The influence of some microstructural and test parameters on the tensile behaviour and the ductility of a mechanically-alloyed Fe–40Al alloy

The present study examines the influence of a wide range of microstructural parameters and tensile test conditions on the tensile behaviour of a mechanically-alloyed, fine grained Fe–40Al intermetallic. Major changes of tensile strength and ductility are obtained by reducing the grain size (with the ductility increasing from 1 to 10% for grain sizes of 100 and 1 μm), by avoiding environmental attack during the test, and by avoiding premature stress/strain concentrators (with the ductility increasing from 5 to 10% as imperfectly machined samples have their sample surfaces polished). Ductility variations are interpreted using a model based on the slow propagation of an initial crack which eventually reaches a condition of instability, and where the respective roles of environment, plastic deformation processes, and fracture mechanisms can be distinguished. The tensile ductility is highly sensitive to the surface state, meaning the degree of exposure to the environment, the extent of geometrical stress raisers, and the microstructure made up of the grain and particle size and distribution.