Comparison of armor ceramics made by spark plasma sintering (SPS) and pressureless sintering

Armor ceramics are traditionally manufactured by processes such as hot pressing, pressureless sintering, and reaction bonding. These processes produce microstructures with grain sizes in the 5-100 μm range. More recently, processes such as microwave-assisted sintering and spark plasma sintering (SPS - also called field assisted sintering technology - FAST) have been introduced. Due to the non-conventional process-heat generation mechanisms, these processes achieve very high heating rates and significantly reduced process times. As a result, potential exists for achieving a much finer microstructure. This work assessed the possibility of achieving ultrafine-grained ceramics by SPS. Armor ceramics such as silicon carbide (SiC), boron carbide (B₄C), and their mixtures were produced by SPS as well as conventional sintering using identical starting powders. The parameters in both processes were systematically varied to assess their effects on microstructures and properties. Microstructures and properties of resultant materials were characterized. Process temperatures required for full densification (>98%) were reduced by 200-400°C using SPS and finer grained materials were indeed produced. Within the grain size ranges produced, a significant change in mechanical properties was not seen. Several problems were identified and overcome for scaling up the process to make 100 mm x 100 mm tiles with uniform, fine microstructure. Finally, the process was successfully scaled up to make 200 mm diameter B ₄C disks.