Metal materials usually have excellent strength, plasticity and electrical conductivity, but it is well known that these three properties are mutually exclusive, like fish and bear paws, it is difficult to have both. "Professor Cao Zhenhua from the School of Materials Science and Engineering, Nanjing University of Technology said. How to improve the three properties of metal materials at the same time and reduce the constraints on performance has always been a research difficulty in the field of metal materials. Recently, the team of Cao Zhenhua has developed new The method can simultaneously improve the strength, plasticity and conductivity of nanostructured metal materials. This new structural design can also be effectively extended to other metal systems.
Metal materials are widely used in marine, aerospace, construction, automotive, and microelectronics fields, and are important basic materials for industrial development. In the application of metal, whether it is strength or plasticity, if it does not meet the requirements, it may cause accidents. For example, the bridge built is easy to break, the shock absorption function of the car is greatly reduced, and precision instruments such as computers and mobile phones are prone to crashes and cards. Such as the situation… The "universal" scientific problem of the "inverted relationship" between strength and plasticity in metal materials also exists in nanostructured metals. As the grain size or geometric size of the metal material decreases to the micro-nano scale, the strength of the nano metal is significantly improved. Due to the constraints of the nano-scale space, it lacks strain hardening ability and the plasticity decreases.
Nano metal film is one of the main component materials of microelectronic devices and microelectromechanical systems of mobile phone chips, computer CPUs. It designs and prepares high-strength and high-plasticity nanometals, and establishes new theories and methods of micro-nanomaterial performance variation. Information, The basis for the development of electronics and nanotechnology. "Because of the continuous breakthroughs in ultra-deep submicron processing technology, electronic components have been continuously miniaturized according to Moore’s law, and the miniaturization and intelligentization of mobile phones and computers have been gradually achieved. The metal Cu used in the new generation of microelectronic devices The characteristic size of important interconnected materials is also reduced to below 10nm, which results in significant changes in their mechanical properties that will affect the performance and operating life of microelectronics and microdevices." Cao Zhenhua added.
"We take nano-metal Cu as the research object and use the'bottom-up' method, that is, using DC magnetron sputtering technology to introduce an ultra-thin metal Ta layer in the metal Cu film, the size is approximately equal to the thickness of the grain boundary, starting from To the effect similar to'artificial grain boundary'." Cao Zhenhua said while sharing his scientific research ideas, "By adjusting the spacing of the Ta layer, two layered metal composites with gradient grains and equal-sized grains are obtained The mechanical properties of the film were tested by nanoindentation and in-situ compression. The results showed that the yield strength and uniform plastic strain of the metal composite film reached 1GPa and 70%, respectively." The team of Cao Zhenhua cooperated with Nanjing University and Purdue University in the United States. , Successfully designed a nanostructured metal material with both high strength and high plasticity, and found that the gradient grain metal exhibited a linear strain hardening behavior with a hardening index of 1.
In order to further reveal the internal mechanism of material strengthening, Cao Zhenhua used large-scale molecular dynamics simulation to study its plastic deformation process. 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 the metal Cu (39 nm), it can be predicted that the film surface has good conductivity. According to reports, this new structural design can also be effectively extended to other metal systems, and it has also opened up new ideas for the design and preparation of high-performance nanometals.