Recently, a team of professor Cao Zhenhua from Nanjing University of Technology and others have developed new methods to simultaneously improve the strength, plasticity and conductivity of nanostructured metal materials. This new structural design can also be effectively extended to other metal systems. Related results were published in the Journal of Materials recently.
Metal materials usually have excellent strength, plasticity and electrical conductivity, but these three properties are mutually exclusive and difficult to achieve both. How to improve the three properties of metal materials at the same time and reduce the constraints between the performances has always been a research difficulty in the field of metal materials.
The research team used nano-metal copper as the research object, using the "bottom-up" method, that is, using DC magnetron sputtering technology to introduce an ultra-thin metal tantalum layer in the copper metal film, the size is close to the thickness of the grain boundary. To a role similar to "artificial grain boundaries". By adjusting the pitch of the tantalum layer, two layered metal composite thin films with gradient grains and equal-sized grains are obtained. The researchers used nano-indentation and in-situ compression to test the mechanical properties, and found that the yield strength and uniform plastic strain of the metal composite film reached 1 GPa and 70%, respectively.
The team worked with Nanjing University and Purdue University to design a nanostructured metal material with both high strength and high plasticity. At the same time, it was found that the gradient grain metal exhibited a linear strain hardening behavior with a hardening index of 1.
To further reveal the internal mechanism of material strengthening, Cao Zhenhua studied the plastic deformation process with large-scale molecular dynamics simulation. Since the surface of the metal film has a large grain size, about 280 nm, which is much larger than the free path of electron scattering of metal copper (39 nm), it can be predicted that the surface of the film has good conductivity. (Reporter Wen Caifei Correspondent Zhang Xiaoqing)
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