymers enables subsequent thermal degradation which consecutively removes skeletal polymers during the heating to the sintering temperature, to minimise the time of isothermal stops. The rheological properties of blends used as a binder and next feedstocks were investigated during mixing in the twin-screw extruder and capillary rheometer. This results gives the information about the possibility to produce feedstocks and then to their injection moulding. Thermal behaviour of samples was determined by differential scanning calorimetry and thermogravimetric analysis to obtain the information about the temperature of mixing the polymers and to propose the thermal debinding cycle.