Influence of Strain Rate on Mechanical Behaviours of Gradient-Structured Copper

Abstract

The mechanical properties of gradient-structured (GS) pure Cu processed by surface mechanical attrition treatment (SMAT) were investigated by tensile tests at different strain rates in the range of 5 × 10⁻⁴ s⁻¹ to 5 × 10⁻² s⁻¹ at room temperature. The yield strength (YS), ultimate tensile strength (UTS) and ductility (uniform elongation, UE) of the gradient-structured Cu are simultaneously increased with increasing strain rate, especially for the sample processed by longer SMAT-treating time, while the coarse-grained (CG) Cu showed no obvious strain rate effect on strength and ductility. In addition, the strain rate sensitivity (m) and hetero-deformation induced (HDI) stress of the gradient-structured samples also increased with increasing strain rate. The increase in strength is mainly attributed to the gradient-structured layers and HDI stress strengthening. On the other hand, the increase in ductility can be attributed to an increase in strain rate sensitivity (m) and the strain hardening induced by the accumulation of a large number of geometrically necessary dislocations (GND_S) caused by a large stress gradient (HDI hardening).

Fig. 10 (a) Engineering stress-strain curves of gradient-structured surface layer and coarse-grained core obtained at two different strain rates. (b) Schematic illustration of the stress gradient effect and microstructure in SMAT-processed samples.