An oxygen-resistant refractory high-entropy alloy is synthesized in microlattice or bulk form by 3D ink-extrusion printing, interdiffusion, and silicide coating. Additive manufacturing of equiatomic HfNbTaTiZr is implemented by extruding inks containing hydride powders, de-binding under H2 , and sintering under vacuum. The sequential decomposition of hydride powders (HfH2 +NbH+TaH0.5 +TiH2 +ZrH2 ) is followed by in situ X-ray diffraction. Upon sintering at 1400 °C for 18 h, a nearly fully densified, equiatomic HfNbTaTiZr alloy is synthesized; on slow cooling, both α-HCP and β-BCC phases are formed, but on quenching, a metastable single β-BCC phase is obtained. Printed and sintered HfNbTaTiZr alloys with ≈1 wt.% O shows excellent mechanical properties at high temperatures. Oxidation resistance is achieved by silicide coating via pack cementation. A small-size lattice-core sandwich is fabricated and tested with high-temperature flames to demonstrate the versatility of this sequential approach (printing, sintering, and siliconizing) for high-temperature, high-stress applications of refractory high-entropy alloys.
Keywords: additive manufacturing; direct ink writing; oxidation; refractory high-entropy alloy; silicide coating.
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