Metal Fused Filament Fabrication (MF3) of CoCrMo Feedstocks

CoCrMo is one of the most important metal alloys for the fabrication of medical implants. The classic implant fabrication method is casting; in recent years, selective laser or electron beam melting as additive manufacturing methods have been established. Both methods mainly deliver parts with an anisotropic texture, which may not be advantageous for a lot of applications. In addition, both techniques are cost-intensive. In this work, the feasibility of the process chain of metal fused filament fabrication (MF3), covering the individual steps of compounding, printing, debinding and sintering, was investigated. Of particular importance is the feedstock composition consisting of suitable CoCrMo powder with a solid load of 60 Vol%, polyethylene glycol (PEG) and polymethylmethacrylate (PMMA) as binder components. Furthermore, acetyltributylcitrate (ATBC) was used as the plasticizer, necessary for a flexible filament, which can be wound on a spool. The influence of the ATBC content on compounding, feedstock melt viscosity and printing behavior was investigated. Samples of different sizes, like cuboids and tensile test specimens were debound and sintered to CoCrMo parts. A significant influence from the final sinter temperature on the part’s appearance and density was observed. Sintering at 1350 °C resulted in parts with a maximum relative density of almost 95% while retaining the shape of the green bodies. The slight increase to 1400 °C caused a partial sample melting with structural deformations visible at the edges, corners and at the surface. However, a density better than 99% could be reached. The measured ultimate tensile strength is lower than the reference value achieved with investment casting, but the elongation at break is equal or even higher. Nevertheless, the principal feasibility of the MF3 process chain for the realization of CoCrMo components could be demonstrated successfully.