Excellent high-temperature strength of (HfZrTiTaNb)C high-entropy carbide diffusion-bonded joint via in-situ alloying of Ni/Nb/Ni composite interlayer

To obtain high-entropy carbide (HEC) joints with excellent high-temperature performance, a (HfZrTiTaNb)C HEC joint featuring a direct diffusion-bonded interface with Nb-based interlayer was successfully fabricated at relatively low temperatures of 1150-1250 °C for 60 min under 10 MPa. Starting from a modified Ni/Nb/Ni composite interlayer with a Nb content of > 64 at.%, an alloyed Nb₂Ni layer was constructed in situ by accelerating the directional diffusion of Ni atoms from the high-entropy interface into the remaining pure Nb through the Ni-Nb eutectic liquid. Moreover, the excess liquid phase was squeezed out of the bonding region, ensuring the absence of Ni-based compounds. Leveraging the intrinsic interfacial stability and sluggish diffusion effect, the HEC with its original lattice structure was capable of developing diffusion bonding with the Nb₂Ni layer, instead of interacting with the liquid phase. The high reliability of the HEC/Nb₂Ni bonded interface was confirmed by the coherence of (13) _HEC // (141) _Nb2Ni and calculated lattice misfit of 0.044. The HEC joint had high room-temperature strength of 174 MPa due to a homogenous Nb₂Ni layer that exhibited nanohardness (15.2 ± 1.5 GPa) and elastic modulus (219.9 ± 17.5 GPa). Further, the strength of the HEC joint did not decrease at 1000 °C, enhancing ~ 49% over that of HEC/Ni/HEC diffusion-bonded joints with stringent requirements on surface flatness. This suggested the HEC/Nb₂Ni interface had excellent resistance to high-temperature softening, even though it was invariably the initial failure location. This work is informative for designing bonding structures and preparing HEC components.