Mechanical and fracture behaviour of the three-scale hierarchy structure in As-deposited and annealed nanocrystalline electrodeposited Ni–Fe alloys

• Published in: Journal of materials science 2019-10, Vol.54 (20), p.13378-13393
• Main Authors: Maizza, G., Eom, H., Lee, M., Yim, T. H., Nakagawa, E., Pero, R., Ohmura, T.
• Format: Article
• Language: English
• Subjects: Alloys; Anisotropy; Annealing; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Crystallography and Scattering Methods; Degassing of metals; Elongation; Foils; Fracture testing; Grain structure; Hardness; Image resolution; Iron; Magnetic properties; Materials Science; Mechanical properties; Metals; Metals & Corrosion; Microstructure; Nanocrystals; Nanoindentation; Nickel base alloys; Polymer Sciences; Solid Mechanics; Specialty metals industry; Tensile strength
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-019-03835-8

The growing interest in nanocrystalline (nc) materials is driven by their outstanding combination of mechanical and functional properties. Electrodeposited nc Ni–Fe alloys have received considerable attention, thanks to their unique strength and to their thermal and magnetic properties. However, the research on the relationship between microstructure, mechanical properties and fracture behaviour, under both As-deposited and annealed conditions, is still rather limited. In this paper, 48 wt% Fe electrodeposited nc Ni–Fe alloy foils were tested, by means of tensile and nanoindentation tests, under both As-deposited and annealed conditions (300–800 °C). High-resolution FESEM images revealed that the As-deposited microstructure consisted of an unforeseen, evident anisotropic nested three - scale hierarchy nc structure, namely from the nanocrystalline (~ 10 nm) to the sub-micron (up to 250 nm) scale, across a mesostructure (155–165 nm), here denoted as the characteristic grain structure . Such a nested nc grain structure of the electrodeposited nc Ni–Fe alloy, which resembles the one of a corncob ( corncob - like structure), explained the unique anisotropic mechanical properties of the foils after nanoindentation, tensile and oblique-bending fracture tests. The mechanical properties ( i.e. tensile strength, elongation, yield strength and hardness) of the foils annealed up to 320 °C were found to be improved, in comparison with the As-deposited counterparts, whereas those annealed above 320 °C were deteriorated.