In situ SEM characterization of tensile behavior of nano-fibrous Al–Si and Al–Si–Sr eutectics

In situ tensile testing in a scanning electron microscope was used to study the effects of fiber orientation and colony boundaries in laser-refined fully eutectic Al–Si and Al–Si–Sr alloys. In Al–Si alloy, the measured tensile stress–strain response in samples from single colonies is highly dependent on the orientation of Si nanofiber relative to the loading direction. Tensile samples with multiple colonies exhibit improved strain hardening but the measured ductility was limited by cracking along inter-eutectic colony boundaries. The Al–Si eutectic alloys, doped with Sr and processed with finer spot size laser beam, exhibit higher yield strength in samples from single colony due to refined fiber diameter and inter-fiber spacing of nanoscale Si fibers. As a consequence, samples with multiple colonies exhibit sliding or cracking at eutectic colony boundaries before significant uniform elongation developed within the colonies. The low ductility of Al–Si–Sr sample could be ascribed to the reduced shear strength of colony boundary induced by Sr element addition.