Microstructural evolution and resulting properties of differently sintered and heat-treated binder-jet 3D-printed Stellite 6

Stellite 6 components are manufactured from gas-atomized powder using binder-jet 3D-printing (BJ3DP) followed by curing and sintering steps for densification. Green parts are sintered at temperatures ranging from 1260 degrees C to 1310 degrees C for 1 h. Microstructural evolution and phase formation during sintering and aging are studied by optical and scanning electron microscopy, elemental analysis and X-ray diffraction. It was found that solidstate sintering was present at temperatures below 1280 degrees C with Cr-rich carbides present within grains; while supersolidus liquid phase sintering was the dominant sintering mechanism during sintering at 1290 degrees C and higher in which the Co-rich solid solution regions are surrounded by eutectic carbides. Sintering at 1300 degrees C resulted in the maximum density of similar to 99.8%, mean grain size of similar to 98 +/- 6 mu m with an average hardness of 307 +/- 15 HV0.1 and 484 +/- 30 HV0.1 within grain and at the boundaries, respectively. Aging was performed at 900 degrees C for 10 h leading to the martensitic transformation (fcc -> hcp) as well as an increase in eutectic carbides at boundaries and nano-sized carbides within grains where the average hardness within grains and boundaries was enhanced to 322 +/- 29 HV0.1 and 491 +/- 58 HV0.1, respectively. Fibroblasts seeded on top of 3D-printed Stellite 6 discs displayed a cell viability of 98.8% +/- 0.2% after 48 h, which confirmed that these materials are noncytotoxic. Presented results demonstrate that binder jetting can produce mechanically sound complex-shaped structures as shown here on a denture metal framework and small-scale knee model.