Bioinspired Nacre‐Like Ceramic with Nickel Inclusions Fabricated by Electroless Plating and Spark Plasma Sintering

Abstract

Hybrid composites of layered brittle-ductile constituents assembled in a brick-and-mortar architecture are promising for applications requiring high strength and toughness. Mostly, polymer mortars have been considered as the ductile layer in brick-and-mortar composites. However, low stiffness of polymers does not efficiently transfer the shear between hard ceramic bricks. Theoretical models point to metals as a more efficient mortar layer. However, infiltration of metals into ceramic scaffold is non-trivial, given the low wetting between metals and ceramics. The authors report on an alternative approach to fabricate brick-and-mortar ceramic-metal composites by using electroless plating of nickel (Ni) on alumina micro-platelets, in which Ni-coated microplatelets are subsequently aligned by a magnetic field, taking advantage of ferromagnetic properties of Ni. The assembled Ni-coated ceramic scaffold is then sintered using spark plasma sintering (SPS) to locally create Ni mortar layers between ceramic platelets, as well as to sinter the ceramic microplatelets. The authors report on materials and mechanical properties of the fabricated composite. The results show that this approach is promising toward development of bioinspired ceramic-metal composites.Many structural materials are quickly approaching their performance limits. [1] There is an unmet demand for damage-tolerant, lightweight bulk structural composites for a range of applications including transportation, infrastructure, and for applications requiring operation in extreme environments, such as high temperature and high pressure. Damage tolerance refers to the ability of a material to exhibit simultaneous strength and toughness to resist propagation of cracks.

Bioinspired Nacre‐Like Alumina with a Metallic Nickel Compliant Phase Fabricated by Spark‐Plasma Sintering

“…A) Comparison of reported mechanical properties of bioinspired (nacre‐like) alumina ceramics containing less than 10 vol% metallic mortar, taken from refs. (circular data points), with that of nacre (triangular data point) and the current results (square and diamond data points) to illustrate how the composition, processing, and sintering temperature can affect their damage‐tolerance (strength and toughness). B,C) Scanning electron microscopy image of the path of a crack in natural nacre and Ni+NiO‐coated alumina sintered at 1100 °C (with a 25 µm scale bar), shows toughening via the pull‐out of the platelets (with displacements in the range of a few micrometers) leading to crack bridging, the coarser‐scale defection of the crack path, roughly perpendicular to orientation of the platelets, and the corresponding formation of a rough fracture surface as the crack tried to maintain a macroscopic path nominally perpendicular to the applied tensile stress.…”

“…The mechanical properties of our Ni+NiO‐alumina ceramics have high damage‐tolerance relative to other bioinspired ceramics with a <10 vol% metallic phase (Figure a). For example, a similar approach was used in a previous study, but the reported toughness values were an order of magnitude lower than the ceramics developed here, which may have originated from poor bonding between the ceramic and metallic phases (NiO‐coatings were not employed). Slip‐casting or freeze‐casting has also been used to process alumina/copper and alumina/nickel materials, and freeze‐casting has been employed to align Ni‐coated alumina platelets prior to hot pressing, but in all these cases the resulting toughnesses were significantly lower than the materials developed here, we presume due to extensive dewetting of the metallic phase.…”

“…For example, a similar approach was used in a previous study, but the reported toughness values were an order of magnitude lower than the ceramics developed here, which may have originated from poor bonding between the ceramic and metallic phases (NiO‐coatings were not employed). Slip‐casting or freeze‐casting has also been used to process alumina/copper and alumina/nickel materials, and freeze‐casting has been employed to align Ni‐coated alumina platelets prior to hot pressing, but in all these cases the resulting toughnesses were significantly lower than the materials developed here, we presume due to extensive dewetting of the metallic phase. The work of Garnier and Dunand is notable for its use of freeze‐casting to make nickel‐alumina composites but these did not replicate the structure and key mechanistic features of nacre due to the their high (≈30 wt%) nickel content, large nickel agglomerates (with diameters up to 6 µm) and consequent restricted brick sliding which compromises toughness.…”

Bioinspired alumina/reduced graphene oxide fibrous monolithic ceramic and its fracture responses

“…To describe the evolution of the crack extension length and crack growth resistance during crack propagation, the crack growth resistance curve (R‐curve) is usually calculated from a J‐integral by accounting for the local deflection and other dissipation mechanisms. This approach reflects the relationship between the fracture growth toughness ( K JC ) and crack extension length (Δ a ) extracted from the load‐displacement curves . Details on the R‐curve calculation are explained below.…”

“…This approach reflects the relationship between the fracture growth toughness (K JC ) and crack extension length (Δa) extracted from the load-displacement curves. 30,31 Details on the R-curve calculation are explained below.…”