Microstructural changes in the cell walls of a closed-cell aluminium foam during creep

Abstract The microstructure of an Alporas® foam was examined both before and after creep deformation. It was found that the initial microstructure of the foam consists of subgrains which are several micrometres in size. Because of the complicated distribution of the applied stress in a foam, the corresponding microstructure development is rather inhomogeneous during creep. The microstructure may change drastically by choosing different investigated areas in the same deformed foam. In most areas, no evident changes in microstructure can be seen in comparison with the initial microstructure; however, in strongly deformed areas, subgrains with a much smaller average size are found, and the shape of these subgrains is equiaxed. The stress estimated from the subgrain size reveals that locally very high stresses must have existed during creep deformation, which may reach the power-law breakdown regime. This is a reasonable explanation of the high stress exponent obtained for Alporas® foams.