Experimental Relationships between the Fracture Behaviour and the Specimen Thickness in Fe-Ni-Co-C Martensitic Steels

Thin film specimens of both about 5μm and 20μm thickness and the ASTM standard sheet specimens of 1.6mm thickness were prepared using Fe-Ni-Co-C martensitic steels and were fractured in tension at room temperatue and at -196℃. Results of thin film specimens were compared with those of the ASTM standard specimens which showed very brittle behaviour. Fractography was investigated under both an optical microscope and S. E. M., and even cleavage facets were observed in the 5μm thick specimens. The observed behaviour supports mechanical results pretty well. Discussion is made on the view points of plane stress and plane strain conditions and of machine stiffness. The technique employed here and the results obtained are also examined to give a good information on studying mechanical properties of amorphous metal films.