Influence of Heat Treatment on Microstructure Evolution and Yield Surfaces of Ni/PU Hybrid Foams

Metal foams are characterized by low weight, high resource efficiency, high relative stiffness, and exceptional energy absorption capacity under compressive load. Nickel/polyurethane (Ni/PU) hybrid foams consist of an open-cell polyurethane foam coated with a layer of nickel produced by electrochemical deposition. The coating of the PU foams takes place in a flow reactor, in which the electrolyte is pumped through the foam at a defined flow velocity. The macromechanical properties of foam-like structures depend on the structure of the skeleton, the inherent material properties and, in the case of Ni/PU hybrid foams, the properties of the electrochemically generated nickel layer. To influence their mechanical properties, the Ni/PU hybrid foams are subjected to heat treatment. In the given experimental setup, the parameters flow velocity, temperature, and duration of the heat treatment are each investigated at two different levels. Thus, interactions between the initial microstructure and the type of heat treatment are evaluated by means of X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) measurements. Interactions between initial mechanical properties and heat treatment are investigated by uniaxial compression tests and superimposed compression-torsion tests. The knowledge gained is used to control the macromechanical properties of the hybrid foam. This contribution focuses on potential effects on the electrochemically produced nickel layer of Ni/PU hybrid foams both during production and in a subsequent heat treatment, their interactions and the determination of correlations between microstructure and mechanical properties under uniaxial and multiaxial loading. Microstructural phenomena are observed using in situ X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements.image (c) 2024 WILEY-VCH GmbH