Fabrication of Al 2O 3–ZrB 2 in situ composite by SHS dynamic compaction: A novel approach

Abstract

Al 2O 3–ZrB 2 in situ composites of 97% of theoretical density were successfully fabricated by a novel self-propagating high temperature synthesis (SHS) dynamic compaction, using less expensive raw materials zirconium oxide, boron oxide, and aluminium. The process is fast, energy efficient, where no furnace sintering is required. The process inhibits and controls the grain growth and microstructure. The densification behaviour and correlation with microstructure of the SHS dynamic compacts were compared with the furnace sintered composite samples where the composite powder was prepared by SHS process. The furnace sintered samples showed coarser grain growth and maximum density of 94.5% of theoretical density was achieved. The SHS dynamic compacted in situ composite had much finer grains in the range of 0.5–3 μm with density 95.5% of the theoretical value. The average grain size was found to decrease from 10 μm to 1.4 μm for alumina and from 5.4 μm to 1.0 μm for zirconium diboride from furnace sintering to SHS dynamic compaction, respectively. Addition of Al 2O 3 as a diluent during SHS reaction enhanced the density to 97%. During SHS dynamic compaction, the amount of liquid and the time interval at which the sample stays at high temperature are the controlling factor of the final microstructure and the densification of the composite.