MICROSTRUCTURE AND STRENGTH OF CU-FE IN-SITU COMPOSITES OBTAINED FROM PREALLOYED CU-FE POWDERS

Copper-iron in situ composites have been produced from prealloyed, extruded powders. The extruded rods were subsequently cold drawn to various stains when the iron particles are drawn into fine fibres. The dependence of the tensile stress and the ductility on cold work has been analysed and the different microstructures have been examined to quantify their evolution with cold work. The fine scale of the initial microstructure makes it possible to obtain a high tensile stress after a relatively small reduction in area during working. The strength of such composites has previously been explained by models based on the rule of mixtures and these models are modified here to take into account the nanometre scale of the iron ribbons. Analysing the mechanical properties, it appears that the very fine scale of the ribbon-shaped iron particles makes them very strong such that they deform elastically up to very high stresses, even when the composite begins to deform in a non-elastic manner. The strength of the fine ribbons after very large drawing strain is considered to reach the theoretical limit, as the ribbons are reduced to thicknesses of about 3 nm, and beyond such strains the composite strength will probably increase at a slower rate or may saturate.