(Hf, Zr, Ta)O₂ oxide whisker reinforced TiZrTaHfNb /Ti–28Ni /ZrO₂ brazed joints by in-situ reaction: Microstructure and mechanical properties

The realization of brazing between the TiZrTaHfNb refractory high-entropy alloy (RHEA) and zirconia (ZrO₂) ceramic is of great importance in expanding the application of metal-ceramic composite parts. In this study, reliable brazed joints were achieved using a Ti–28Ni eutectic filler. The typical interfacial microstructure and the effect of brazing temperature on the microstructure and mechanical properties were thoroughly discussed. The results indicated the formation of complex oxides on the ZrO₂ ceramic side, including Ti₂O, Ni₂Ti₄O and (Hf, Ta, Zr)O₂. Additionally, the RHEA substrate near the brazing seam underwent a transformation from a single BCC phase to double BCC phases, which included a TaNb-rich BCC-1 phase and a Zr-rich BCC-2 phase. The formation of the double BCC phases was caused by the spinodal decomposition. As the brazing temperature rose, the thickness of the oxides layer slightly increased and the double BCC phases formed from the beginning and progressively coarsened. The maximum room shear strength was 124.1 MPa when the joint was obtained at 1040 °C for 10 min. The alternating distribution interlocking structure between MO₂ whiskers and Ni₂Ti₄O by in-situ reaction played a vital role in enhancing the interface strength.