3D ink extrusion and co-reduction of pre-alloyed powder, mixed elemental, or oxide or hydride blends allows to create alloys and intermetallics in situ upon thermal treatment. In case of alloys interdiffusion is required to homogenize the compositional differences, unless pre-alloyed powder is used. Such pre-alloyed powder is typically more expensive than elemental powders and limits compositional flexibility. For many alloy systems, the metallic constituents can be reduced or decomposed from compounds (such as oxides or hydrides) to access sub-micron powder sizes. In their metallic form such small powders tend to be oxidized and be difficult to handle, whereas oxides are fully stable in air. Using small powders greatly accelerates sintering kinetics and allows to fully densify the printed material.
Affordable Low Modulus Titanium Alloys
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High entropy alloy microlattices
Here, the used ink contains a blend of Co3O4+Cr2O3+Fe2O3+NiO that is reduced to metallic Co, Fe, Ni that interdiffuse and accept freshly reduced Cr to form an equiatomic CoCrFeNi high entropy alloy. This approach allows to create a wide range of (non-)equiatomic compositions without limitations on powder availability. Additionally, using fine oxide powders leads to small metal grains that further accelerate sintering. The resulting high entropy alloy microlattices have dense struts, but a controlled level of macroporosity, defined by their strut assembly. This allows to control the mechanical properties of the microlattice. Based on the good ductility of CoCrFeNi, the microlattices show excellent behavior at ambient and cryogenic temperatures.
- C. Kenel, N.P.M. Casati, D.C. Dunand, 3D ink-extrusion additive manufacturing of CoCrFeNi high-entropy alloy microlattices, Nature Communications 10 (2019) 904.
- Swiss National Science Foundation, Early Postdoc Mobility fellowship 2017-2018 under grant No. 172180