A novel biomimetic approach to the design of high‐ performance ceramic/metal composites Maximilien E. Launey 1 , Etienne Munch 1,† , Daan Hein Alsem 1,2 , Eduardo Saiz 1 , Antoni P. Tomsia 1 and Robert O. Ritchie 1,3,  1 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 2 National Center for Electron Microscopy, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA 3 Department of Materials Science and Engineering, University of California, Berkeley, California, 94720, USA Abstract The prospect of extending natural biological design to develop new synthetic ceramic/metal composite materials is examined. Using ice‐templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine‐scale laminated ceramic/metal (bulk) composites that are inexpensive, lightweight, and display exceptional damage‐tolerance properties. Specifically, Al 2 O 3 /Al‐Si laminates with ceramic contents up to ~40 vol.% and with lamellae thicknesses down to 10 μm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa√m at a tensile strength of ~300 MPa. Salient toughening mechanisms are described together with further toughening strategies. Keywords: ceramics; metals; composites; toughness; strength; freeze casting Present address: Manufacture Francaise des Pneumatiques Michelin, 63040 Clermont Ferrand, France Author for correspondence (roritchie@lbl.gov)

A novel biomimetic approach to the design of high-performance ceramic/metal composites

Temperature-dependent reversed fracture behavior of multilayered TiBw/Ti–Ti(Al) composites

Nacre's multiscale reinforcing mechanisms provide lessons for the design and fabrication of high-performance engineering composites. In this study, the addition of hierarchically aligned flake Al2O3 and reduced Graphene Oxide (rGO) nanosheets into Al matrix constitute the bioinspired multiscale Al2O3-rGO/Al laminated composite via flake powder metallurgy. The results show that multiscale Al2O3-rGO reinforcements have the synergistic strengthening effect of 1 + 1>2. Extra strengthening mechanism is attributed to enhanced load transfer due to good bonding at Al2O3/rGO/Al interface. Compared to Al2O3/Al composite, the uniform elongation of Al2O3-rGO/Al laminated composite doesn't decrease due to the higher strain hardening capacity. The work presented here provides a new strategy for developing advanced composites with simultaneous enhancement of the modulus-strength-ductility.

Bioinspired multiscale Al2O3-rGO/Al laminated composites with superior mechanical properties

The relationship between different ball milling (BM) conditions and mechanical properties of CNT/Al composites was studied through tailoring grain interior/grain boundary affected zone (GI/GBAZ). The ultrafine-grained (UFGed) architectures of the CNT/Al composites made from flake powders with the same thickness under different BM conditions, introduce different strain rates and vary dislocation density. The results showed that the grain size of CNT/Al composite were significantly influenced by milling conditions, which caused obvious variations in mechanical properties. The enhancing in tensile properties of CNT/Al composite mostly caused by grain refinement, dislocation strengthening, and back stress hardening, which last two terms are closely linked to GBAZ thickness. The simulated results agreed well with experimental results, confirming a strain rate dependency of GBAZ thickness. This work strengthened the understanding of ball milling process on the microstructure and mechanical properties of metal matrix composites.

Enhanced mechanical properties of CNT/Al composite through tailoring grain interior/grain boundary affected zones

Tuning solidification microstructure remains a grand challenge for ceramic particles reinforced Al-Si based composites due to adverse interactions between ceramic particles and Si-containing melts. This work proposed a novel in-situ synthesis strategy of designing master alloys decorated with well-dispersed TiCxNy and TiB2 particles to synergistically optimize the Al-Si based composites. By adjusting the reactant contents and ratios, near-spherical nano-sized TiCxNy particles and hexagonal submicron-sized TiB2 particles were obtained in as-synthesized Al-(TiCxNy-TiB2)p master alloys. The effects of this pre-dispersed agent on solidification kinetics, microstructure features and mechanical performance evolution of the Al-10Si-2Mg composites were investigated in detail. TiCxNy-TiB2 particles could trigger the heterogeneous nucleation of primary α-Al crystals, and the growth-restricting effects also contributed to grain refinement, which finally accounted for the enhancement in both strength and ductility. This work is expected to provide new guidance for selection of reinforcing particles and synergistic optimization of the solidification microstructure and performance. 

Synergistic optimization in solidification microstructure and mechanical performance of novel (TiC N − TiB2)p/Al nanocomposites: Design, tuning and mechanism

Inspired by nacre’s design principle, a bottom-up strategy by self-assembly alignment of flake powders, namely flake powder metallurgy, is employed to fabricate bioinspired laminated composites with brick-and-mortar structure. The microscale flake Al2O3 powders and flake Al powders with native Al2O3 nanolayers are utilized to fabricate the bioinspired hierarchical Al2O3/Al laminated composites, and the composites with 5 vol% Al2O3 achieves an enhancement of 22% in strength with only a 7% compromise on ductility, leading to a notable improvement in toughness (17%) compared to the corresponding Al matrix. The higher strain hardening due to enhanced dislocation accumulation capacity at hierarchical Al2O3/Al interface can delay the occurrence of necking, and the large elongation after peak stress is attributed to multiple extrinsic toughening effect from brick-and-mortar structure. The bottom-up strategy can guide the design and fabrication of advanced bioinspired laminated composites to achieve enhanced mechanical performance.

Bioinspired hierarchical Al2O3/Al laminated composite fabricated by flake powder metallurgy

In the study, a roughened interface is designed to achieve the strength-ductility synergy of Al2O3/Al composites fabricated by flake powder metallurgy. The roughened SiO2@Al2O3 platelets are fabricated by high-shear dispersion process and subsequent sintering at the high temperature. The results show that different morphologies of asperities on the surface of SiO2@Al2O3 platelets can be obtained via controlling the sintering time. As the roughness increases, the strength and ductility of SiO2@Al2O3/Al composites are simultaneously improved. Load transfer efficiency is enhanced by platelet-matrix interlocking at the roughened SiO2@Al2O3/Al interface, compared to Al2O3/Al composite with smooth Al2O3–Al interface. The improved tensile ductility in SiO2@Al2O3/Al composite is attributed to the extrinsic toughening mechanism. This design strategy offers a simple and promising approach to improve the mechanical properties of metal matrix composites.

Haitao Zhao

Papers

Bioinspired hierarchical Al2O3/Al laminated composite fabricated by flake powder metallurgy

Bioinspired multiscale Al2O3-rGO/Al laminated composites with superior mechanical properties

Towards the strength-ductility synergy of Al2O3/Al composite through the design of roughened interface