Alumina-titanium diboride in situ composite by self-propagating high-temperature synthesis (SHS) dynamic compaction: Effect of compaction pressure during synthesis

This manuscript investigates the effect of compact pressure during in situ synthesis of Al2O3-TiB2 composite by self-propagating high-temperature synthesis (SHS) process on microstructure, toughness, hardness and modulus. The oxidation behaviour of the composite was also studied. The porosity was found to decrease with the increase in dynamic compaction pressure and grains became finer forming a nano-composite with very fine boride grains in alumina matrix. The densification was mostly complete at 13 MPa about 95%-96% densification, and it remained similar at higher loads up to 18 MPa. Microhardness increased with compaction pressure, and a maximum average hardness of 3536 Hv was obtained for sample compacted at 18 MPa pressure. Hardness and modulus under dynamic indentation did not show clear trend of increase with compaction pressure as in microhardness. The average hardness of 22.684 GPa and a mean modulus of 360.904 GPa was measured for 13 MPa compacted sample. Fracture toughness was found to increase with compaction pressure. Oxidation studies showed stability against oxidation up to 900 °C, and no significant changes in properties were observed. It was observed that during the SHS dynamic synthesis of Al2O3-TiB2 composite, the compacting pressure had lot effect on microstructure, hardness, modulus and densification. A high hardness with reasonable toughness and oxidation resistant up to 900 °C temperature has been achieved in Al2O3-TiB2 composite.