Bio-Inspired Nacre-Like Ceramic Matrix Composites

Understanding the role of the ductile polymer phase in mechanical behavior of bioinspired hybrid composites is an important step toward development of materials with damage tolerant properties. In this dissertation,fabrication and characterization of a bioinspired lamellar composite by incorporation of a semicrystalline polymer into a freeze-casted scaffold is reported. The elastic modulus and ductility of the polymer phase can be changed by more than three and fifty five times, respectively, in addition to forty two folds decrease in modulus of toughness, by thermal annealing post-processing, after infiltration into the freeze-casted ceramic scaffold. The results show that although polymer phase affects the fracture toughness and flexural behavior of the composite, the drastic changes in mechanical properties of the polymer phase has only marginal effects on the resulted properties of the composite. In situ SEM experiments and finite element simulation were used to investigate the deformation mechanism and the effect of the polymer phase on the distribution of stress in the fabricated composites. Additionally, a metal-ceramic composite comprised of ~82 vol. % alumina (Al2O3) and ~18 vol. % nickel (Ni) was fabricated via co-assembly of alumina micro-platelets with Ni particles using the freeze-casting process followed by the spark plasma sintering (SPS). The SPS processing with a custom-designed temperature-pressure history resulted in formation of elongated Ni phase between the lamellar-ceramic phase. Results of the mechanical characterization showed that inclusion of Ni improveed the flexural strength of the composite by more than 47% compared to the lamellar ceramic. Additionally, the crack initiation (KIC) and crack growth toughness increaseed by 20% and 47%, respectively. The inclusion of softer Ni phase did not compromise the indentation modulus and indentation hardness of the composite compared to the pure ceramic. Infiltration of a molten metal phase into a ceramic scaffold to manufacture metal-ceramic composites often involves high temperature, high pressure, and expensive processes. Low-cost processes for fabrication of metal-ceramic composites can substantially increase their applications in various industries. In this disseration, electroplating (electrodeposition) as a low-cost, roomtemperature process is demonstrated for infiltration of metal (copper) into a lamellar ceramic (alumina) scaffold. Estimation shows that energy consumption of this process is less than a few percent of the conventional molten metal infiltration process. Characterization of mechanical properties showed that metal infiltration enhanced the flexural modulus and strength by more than 50% and 140%, respectively, compared to the pure lamellar ceramic. More importantly, metal infiltration remarkably enhanced the crack initiation and crack growth resistance by more than 230% and 510% compared to the lamellar ceramic. The electrodeposition process for development of metal-ceramic composites can be extended to other metals and alloys that can be electrochemically deposited, as a low-cost and versatile process.