Mechanical behavior of bulk nanocrystalline Cu and Fe materials obtained by isostatic pressing and sintering

This report gives results of a study on the mechanical properties of bulk nanocrystalline Fe and Cu samples consolidated from nanometric powders prepared by levitation melting in liquid nitrogen. Both X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) have been used to determine average grain size. Bulk nanocrystalline compacts were obtained by cold isostatic pressing over a pressure range of 500 to 1000 MPa (72 to 145 ksi). After compaction, sintering under specific conditions was carried out. Sample density range from 60 to 90%25 of the theoretical values and grain size between 60 to 70 nm. The mechanical properties of these samples were investigated by compression testing performed on cylindrical shaped specimens with active length of 8 mm (0.315 in) and diameter of 4 mm (0.157 in). The yield strength in both Fe and Cu bulk nanometric materials was far above the strength of the coarse-grained standards. Bulk nanometric grained Fe was very strong and brittle, presenting a yield and ultimate tensile strength of 1300 MPa (188.5 ksi) and fracture occurred at strains <3%25. Bulk Cu nanocrystalline samples presented a yield strength of 245 MPa (35.5 ksi), ultimate strength of 480 MPa (69.6 ksi) and fracture occurred at strains of almost 15%25.

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