Intrinsic tensile plasticity and deformation mechanism of nanometals studied by metals
Recently, the Lu Ke research group of the Shenyang National Laboratory for Materials Science of the Institute of Metal Research, Chinese Academy of Sciences has made important breakthroughs in improving the plasticity and toughness of nanometals. They found that gradient nano (GNG) metallic copper has both extremely high yield strength and high tensile plastic deformation capacity. This excellent comprehensive performance with both high strength and high tensile plasticity has opened up a brand-new path for the development of high-performance engineering structural materials. The research results were published in the United States "Science" (Science) magazine (February 17 online).
The ideal properties of engineering structural materials are usually high strength and high toughness and plasticity, however, strength and toughness and plasticity are often not both. High-strength materials tend to have poor plasticity, while materials with good plasticity have low strength. Nano metal materials (that is, polycrystalline metals with a grain size in the nanometer scale) are a typical high-strength material, whose strength is an order of magnitude higher than that of ordinary metals, but they have almost no tensile plasticity. How to improve the plasticity and toughness of nano-metals has become a major scientific problem in the field of international materials in recent years.
Gradient nanostructure refers to the spatial distribution of grain size in a gradient. The Luke research group successfully prepared a gradient nanostructure on the surface of pure copper rods using surface mechanical grinding (SMGT). Crystal structure (grain size is tens of microns), the thickness of this gradient nanostructure can reach hundreds of microns. The gradient nanostructure layer has a very high tensile yield strength, and the yield strength of the outermost layer 50 μm thick gradient nanostructure is as high as 660 MPa (10 times that of coarse-grained copper). Room temperature tensile experiments show that the surface layer with gradient nanostructures remains intact without cracks when the true tensile strain is as high as 100%, indicating that its tensile plastic deformation ability is better than coarse-grained copper. This excellent plastic deformation ability stems from the unique deformation mechanism of the gradient nanostructure. Microstructure studies have shown that the dominant deformation mechanism of the gradient nanostructure during the stretching process is mechanically driven grain boundary migration, resulting in accompanying grain growth . This deformation mechanism is completely different from traditional material deformation mechanisms such as dislocation motion, twinning, grain boundary slippage, or creep.
Surface mechanical milling treatment is a new technology for preparing gradient nanostructures developed by Shenyang National Laboratory for Materials Science (CAS), Institute of Metal Research, Chinese Academy of Sciences in recent years. Its preparation process is simple and suitable for industrial applications. The development of this new technology not only promotes the basic properties of gradient nanometals, but also plays an important role in promoting the industrial application of high-performance gradient nano-surface materials and the development of material surface engineering technology.
Figure A is a longitudinal cross-section observation of the nano-gradient / coarse-crystalline sample after tensile fracture; Figure B is a scanning electron micrograph at position B (true strain 24%) in Figure A. Figures C and D are the EBSD images at position C (true strain 54%) and D (true strain 127%) in Figure A, respectively. Figure BD shows the growth of nano-grains after different tensile strains.
The basic properties of EVA material: shock resistance, heat insulation, moisture resistance, chemical corrosion resistance and other advantages, and do not absorb water. EVA rubber and plastic products are designed to be processed into various colors. Its shockproof performance is better than that of traditional packaging materials such as polystyrene (foam), and it meets environmental protection requirements, making it the choice for export products. Compared with the requirements of special product applications, it has fire-resistant (flame retardant) EVA products; due to the large difference in density, it can also have more uses.
Water resistance: closed cell structure, non-absorbent, moisture-proof, good water resistance.
Resistant to chemical corrosion such as seawater, grease, acid and alkali, antibacterial and odorless
Shock resistance: high resilience and tensile strength, strong toughness, good shock resistance and cushioning performance.
Thermal insulation: thermal insulation, thermal insulation and cold protection and low temperature performance, can be cold and exposed to the sun.
Sound insulation: closed cells, good sound insulation, effectively reduce the volume decibel.
Processability: easy to cut, punch, hot press, slit, form, glue, fit, pad and other processing.
Camera Bag,New Microfibre Camera Bag,Gopro Camera Storage Bag,Gopro Mini Storage Bag
Dongguan Junkai Packaging Products Co., Ltd , https://www.diystoragecase.com