Tensile strength and ductility of ultra-fine-grained nickel processed by severe plastic deformation

Experimental Investigation of the Equal Channel Forward Extrusion Process

“…This can be due to a decreasing of the internal strains and accumulation of internal energy, therefore, increasing the possibility for crack formation, or it can be related to the increase of the strain rate sensitivity of the material, which causes resistance to neck formation. This improvement of the mechanical properties of material behavior using the ECFE process has also been reported for Al1050, Al6061, Al7075, and nickel during the ECAP process [26,27,29,30] and Al-3%Mg-0.2%Sc during the HPT process [31]. In addition, the ECAP process on the same material, reported by Tolaminejad and Dehghani [32], indicated that about 64% and 108% enhancement of the hardness value and approximately 202% and 267% improvement at the yield strength magnitude have been achieved after the first and fourth passes when compared to the annealed condition.…”

“…Although the elongation to failure magnitude is increased slightly at the fourth pass, its magnitude is 66% lower than the aluminum under annealed conditions. The slight increase in the elongation to failure for the fourth-pass ECFE aluminum, as compared to the first pass (7%) can be related to the occurrence of grain boundary recovery (conversion of LAGBs to HAGBs) [26][27][28]. This can be due to a decreasing of the internal strains and accumulation of internal energy, therefore, increasing the possibility for crack formation, or it can be related to the increase of the strain rate sensitivity of the material, which causes resistance to neck formation.…”

The Strength–Grain Size Relationship in Ultrafine-Grained Metals

“…[140] For example, Fig. 13 contrasts the YS of Ni after HPT or ECAP and rolling [141] with that of electrodeposited Ni [142][143][144] shown by the continuous line which corresponds to σ o ≈ 7 MPa and k y ≈ 5.7 MPa.mm 1/2 . For the latter condition, the grains contain no dislocation substructure and normal H-P behavior is observed.…”

“…The upper dashed line is for UFG Ni processed by HPT or ECAP and subsequent rolling in order to achieve a higher strength. [141] The YS in this case may be calculated by adding the contribution of LAGBs and HAGBs and the non-equilibrium grain boundaries [NGBs] so that [140] σ y = σ o + σ LAGB + σ HAGB + σ NGBs [4] and…”

“…[135] Figure 13. Superstrength in Ni subjected to ECAP and subsequent rolling; [140] the dashed line shows UFG Ni [141] and the solid line shows H-P behavior in nano-Ni fabricated by electroplating. [142][143][144] Figure 14.…”