Hybrid Super Hard & Light Weight Layered Ceramic Tiles by Field Assisted Sintering Technology (FAST) for Vehicle

Project Summary: Significant progress has been made under the ONR funding towards the understanding of sintering phenomena of SiC and B4C ceramic tiles produced by emerging Field Assisted Sintering Technology (FAST). The research thrust was also focused towards: (i) evaluating the performance of B4C ceramic tiles using various evaluation matrices (including hardness, flexural strength, fracture toughness and ballistic testing and compare with the base line commercial materials); (ii) developing new architecture of B4C ceramic tiles, i.e., layered structure with improved ballistic performance over base line without sacrificing its density and hardness. Summary of the accomplishment as follows: (i) Mechanical properties including hardness, fracture toughness, flexural strength and ballistic testing of FAST B4C is comparable with commercial Hot Pressed B4C ceramic tiles provided by Coorstek. (ii) New architecture of B4C ceramic tiles, i.e., layered structure exhibited better performance in terms of impact energy absorption of projectile associated with crack deflection, preventing stress induced phase transformation from crystalline to amorphous in B4C ceramic tiles. (iii) Post analysis of the fragmented ceramic tiles after ballistic testing exhibited two important information: (a) layered laminated ceramic tiles did not show micro-cracks, and (b) cracks propagation often stopped at the interface indirectly indicative of energy absorption at the composite region. These observations need to be further amplified and confirmed by conducting multi hit ballistic testing on large sized ceramic tiles that will be conducted under this proposed research effort; (iv) Comparative manufacturing cost analysis of FAST vs HP shows that FAST is relatively more cost effective (50% shorter processing cycles and 40-60% less energy consumption)- assuming having approximately same working volume and throughput. According to the armor community, the hallmarks of a good armor system are the low cost, low density, high hardness and good fracture toughness. B4C is one of the hardest known materials, ranked third behind diamond and cubic boron nitride. However, B4C material has poor fracture toughness. Fracture toughness of B4C could be increased by making composite structure that is part of this research proposal as summarized below. Hardness and fracture toughness of B4C is a very critical requirement that can be increased by making composite structure. Preliminary investigation shows that hardness of the B4C could be further increased from VHN 3200 to VHN 4000 (16% improvement) by incorporating 10% Cr2C3. Hardness can be further improved to VHN 7000-8000 (200±20% improvement) with optimum recipe conditions including composition, sintering process window that is part of this research effort. MxCy represents refractory metal carbides such as WC, Cr2C3, TiC that chemically reacts with B4C forming eutectic structure and contributing to increase in hardness and fracture toughness 6 to 16. The superhard (B4C -MxCy) system must be further investigated for such applications. By the combination of layered concept and composite structure (B4C-MxCy), the projected hardness, fracture toughness and ballistic performance should increase by 30-40% that will be confirmed under the proposed effort. Optimized architecture of B4C composite will bring a revolution in terms of light weight and better ballistic properties associated with increased dwell time, higher energy absorption and multi hit capability.