Synthesis of TiB2/TiC/Al2O3 and ZrB2/ZrC/Al2O3 Composites by Low-Exotherm Thermitic Combustion with PTFE Activation

Abstract

TiB2–TiC–Al2O3 and ZrB2–ZrC–Al2O3 composites were produced via PTFE (polytetrafluoroethene)-activated combustion synthesis involving low-exotherm thermites. The reactant stoichiometries were 3TiO2 + 4Al + 0.5B4C + (1 − x)C + xCPTFE and 3ZrO2 + 4Al + 0.5B4C + (1 − y)C + yCPTFE. PTFE played a dual role in promoting the reaction and carburizing reduced Ti and Zr. The threshold amount of PTFE for the TiO2/Al-based reaction was 2 wt% (i.e., x = 0.15) and for the ZrO2/Al-based reaction was 3 wt% (i.e., y = 0.25). The increase in PTFE increased the combustion front velocity and reaction temperature. The TiO2/Al-based reaction was more exothermic than the ZrO2/Al-based reaction and exhibited a faster combustion front and a lower activation energy. The TiB2–TiC–Al2O3 composite was produced with the minimum amount of PTFE at x = 0.15. The formation of ZrB2–ZrC–Al2O3 composites required more PTFE at y = 0.5 to improve the reduction of ZrO2. Both triplex composites displayed mixed microstructures consisting of short-rod borides, fine spherical carbides, and Al2O3 agglomerates.