Wettability and brazing of (MoNbTaVW)C High-Entropy Carbide by Ni and NiTa

This study aimed to design and validate a suitable brazing filler for the joining of (MoNbTaVW)C High-Entropy Carbides (HECs). CALPHAD calculations were used to analyse phase equilibria of ternary C–Ni-M (M: Mo, Ta, W) systems at 1480 °C and to select a suitable alloy composition for brazing. Wettability and high-temperature interactions with the HEC substrates were investigated using the sessile drop technique. While pure Ni provided a good wetting (≤15°) but an excessive dissolution, the Ni83Ta17 alloy exhibited a comparable wetting with a significantly reduced dissolution due to the formation of interfacial TaCx-rich phases. Consequently, the NiTa alloy was employed as a filler to braze HEC ceramics using a pressure-less field-assisted sintering technique (FAST) furnace at 1480 °C, resulting in a crack-free, homogeneous joint. The interfacial TaCx-rich phase exhibited a high nano-hardness (∼24 GPa) and indentation elastic modulus (∼311 GPa). Single-lap offset shear tests confirmed a very high strength of the joints (∼220 MPa), demonstrating the viability of the NiTa alloy for joining HEC.