Chapter 7. Effect of Microstructure and Mechanical Properties on the Ballistic Performance of SiC-Based Ceramics

Summary

Processing additives and conditions allow a wide variation in microstructures and mechanical properties for SiC-based ceramics prepared by hot pressing. Five experimental materials with a wide variety of microstructures and mechanical properties were fabricated and compared with SiC-N, a commercially available material. Quasi-static fracture modes varied from predominantly transgranular to primarily intergranular, leading to a twofold increase in the single-edged precracked beam (SEPB) fracture toughness. Hardness varied due to an order of magnitude change in grain size, while porosity varied by less than one percent. Ballistic V50 performance was measured using 14.5 mm projectiles shot at ceramic/composite targets. The relative ranking of ballistic performance is discussed in terms of microstructure and mechanical properties.

The data indicate that a wide variety of SiC-based materials can give good ballistic results, contradicting some of the theories about what is important to improve ceramics for armor. Several materials were as good or better than SiC-N in these tests. The relative ballistic ranking was not predictable based solely on hardness, toughness, strength, grain size, elastic modulus, or fracture mode. Although Weibull modulus correlated with ballistic performance, this is likely coincidental since strength values extrapolated to a low failure probability based on the respective Weibull distributions could not rank the ballistic results.