Macroscopic tensile plasticity by scalarizating stress distribution in bulk metallic glass.

Meng Gao,Wei-Hua Wang,Jie Dong,Yong Tian Wang,Yong Huan

doi:10.1038/srep21929

Abstract

The macroscopic tensile plasticity of bulk metallic glasses (BMGs) is highly desirable for various engineering applications. However, upon yielding, plastic deformation of BMGs is highly localized into narrow shear bands and then leads to the “work softening” behaviors and subsequently catastrophic fracture, which is the major obstacle for their structural applications. Here we report that macroscopic tensile plasticity in BMG can be obtained by designing surface pore distribution using laser surface texturing. The surface pore array by design creates a complex stress field compared to the uniaxial tensile stress field of conventional glassy specimens, and the stress field scalarization induces the unusual tensile plasticity. By systematically analyzing fracture behaviors and finite element simulation, we show that the stress field scalarization can resist the main shear band propagation and promote the formation of larger plastic zones near the pores, which undertake the homogeneous tensile plasticity. These results might give enlightenment for understanding the deformation mechanism and for further improvement of the mechanical performance of metallic glasses.

Highlights

It is possible for the viscosity of the whole Bulk metallic glasses (BMGs) decreases and approaches the liquid-like state under certain applied stress mode, which leads to the near-homogeneous deformation in BMGs
It is noted that the laser surface texturing treatment (LSTT) samples are different from those of the laser-ablation surface layer in previous research[41] and the depth of the laser-heating influenced layer is only several hundred nanometers for metals considering the ultrashort laser interaction time (10 fs)[42]
We selectively designed the laser texturing pore pattern on the surface and the shape of the pores were specially designed to the near-cylindrical profile [Fig. 1(f)] to systematically analyze the stress field distribution near the pores by finite element simulation

Summary

Introduction

Many experimental results imply that BMGs are not completely homogeneous in nanoscale, and there exists a lot of dynamic or property defects of flow units ( termed as liquid-like zones or nanoscale SBs)[32,33,34]. The stress, which is equivalent to temperature, plays a similar effect on the viscosity, and the yielding could be considered as a stress-induced glass transition[38] It is possible for the viscosity of the whole BMG decreases and approaches the liquid-like state under certain applied stress mode, which leads to the near-homogeneous deformation in BMGs. The surface artificial defects such as the notch, the indentation printing and the laser shock peening have been verified to induce the stress concentration, which could be used to induce a complex stress field. A strategy of stress distribution scalarization is proposed to enhance the macroscopic tensile plasticity of BMGs

Methods

Results

Conclusion