Spark Sintering of TiB2 Reinforced Fe Matrix Composites with Both High Thermal Conductivity and Hardness, and Their Microstructural Characterizations

Abstract

TiB2 reinforced Fe matrix composites were investigated for their potential as a new generation of hot work tools which are mainly characterized by high thermal conductivity and high hardness in comparison with conventional materials. In this work, Fe30 vol%TiB2 composites were sintered at 1373K for different holding times (0, 0.3, 0.6, 1.8 and 3.6 ks). Apart from Fe and TiB2, newly formed phases of Fe2B and TiC were found in all sintered compacts. A good Fe/TiB2 interfacial cohesion was confirmed at atomic level at 0 ks, which was due to the occurrence of the special orientation relationship between {110} planes of Fe and {1010} planes of TiB2. The observation of dislocations in TiB2 particles, attributed to the activation of slip systems, showed the plastic deformation ability of TiB2 at high temperature. The reaction between Fe and TiB2 was due to TiB2 dissolution in Fe at 1373K and different diffusion depth of B and Ti atoms in Fe. Consequently, B directly reacted with Fe, since the solubility of B atoms was low in both α-Fe and γ-Fe. TiC probably precipitated from FeTiC solid solution along Fe grain boundaries in the cooling stage after sparking sintering, leading to a layer of Fe wrapping around TiB2. Among all the compacts, the one sintered at 1373K for 0.6 ks displayed the excellent properties which were comparable in Vickers hardness and 133% higher in thermal conductivity, compared with that of SKD61 as the commonly used practical material. This work provides a new perspective to fabricate a future generation of hot work tools.