Extraordinary Bauschinger effect in gradient structured copper

Abstract

Bauschinger effect is a well-known phenomenon, in which the tensile stress is higher than the reverse compressive stress. Here we report that the gradient structured copper exhibits an extraordinarily large Bauschinger effect. We propose to use the reverse yield softening, Δσ b , as a quantitative parameter to represent the Bauschinger effect. Δσ b evolves in the same trend as the back stress with pre-strain, and can be used to evaluate the effectiveness of a heterostructure in producing back stress for superior mechanical properties.

Perspective on hetero-deformation induced (HDI) hardening and back stress

“…In the following, we will present a brief history of the back stress concept, instead of a comprehensive review. Back stress is often related to the Bauschinger effect because they have the same physical origin [36][37][38][39]. In 1886 Bauschinger found that after an alloy was deformed plastically in tension, it exhibited a compressive yield strength lower than its tensile yield strength, and vice versa [40].…”

“…Back stress has been considered playing a critical role in the strengthening of metal matrix composites [44][45][46]. It is also often associated with Bauschinger effect [36,38,47,50]. However, neither back stress nor Bauschinger effect has been regarded as a major player in strengthening metallic materials by the general materials community.…”

“…As discussed above, back stress strengthening and work hardening have been believed responsible for the superior combination of strength and ductility of HS materials [1,2,39,61] as well as the Bauschinger effect [36,38,47,50]. To analyze this issue, let's look at the dislocation model of GND pile-up at an HS domain boundary in Figure 3.…”

Dynamically reinforced heterogeneous grain structure prolongs ductility in a medium-entropy alloy with gigapascal yield strength

“…Such actual experimental evidence is not available in the literature on HGSs, such as refs. 54 – 56 , where it was only argued that such behavior may be possible. More directly, we observe that the increase in internal back stresses (see SI Appendix , Fig.…”

Residual stress provides significant strengthening and ductility in gradient structured materials

“…In other words, dislocations gliding in the adjacent plastically deforming layers may be blocked and pile-up near the two elastic-plastic interfaces. The pile-up of GNDs generates long-range back stress in the plastic layer [15,[23][24][25][26][27][28][29][30][31]. The back stress needs to be balanced at the interfaces by forward-stress in the elastic layer, which contributes to the formation of the observed hardening belly, as shown in Figure 2(b).…”