Design of a double-layer composite ceramic and its brazing with niobium

Abstract

A double-layer composite ceramic incorporating excellent mechanical and joining properties was designed by optimizing the composition of the TiB2–TiC–SiC ceramic. First, the ceramic composition that optimized the mechanical properties was explored by fabricating TiB2–TiC–SiC ceramics with four different compositions. The results showed that the flexural strength of the composite ceramics increased with the increase of TiC component in the composite ceramics, albeit with a slight decrease in fracture toughness. The TiB2–20TiC–20SiC (vol. %) ceramic exhibited excellent mechanical properties with a hardness of 20.6 GPa, fracture toughness of 6.21 MPa ·m1/2, and flexural strength of 486 MPa. Then, the four TiB2–TiC–SiC composite ceramics were brazed with Nb to investigate the ceramic composition that optimized the joining performance. As the TiC component in the composite ceramics increased, the reduction of the Nb3B2 phase and the increment of the (Ti, Nb)2Ni phase within the reaction zone along the ceramic side can be noticed, and the width of this reaction zone decreased from 29 μm to 15 μm. The TiB2–5TiC–20SiC (vol. %) ceramic demonstrated promising joining performance with a maximum shear strength of 229 MPa for its brazed joint with Nb. Finally, a double-layer composite ceramic with the surface composition of TiB2–5TiC–20SiC and base composition of TiB2–20TiC–20SiC was prepared. The maximum shear strength of 248 MPa was achieved by brazing the double-layer composite ceramic with Nb at a temperature of 1433 K for 10 min, representing a 39 % improvement over the unoptimized condition.