Preparing MIM Feedstocks for Bio-Applications Using an Agar-Based Binder

The present study aims to prepare feedstocks for MIM (Metal Injection Molding) where the metal powders are 316L stainless steel powders (SS). The master objective is to compare the performance of a biodegradable binder with a commercial one based on polyolefins. Different challenges must be overcome in SS injection molding, as follows: to decrease binder/carbon content in feedstocks; to decrease carbon contamination during debinding and sintering; to avoid the formation of chromium carbide and presence of precipitation-free zones; to avoid the grain growth during sintering and to reduce the feedstock price. The optimization of the feedstocks was performed using a torque rheometry technique. Feedstocks of coated and uncoated SS powders mixed with an agar-based binder were used to produce sound parts. A feedstock constituted by SS powders mixed with a high quality commercial binder was the standard. SS with agar-based on feedstocks can admit solids content similar to those based on the commercial binder (62 vol.%). For similar powder content, the sinters resulting from feedstocks with the agar-based binder shows a lower quantity of solid solution of carbon and chromium carbides, absence of precipitation-free zones than commercial feedstocks and good sinter soundness. Coating powders with nanocrystalline stainless steel contribute to control grain growth during debinding and sintering.