Investigation of vacuum active brazing of (HfZrTiTaNb)C high-entropy carbide ceramic to Nb with TiZrCuNi filler alloy

Abstract

Good metallurgical joining was carried out between (HfZrTiTaNb)C high-entropy carbide and Nb via 37.5Ti37.5Zr15Cu10Ni (wt.%) filler alloy. The microstructure of the joint was (HfZrTiTaNb)C/(Zr, Ti)C/α-Ti + β-Ti + (Zr, Ti)2(Cu, Ni)/Zr(s, s) + β(Ti, Nb) + Nb(s, s)/Nb. The generation of (Zr, Ti)C and β(Ti, Nb)+Nb(s, s) phases between the liquid phase and ceramic and Nb were vital to realize the joining. The constituent phases of the joint did not change with the variation of brazing process parameters. When the brazing temperature rose from 920 to 1000 °C, the thickness of the (Zr, Ti)C reaction layer increased by 0.2 μm, while it remained roughly unchanged as the holding time was extended from 1 to 30 min. This unusual interfacial evolution pattern could partially attribute to the unique properties of sluggish diffusion and severe lattice distortion of the high-entropy ceramic. With the increase of brazing process parameters, the shear strength of the joints showed a mountain peak characteristic of increasing and then decreasing, and the maximum value of 154 MPa was obtained at 960 °C for 5 min. The fracture took place in the brittle (Zr, Ti)2(Cu, Ni) phase, and then passed through the (Zr, Ti)C phase and the ceramic substrate.