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

Abstract

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\u202f°C to 1310\u202f°C for 1\u202fh. 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 solid-state sintering was present at temperatures below 1280\u202f°C with Cr-rich carbides present within grains; while supersolidus liquid phase sintering was the dominant sintering mechanism during sintering at 1290\u202f°C and higher in which the Co-rich solid solution regions are surrounded by eutectic carbides. Sintering at 1300\u202f°C resulted in the maximum density of ~99.8%, mean grain size of ~98\u202f±\u202f6\u202fμm with an average hardness of 307\u202f±\u202f15\u202fHV0.1 and 484\u202f±\u202f30\u202fHV0.1 within grain and at the boundaries, respectively. Aging was performed at 900\u202f°C for 10\u202fh leading to the martensitic transformation (fcc\u202f→\u202fhcp) 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\u202f±\u202f29\u202fHV0.1 and 491\u202f±\u202f58\u202fHV0.1, respectively. Fibroblasts seeded on top of 3D-printed Stellite 6 discs displayed a cell viability of 98.8%\u202f±\u202f0.2% after 48\u202fh, which confirmed that these materials are non-cytotoxic. 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.