Ink‐Extrusion 3D Printing and Silicide Coating of HfNbTaTiZr Refractory High‐Entropy Alloy for Extreme Temperature Applications

Abstract 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 H 2 , and sintering under vacuum. The sequential decomposition of hydride powders (HfH 2 +NbH+TaH 0.5 +TiH 2 +ZrH 2 ) 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.