Local Strain Measurement in Hot Deformed Microstructures

Abstract

The deformation of metals at high homologous temperatures typical of industrial forming processes such as hot rolling is investigated using an electron micro-lithography technique enabling strain measurements at the scale of the microstructure of these metals. Grids with a typical 5 μm pitch have been laid on the surface of an aluminium alloy and a stainless steel deformed by plane strain compression at 400oC and 850oC respectively. In-plane strain values can be computed from the displacements of the intersections of the grids. Strain maps can then be plotted over representative areas of the microstructures together with strain distributions within each phase of the microstructure. Results obtained for a commercial high-purity aluminium alloy with 5% magnesium show a strong localisation of deformation at triple points with a local equivalent strain value of 1.7 for a 0.22 applied strain at 400oC. As for the two-phase stainless steel deformed to a strain of 0.3, results show a high heterogeneity of deformation within each phase with a localisation of deformation into bands in the ferrite phase and local values reaching more than two times the applied compression.