Optimising in-situ nitridation in piled aluminium flakes for novel closed cell composites with high fracture stress and toughness

Publication date: 15 July 2018
Source:Materials & Design, Volume 150
Author(s): Andrey A. Chernousov, Ben Y.B. Chan
Modified aluminium foams, such as syntactic aluminium foams (SAFs) that contain tiny ceramic hollow spheres, are widely used for the protection of modern lightweight vehicles in mechanical impacts. Due to the typical compromises between strength and toughness, conventional SAFs absorb <5 J g⁻¹ of mechanical energy before fracture.In this study, we demonstrate that a nacre-like structure of piled aluminium flakes with in-situ grown AlN layers can provide a specific toughness of up to ~50 J g⁻¹. At the optimum toughness, the compressive yield strength σ0.2%, fracture strength σT and strain εT reach ≈110 MPa, 481 MPa and 0.35, respectively. The improved properties originate from the efficient nitridation-driven spreading of the partially melted Al of the flakes through the permeable nitride layers. In an N2 atmosphere at about 833 K, an optimal composite structure is formed with a porosity ϕE and AlN volume fraction vAlN of 0.26 and 0.12, respectively. The pre- and post-optimal annealing temperatures lead to a relatively small area of Al-AlN bonding, as a result of overgrowth and undergrowth of the AlN surfaces, respectively.This straightforward technology offers an affordable way to produce novel lightweight composites for state-of-the-art protection of vehicles and dynamic machinery in many industrial areas.

Graphical abstract

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