| Composite Metal Foam (CMF), a new material belonging to the class of advanced cellular and porous materials, has been successfully processed using Gravity Casting technique for the first time at NC State University. This material comprises of steel hollow spheres and a solid Aluminum alloy matrix. The complete characterization of the material included mechanical testing such as monotonic compression, compression-compression fatigue, micro hardness, nano hardness and higher strain rate compression. The energy absorption behavior of the material under static compression has been studied extensively. Experimental results show that Al-steel CMF not only has a higher energy absorption capability than that of other commercially available metal foams produced from similar materials, but also possess a higher strength to density ratio. The microstructural analysis of the material was used to study and explain the formation of different phases at the Aluminum-Steel interface and their effect on the deformation behavior of the composite foam under compression. The effect of processing temperature on the microstructure of the composite metal foam and specifically on the sphere-matrix interface was studied by experimental means. The mechanical properties of the ternary phases formed in the microstructure of the composite foam were characterized using micro and nano-hardness tests. The phases were chemically characterized and formulated using Energy Dispersive Spectroscopy analysis and Al-Fe-Si alloy ternary phase diagrams. The fatigue behavior of the composite metal foams was studied under compression-compression fatigue loading and the results were compared with those of other closed cell metal foams. The elastic modulus of the foams was evaluated using experimental and analytical techniques and the results were found to be in good agreement. Composite metal foams were also processed using a higher solidification rate with water cooling. The effect of alterations in microstructure on the mechanical properties of the composite metal foams was studied and results presented. As the result of high strength, the increase in energy absorption of the composite metal foam samples ranges over thirty times compared to that of 100% Al foams and over six times compared to that of 100% steel foams. |
