Synthesis of TiN-TiB2-hBN composite powders with a core-shell structure and preparation of bulk samples

TiN-TiB2-hBN composite powders were synthesized by a nitride boronizing process using TiN and amorphous boron as the raw materials, and the reaction process of TiN-B powder mixture was investigated by heat treatment at elevated temperatures. At 1400 degrees C in a vacuum, TiN-TiB2-hBN composite powders with a core-shell structure of layered hBN-wrapped TiB2 were obtained, which can be used to prepare ceramic composites with excellent properties. The results showed that B atoms began to diffuse into TiN and replace the N atoms to form TiB2 at high temperature; then, the substituted N escaped outwards, and upon contacted with B, formed hBN at the surface of the TiB2 particles. The relative density, bending strength, and fracture toughness of the 70 vol% TiN-17.6 vol% TiB2-12.4 vol% hBN (TB73) composite prepared by reactive sintering were 98.90%, 521 MPa, and 4.22 MPa m(1/2), respectively, which were much higher than that of fabricated via conventional method (TBN73: 88.02%, 198 MPa, and 2.58 MPa m(1/2)).