Enhanced cyclic deformation responses of ultrafine-grained Cu and nanocrystalline Cu–Al alloys

Improved Fatigue Strengths of Nanocrystalline Cu and Cu–Al Alloys

“…Originating from solid solution strengthening and finer grains with lowering of the SFE, the strengths of NC Cu and CuAl alloys can be drastically enhanced with increasing Al contents. [16,18,21,27] Compared with those prepared by ECAP, these NC materials exhibit substantially a higher strength due to the much more extensive grain refinement (Table 1). [16,18,21] However, different from the trends that the uniform elongation of NC Cu and CuAl alloys processed by ECAP presents a mild improvement with lowering of the SFE, [16,21] the ductility of the materials processed by HPT increases with the reduced SFE, but ultimately there is a reversal at the lowest SFE where the ductility decreases.…”

“…[6][7][8][11][12][13][14][15][16] As grain coarsening is a thermally activated process, [7,8,11,14] lowering the SFE by alloying can essentially restrict the closely relevant mechanisms, decrease the GB energy and then confine the GB migration. [16,31,32] Besides, the formation of twins with low excess energy, the interaction between Al atoms with GBs and the formation of short-range order (SRO) are also beneficial to the improvement of microstructures stability. [16,33,34] Although the formation mechanism of the shear bands during cyclic deformation is not well understood, this kind of surface damage was significantly lessened with lowering of the SFE as well, which could be attributed to the changed GB natures stemming from the lowered SFE.…”

“…[10][11][12][13][14] Recent results revealed that decreasing the stacking fault energy (SFE) via alloying design can significantly increase the fatigue strengths of the NC Cu-Al and Cu-Zn alloys processed by equal channel annular pressing (ECAP) through the enhancement of their tensile strengths and stabilization of the nanostructure via critically restricting the relevant mechanisms. [15,16] As well known, severe plastic deformation (SPD) processes remarkably affect the formation of nanostructures and corresponding mechanical properties. [17,18] Compared with ECAP, high-pressure torsion (HPT), another popular SPD technique, can produce remarkably finer grains and a higher fraction of high-angle grain boundaries (GBs) and then harvest higher tensile strengths.…”

“…This implies that SFE does play an intrinsic role in the fatigue strength, regardless of the kinds of SPD techniques applied, as revealed in Table 1. [15,16] Based on the well-known Basquin law, the reversal fatigue life is closely related to the stress amplitude in a fully reversed, constant-amplitude fatigue test as expressed in the following form [10]:…”

Effect of the stacking fault energy on the mechanical properties of pure Cu and Cu-Al alloys subjected to severe plastic deformation

“…In addition to the development of the increased microstructural homogeneity, the average grain size is also decreasing with decreasing SFE and lower processing temperature due to the limited dynamic recovery and change of the dominant refinement mechanism from the dislocation one to twin fragmentation mechanism [26].…”