Foams of gray cast iron as efficient energy absorption structures: a feasibility study

Abstract

Gray cast iron foams, were produced using a reticulated polyurethane by using a modified investment casting process. To evaluate the attributes of the produced micro-geometries, foam segments and single struts are investigated by light and electron microscopy in 2D, and synchrotron micro-computed tomography in 3D. Mechanical properties are determined by macro/micro-mechanical testing and nanoindentation. In the microstructure of the gray cast iron struts, both flake-like coarse type A and locally fine undercooled type D graphite particles are observed. The distribution of the two graphite types is heterogeneous and is the likely cause for the large scatter of the mechanical properties of the single struts. The high graphite content and the resulting brittle behavior of the struts lead to strong serrations in the stress-strain curve of the foams with a negative effect on energy absorption. We found a relatively low energy absorption efficiency of below 50% as compared to 75% in 316L austenitic steel struts. The small specimen size results in scale effects which strongly influence the mechanical properties of the foams. Further improvement in the fabrication of gray cast iron foams is needed to tailor graphite distributions and optimize performance of cast iron-based foams.