Abstract
Transparent armours are conventionally fabricated with glass, a relatively low-strength material. High thicknesses are thus required to inhibit ballistic threats, which results in a design ordeal of increased weight. Transparent ceramics are increasingly gaining traction as potential substitutes for the structurally inadequate glass products. Polycrystalline MgAl2O4-spinel is one such an advanced ceramic being studied and developed for this application. Spark Plasma Sintering (SPS) is a relatively novel fabrication route that has demonstrated great progress in achieving transparent ceramics. In this work, dense spinel parts were synthesized from Al2O3 and MgO starting powders, with varying boric acid (H3BO3) additions. A two-step heating and pressing profile was utilized to accommodate the volumetric expansion that comes with spinel formation. The influence of varying H3BO3 additions in the system was observed through SPS data, XRD and density measurements. Then the transparent MgAl2O4 spinel parts were fabricated through spark plasma sintering using H3BO3 (0.5wt%) or LiF (1wt%) sintering additives. The sintering parameter that produced appealing transparent parts was achieved at 1600⁰C and 1650⁰C for two hours and three hours holding time. The Archimedes method was used to measure the average densities of the sintered components. The sintered components were characterized using XRD for possible phase transformations during sintering, an inverted light microscope was used for microstructural analysis. A Vickers indenter was used to evaluate the hardness and fracture toughness of the sintered compacts. The results showed that boric acid was found to offer the best densification and mechanical properties but rendering the components susceptible to carbon contamination from the graphite tooling of the SPS. The LiF-doped parts exhibit exceptional in-line transmittance results, and these parts virtually have no carbon contamination observed. Transparent spinel parts, with their superior mechanical properties, prove to be potential substitutes for the traditional bulletproof glass.