Preparation And Mechanical Properties Of Bioinspired Nacre-like Ni/Al₂O₃ Composites

Natural materials are typically composites arranged into complex,multiple-scale,hierarchical architectures.As such,they can display compelling combinations of mechanical properties,often far in excess of those of their constituent phases.They provide an ideal path for the development of high-strength,high-tough,lightweight structural materials in the future.However,these structures can seldom be well replicated synthetically.But the simpler ones,such as the brick-and-mortar structure of nacre,have been mimicked using a fine-scale,freeze-cast,ceramic brick-like scaffold infiltrated with a polymer.These bio-inspired nacre-like ceramics can indeed display excellent toughness,but it is impractical to achieve high-volume fraction?>90%?ceramic structures with freeze-casting and the polymeric compliant?mortar?phase clearly limits their high-temperature capability.Mostly,polymer mortars have been considered asthe ductile layer in brick-and-mortar composites.However,low stiffness ofpolymers does not efficiently transfer the shear between hard ceramic bricks.Moreover,theoretical modeling has suggested that higher strength and higher toughness is possible if a metallic mortar is utilized in place of the polymer.This can present problems for“top-down”freeze-cast processing techniques because high capillary pressures prevent complete infiltration as metals cannot readily wet ceramics.To avoid these issues altogether,we developed an alternative approach?“bottom-up”?to synthesize“nacre-like”structures ceramics containing a metallic nickel compliant phase.These materials were fabricated using“core-shell”alumina/nickel platelets that are aligned using magnetically assisted slip casting and sintered using hot-pressing.Through the analysis of the“core-shell”Ni/Al₂O₃sintering process,we analyzed the effects of sintering time,sintering temperature and volume fraction of Ni on the morphology and mechanical properties,so as to select suitable sintering conditions,optimize the sintering process,and prepare the Ni/Al₂O₃with optimum mechanical properties.With this process,we have successfully fabricated nacre-like metal/ceramic composite and have characterized their structure and mechanical properties.We avoid the dewetting of the nickel mortar during sintering by using Ni-coated platelets and hot-press processing.As a result,we have produced a bio-inspired nacre-like Ni/Al₂O₃ ceramic displaying a resistance-curve toughness up to 15.3MPa·m^1/2 with a flexural strength of 374 MPa and a fracture toughness of 8.4 MPa·m^1/2.The results show that this approach is promising toward development of bio-inspired nacre-like Ni/Al₂O₃ ceramic.