Mechanical behavior of nickel base foams for diesel particle filter applications

Open-cell Ni foams are mainly used as battery electrodes. The very large specific surface of the INCOFOAM pure Ni foams also leads to outstanding filtration properties. A Diesel Particulate Filter (DPF) application requires the alloying of the INCOFOAM material to improve the oxidation resistance and to provide thermal stability. For that purpose, a foam alloying route using powder metallurgy was developed by INCO and IFAM (patent number: DE 103 01 175.7). The alloyed foams designed for the DPF application are named INCOFOAM HighTemp. The typical alloy composition of the foams studied in this work is that of Inconel 625. The objective of the work is to provide tools for the design of DPF considering critical aspects of the life-time of a real filter, from its manufacturing to the in service conditions. The manufacturing of complex filter shapes can induce damage in the foam that could affect the durability of the filter component. Creep in the filter is likely to start during high temperature regeneration regime. A predictive model for tensile properties for both Ni and alloyed foams is presented. It assumes that the bending of the struts is the main deformation mechanism in the foam. A simplified morphology is deduced from 3D reconstruction of microtomography of Ni foams, 2D image analysis and electrical resistivity measurements. Creep of alloyed foams is also investigated in this work. Two creep mechanisms are evidenced from the experimental point of view and we confronted an existing model to a large experimental data set of alloyed foams creep measurements. The proposed model describes better high temperature creep than low temperature creep. A 3D investigation of microtomographic foam images with the Finite Elements Method is finally used in order to assess the assumptions of the models presented before.