A metal-ceramic composite comprised of %82 vol% alumina (Al 2 O 3 ) and %18 vol% nickel (Ni) is 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 result in formation of elongated Ni phase between the lamellar-ceramic phase. Results of the mechanical characterization shows that inclusion of Ni improves the flexural strength of the composite by more than 47% compared to the lamellar ceramic. Additionally, the crack initiation (K IC ) and crack growth toughness increase by 20% and 47%, respectively. The inclusion of softer Ni phase does not compromise the indentation modulus and indentation hardness of the composite compared to the pure ceramic.Inclusion of a ductile metal phase into a ceramic matrix can improve its fracture toughness, in addition to other possible desirable properties such as electrical conductivity. [1][2][3] Such metal-ceramic composites have applications and market demand in various industries including automotive, aerospace, oil, and defense, in products such as high performance wearresistance parts, cutting tools, light-weight structural composites, and aero-engine components. [4,5] Metal inclusion can be either in the form of randomly distributed particles, layered (lamellar), or nature-inspired brickand-mortar architecture. Based on the desired structure, there are various processes for preparation of metal-ceramic composites. They include (but not limited to) stir-casting, tape-casting and tape-sintering, squeeze-casting, thermal spraying of multilayered ceramic-metal, hot pressing, freeze-casting, and spark-plasma sintering, among others. [1][2][3][5][6][7][8][9] In certain cases, a combination of these processes is used to fabricate the metal-ceramic composite. Often it is desired that the metal phase to have small volume percentage to achieve a good balance of strength and toughness in the composite. [10] This requirement imposes further processing challenges, in particular for lamellar and brick-and-mortar architecture, since the pore size to be filled with metal mortar is small.The overall toughening mechanism of metal inclusion into ceramic is believed to be a combination of several factors including (but not limited to) energy dissipation associated with the plastic deformation of the metal phase, crack tip blunting, deflection of the crack at the metal-ceramic interface, and reduction of stress concentration by distribution of the crack to a larger area. [1][2][3] In the case of lamellar and brick-and-mortar architecture, the ductile metal phase can also function similar to a lubricant, which relieves stress concentration by allowing for limited sliding. The ductile metal phase may also provide crack bridging as an extrinsic crack-tip shielding mechanism. [7,11] These mechanism overall are manifested in the form of a rising R-curve behavior.In several early works alumina-Ni composites have been reported, in which ...
