Significant contribution of stacking faults to the strain hardening behavior of Cu-15%Al alloy with different grain sizes

Abstract

It is commonly accepted that twinning can induce an increase of strain-hardening rate during the tensile process of face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE). In this study, we explored the grain size effect on the strain-hardening behavior of a Cu-15 at.%Al alloy with low SFE. Instead of twinning, we detected a significant contribution of stacking faults (SFs) irrespective of the grain size even in the initial stage of tensile process. In contrast, twinning was more sensitive to the grain size, and the onset of deformation twins might be postponed to a higher strain with increasing the grain size. In the Cu-15 at.%Al alloy with a mean grain size of 47 μm, there was a stage where the strain-hardening rate increases with strain, and this was mainly induced by the SFs instead of twinning. Thus in parallel with the TWIP effect, we proposed that SFs also contribute significantly to the plasticity of FCC alloys with low SFE.

Ductility Sensitivity to Stacking Fault Energy and Grain Size in Cu–Al Alloys

“…The strain-hardening rate of the Cu-15Al alloy is slightly lower than the Cu-11Al alloy when the grain size is about 0.6 μm, as shown in Figure 3(a), and the plastic deformation is largely undertaken by SFs and DTs since only few dislocations were detected in the Cu15Al alloy. [18] When the grain size is further increased to 1.5 and 3 μm, it is found that the strain-hardening rates especially at the later tensile process are comparable between the Cu-11Al and Cu-15Al alloys, as shown in Figure 3(b) and 3(c), which may be related to the dominating deformation modes of SFs and DTs. [18,27] It is observed that the flow stress of the Cu-15Al alloy is much higher than the Cu-11Al alloy as shown in Figure 3(a)-(c), thus resulting in a lower ductility in the Cu-15Al alloy though comparable strain-hardening rate is achieved.…”

“…In contrast, only few dislocations can be detected when the SFE is smaller than 8 mJ/m 2 , but SFs and DTs play important roles in the tensile deformation process. [18] These different deformation mechanisms dominated by grain size and SFE are supposed to determine the strain-hardening behavior, thus the tensile plasticity of the Cu-Al alloys.…”

“…[17] In contrast, when the SFE is low, dislocation slip in the planar mode dominates and dislocation recovery will be inhibited; besides, stacking faults (SFs) and deformation twins (DTs) prevail. [15,18] Thus SFE should impact crucially on the ductility of FCC alloys via determining the strain-hardening behavior.…”

“…[12,13,18,20,26,28] After characterizing the microstructures after tensile tests, the deformation patterns of the Cu-Al alloys with different SFEs and grain sizes were summarized and schematically shown in Figure 2. When the SFE is higher than 30 mJ/m 2 , only dislocation configurations were detected during tensile test in this study when the grain size is larger than about 1 μm.…”

“…[19][20][21] In contrast, fully recrystallized twinning-induced plasticity steels and Cu-Al alloys with grain sizes smaller than 1 μm have been fabricated by cold rolling and annealing process, [18,22,23] which makes it feasible to study the ductility and deformation mechanisms from the finegrained regime to the coarse-grained regime.…”