Duplex stainless steel self-ligating orthodontic brackets by micro-powder injection moulding

This work deals with the production of duplex stainless steel dental brackets by micro-powder injection moulding employing a thermoplastic binder based on high density polyethylene and paraffin wax. The starting powder was a mixture of ferritic and austenitic gas-atomized powders in a volume ratio of 50/50. Feedstocks with powder loadings of 50, 60, 65 and 68 vol.% were prepared. All feedstock compositions presented a pseudoplastic flow behaviour. The critical powder volume concentration experimentally determined through oil absorption method and applying a rheological model was 71 vol.%. A mixture with a 65 vol.% of solid loading was chosen to perform the complete route. Injection moulding stage was successfully carried out and green parts were obtained with an accurate dimensional precision. Green brackets were thermally debound under a cycle developed on the basis of thermogravimetric analysis. The cycle took place under argon atmosphere to prevent the oxidation of metallic powder and it lasted only 4 hours. Samples were successfully sintered in low vacuum at 1250ºC, final parts reached densities close to 98%. Scanning electron micrographs revealed a biphasic microstructure distinctive of duplex stainless steels.

Duplex stainless steel self-ligating orthodontic brackets by micro-powder injection moulding Articles