Nondestructive In-situ Strength Analysis of High-strength Metal with Nano-size Microstructure

In-situ neutron diffraction measurement was conducted to investigate the plastic deformation and fatigue damage behavior of ultrafine-grained high-strength Cu processed by equal channel angular pressing, ECAP. The experiments were conducted on the ultrafine-grained samples, as well as large-grained counterparts, under tensile and fatigue loading using RESA of Japan Atomic Energy Agency. The diffraction profiles were analyzed in relation with the applied stress, strain and fatigue damage. The result of the large-grained samples shows that the full width at half maximum, FWHM, of the profile from 311 diffraction plane increases with increasing applied stress and that the FWHM remains large even when the sample is unloaded due to accumulated plastic strain. On the other hand, the result of the ultrafine-grained samples shows that the FWHM decreases to the original value upon unloading even after the plastic deformation. The similar results were observed in the process of low-cycle fatigue. The decrease in the FWHM in the ultrafine-grained sample is attributed to the rearrangement of transgranular plastic strain in ultrafine grains.