Revealing Extraordinary Intrinsic Tensile Plasticity in Gradient Nano-Grained Copper

Abstract

Nano-grained (NG) metals are believed to be strong but intrinsically brittle: Free-standing NG metals usually exhibit a tensile uniform elongation of a few percent. When a NG copper film is confined by a coarse-grained (CG) copper substrate with a gradient grain-size transition, tensile plasticity can be achieved in the NG film where strain localization is suppressed. The gradient NG film exhibits a 10 times higher yield strength and a tensile plasticity comparable to that of the CG substrate and can sustain a tensile true strain exceeding 100% without cracking. A mechanically driven grain boundary migration process with a substantial concomitant grain growth dominates plastic deformation of the gradient NG structure. The extraordinary intrinsic plasticity of gradient NG structures offers their potential for use as advanced coatings of bulk materials.

Synergetic strengthening far beyond rule of mixtures in gradient structured aluminum rod

“…Metals exhibiting gradient microstructures have recently become the focus of research for their remarkable ability to produce a superior combination of strength and ductility in metallic systems [1][2][3]. Gradient structures can be defined as microstructures with macroscopic gradients in one or a combination of the several types of microstructural features including, but not limited to, grain size [1][2][3][4][5][7][8][9], texture [4], dislocation density, twin density [6], precipitates, etc.…”

“…Gradient structures can be defined as microstructures with macroscopic gradients in one or a combination of the several types of microstructural features including, but not limited to, grain size [1][2][3][4][5][7][8][9], texture [4], dislocation density, twin density [6], precipitates, etc. The most common and well studied gradient structure is grain size gradient structure [1][2][3][4][5], which often consist of nanocrystalline or ultrafine grains at the surface of a tensile sample, which gradually transition to coarse grains in the interior over distances of~50 μm or longer.…”

“…Gradient structures can be defined as microstructures with macroscopic gradients in one or a combination of the several types of microstructural features including, but not limited to, grain size [1][2][3][4][5][7][8][9], texture [4], dislocation density, twin density [6], precipitates, etc. The most common and well studied gradient structure is grain size gradient structure [1][2][3][4][5], which often consist of nanocrystalline or ultrafine grains at the surface of a tensile sample, which gradually transition to coarse grains in the interior over distances of~50 μm or longer. Although the means by which gradient microstructures can be created include Surface Mechanical Grinding Treatment, Surface Mechanical Attrition Treatment (SMAT), Ultrasonic Shot Peening [11], Wire Brushing [12], and Air Blast Shot Peening [13], most of the seminal work was undertaken with SMAT [1,10,12,[14][15][16].…”

Ductile-Phase Toughening in TiBw/Ti-Ti3Al Metallic-Intermetallic Laminate Composites

“…From these results, we conclude that deformation in the TiTi 3 Al laminated composite should be more easily activated because of stress redistribution in the laminated architecture, which aligns with experimental measurements (a greater elongation in Figures 3 and 4). [16,17,19] The high strain regions in the Ti-Ti 3 Al laminated composite occupy greater area than those in monolithic Ti 3 Al (Figures 5(a) and (b)). For instance, in monolithic Ti 3 Al (Figure 5(c)), only 33 pct of units contribute to a strain of >3.3 9 10 À4 , compared with 82 pct in the laminated composite.…”

“…Enhancement in fracture toughness results from the suppression of formation of an unstable major crack by stress redistribution and strain delocalization, and the composite thus seems to become insensitive to flaws especially in a submicron scale. [16,17] In the case of monolithic Ti 3 Al, the onset of cracking is a primary means for stress relaxation, often contributing to a premature fracture. In laminated composites, when the notch tip locates in ductile TiB w /Ti layer, stress concentrations at the cusp are always relieved by means of plastic strain of Ti, thus making cracks hard to be produced and amplified.…”