Fig. 1.

Creating CoCrFeNi high-entropy alloys via 3D ink-extrusion, reduction and sintering of oxide powder blends. a TGA mass loss of a loose blend of Co₃O₄ + Cr₂O₃ + Fe₂O₃ + NiO as function of temperature in a H₂ atmosphere. Initial reduction of Co₃O₄, Fe₂O₃ and NiO (blue shading) is followed by reduction of Cr₂O₃ (green shading). Inset: Same data as function of time, showing ramp and 1 h hold at 1557 K, when continuous mass loss occurs due to ongoing reduction of Cr₂O₃ until it is fully consumed. b Scanning electron micrograph of the blended oxide powder prior to TGA, showing agglomerate sizes <10 μm and sub-micron particle size. Scale bars are 5 µm and 1 µm (inset). c Combined 2D diffractograms of blended oxide prior (left) and after (right) the TGA measurement in H₂ showing the complete disappearance of all oxide-related diffraction intensities and formation of a face-centered cubic CoCrFeNi HEA. Scale bar is 20 nm^–1. d The two-step processing route first shapes the mill-mixed ink using 3D ink-extrusion into the desired architecture (a micro-lattice with 200 µm diameter struts, in the present example). In a second step, the powders in the green body are co-reduced, inter-diffused and sintered to yield a CoCrFeNi HEA micro-lattice with much smaller overall dimensions and strut diameter, without warping or cracking. Scale bars are 3 mm