Bioinspired nacre-like alumina with a bulk-metallic glass-forming alloy as a compliant phase

Abstract

Bioinspired ceramics with micron-scale ceramic “bricks” bonded by a metallic “mortar” are projected to result in higher strength and toughness ceramics, but their processing is challenging as metals do not typically wet ceramics. To resolve this issue, we made alumina structures using rapid pressureless infiltration of a zirconium-based bulk-metallic glass mortar that reactively wets the surface of freeze-cast alumina preforms. The mechanical properties of the resulting Al 2 O 3 with a glass-forming compliant-phase change with infiltration temperature and ceramic content, leading to a trade-off between flexural strength (varying from 89 to 800 MPa) and fracture toughness (varying from 4 to more than 9 MPa·m ½ ). The high toughness levels are attributed to brick pull-out and crack deflection along the ceramic/metal interfaces. Since these mechanisms are enabled by interfacial failure rather than failure within the metallic mortar, the potential for optimizing these bioinspired materials for damage tolerance has still not been fully realized.

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.…”

“…There has been great interest in mimicking this nacre‐like structure to generate high‐toughness ceramics. Processing techniques such as freeze‐casting (ice templating), layer‐by‐layer alignment, thermal spray processing, sedimentation, coextrusion, magnetic platelet alignment, and vacuum filtration assisted alignment have been used to recreate brick‐and‐mortar microstructures. Using polymeric mortars, the nacre‐like ceramics avoid sudden catastrophic failure by stabilizing slow crack growth in the form of crack‐resistance (R‐curve) behavior, although they cannot be used at elevated temperatures due to the presence of polymer phase .…”

Strong and tough nacre-like aluminas: Process–structure–performance relationships and position within the nacre-inspired composite landscape

“…Because of Griffith scaling law, smaller reinforcement sizes usually mean stronger composites, so the next development was to use micron-sized bricks, with alumina platelets [45,46,47], glass flakes [33,48], or brushite platelets [49]. Several secondary phases have been used in these composites, from polymers [47,50,51] to metal [52,53,54,55,56] and even graphene [57] or metallic glasses [58]. The controlled dewetting of TiO 2 nanolayer allows in addition the careful study of the mineral bridges' effect on the mechanical properties [59,60].…”

Synthesis of bioinspired ice-templated bulk metallic glass-alumina composites with intertwined dendritic structure

“…Indeed, the synthesis of various freeze-cast materials has stimulated widespread studies on the development of polymer-ceramic, metal-ceramic, and metal-metal composites with ice-templated reinforcements [20][21][22]. While conventional alloys like aluminum or copper have been utilized to infiltrate the freeze-cast foams and produce the composites with anisotropic architectures, BMs have been rarely used in the synthesis of the icetemplated composites [23].…”

“…The Zr46Cu30.14Ag8.36Al8Be7.5 (in at.%) BM ingots were fabricated by arc melting a mixture of pure elements and a commercial Cu77.3Be22.7 alloy under a Ti-gettered Ar atmosphere, which were then cast into a copper mold.. Alumina preforms with interconnected pore channels showing a dendritic pore morphology ( Figure 1a) were prepared by freeze-casting [23]. The freeze-cast alumina was infiltrated with the BMforming melt using a quartz tube with inner diameter of 5 mm (Figure 1b).…”