Wang Yinmin, Li Ju, Hamza Alex V, Barbee Troy W
Nanoscale Synthesis and Characterization Laboratory, Chemistry, Materials, and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA.
Proc Natl Acad Sci U S A. 2007 Jul 3;104(27):11155-60. doi: 10.1073/pnas.0702344104. Epub 2007 Jun 25.
It is known that the room-temperature plastic deformation of bulk metallic glasses is compromised by strain softening and shear localization, resulting in near-zero tensile ductility. The incorporation of metallic glasses into engineering materials, therefore, is often accompanied by complete brittleness or an apparent loss of useful tensile ductility. Here we report the observation of an exceptional tensile ductility in crystalline copper/copper-zirconium glass nanolaminates. These nanocrystalline-amorphous nanolaminates exhibit a high flow stress of 1.09 +/- 0.02 GPa, a nearly elastic-perfectly plastic behavior without necking, and a tensile elongation to failure of 13.8 +/- 1.7%, which is six to eight times higher than that typically observed in conventional crystalline-crystalline nanolaminates (<2%) and most other nanocrystalline materials. Transmission electron microscopy and atomistic simulations demonstrate that shear banding instability no longer afflicts the 5- to 10-nm-thick nanolaminate glassy layers during tensile deformation, which also act as high-capacity sinks for dislocations, enabling absorption of free volume and free energy transported by the dislocations; the amorphous-crystal interfaces exhibit unique inelastic shear (slip) transfer characteristics, fundamentally different from those of grain boundaries. Nanoscale metallic glass layers therefore may offer great benefits in engineering the plasticity of crystalline materials and opening new avenues for improving their strength and ductility.
众所周知，大块金属玻璃的室温塑性变形会受到应变软化和剪切局部化的影响，导致拉伸延展性几乎为零。因此，将金属玻璃纳入工程材料时，往往伴随着完全脆性或有用拉伸延展性的明显损失。在此，我们报告了在晶体铜/铜锆玻璃纳米层压板中观察到的异常拉伸延展性。这些纳米晶-非晶纳米层压板表现出1.09±0.02吉帕的高流动应力、几乎弹性-完全塑性的行为且无颈缩现象，以及13.8±1.7%的拉伸断裂伸长率，这比传统晶-晶纳米层压板（<2%）和大多数其他纳米晶材料中通常观察到的伸长率高六至八倍。透射电子显微镜和原子模拟表明，在拉伸变形过程中，剪切带失稳不再影响5至10纳米厚的纳米层状玻璃层，这些玻璃层还作为位错的高容量汇，能够吸收由位错传输的自由体积和自由能；非晶-晶体界面表现出独特的非弹性剪切（滑移）传递特性，与晶界的特性根本不同。因此，纳米级金属玻璃层可能在设计晶体材料的可塑性以及为提高其强度和延展性开辟新途径方面带来巨大益处。
