In U.S. Patent 7,736,448, the Institute of Metal Research Chinese Academy of Sciences (Shenyang, CN) divulges a process for manufacturing nano icrystals copper (Cu) material with super high strength and conductivity. The nanocrystalline materials refer to single phase or multiphase solid materials consisting of very fine grains of 1-100 nm in diameter. Due to its small grain and numerous grain boundaries (GBs), nanocrystalline materials are expected to exhibit tremendous difference from conventional micron-sized polycrystalline materials in physical and chemical performances, such as mechanics, electrics, magnetics, optics, calorifics, chemistry, etc.
According to inventors Lei Lu, Xiao Si, Yongfeng Shen and Ke Lu the process yields a nanocrystalline metallic material, particularly a nano-twin copper material with ultrahigh strength and high electrical conductivity.
High-purity polycrystalline Cu material with a microstructure of roughly equiaxed submicron-sized grains (300-1000 nm) was produced by pulsed electrodeposition technique, by which high density of growth-in twins with nano-scale twin spacing were induced in the grains. Inside each grain, there are high densities of growth-in twin lamellae. The twin lamellae with the same orientations are inter-parallel, and the twin spacing ranges from several nanometers to 100 nm with a length of 100-500 nm.
FIG. 1-1 is a bright-field TEM image of the as-deposited copper with nano-scale twins by means of pulsed electrodeposition
This Cu material has more excellent performance than existing ones. The tensile yield strength and ultimate strength of the present Cu material at room-temperature can be as high as 900 MPa and 1086 MPa, respectively, and such a high tensile strength can not be achieved for the Cu materials with the same chemical composition prepared by any traditional methods. Meanwhile, the present Cu sample also keeps a good electrical conductivity, for example, the room-temperature resistivity is (1.75.+-.0.02).times.10.sup.-8 .OMEGA.m, corresponding to 96% IACS, which is close to that of the conventional coarse-grained Cu.
The preparation method of nano-twin Cu with ultrahigh tensile strength and high electrical conductivity is as follows:
Using electrodeposition technique, the electrolyte consists of electron purity grade CuSO4 solution with ion-exchanged water or distilled water, pH 0.5-1.5; anode is 99.99% pure Cu sheet; cathode is Fe or low carbon steel sheets plated with a Ni--P amorphous surface layer.
Detailed electrolysis technique parameters are as follows: pulsed current density is 40-100 A/cm.sup.2 with a on-time (t.sub.on) of 0.01-0.05 s and off-time (t.sub.off) of 1-3 s, the distance between cathode and anode of 50-150 mm, ratio of anode and cathode areas of (30-50).mu.l. The electrolyte was controlled with a temperature range from 15-30.degree. C., while be stirred electro-magnetically. The additive is composed of 0.02-0.2 mL/L gelatine (5-25%) aqueous solution and 0.2-1.0 mL/L high-purity NaCl (5-25%) aqueous solution.
The nano copper crystals have the following advantages:
1. Excellent property. One feature of present invention is that high density of growth-in twins with nano-meter spacing was induced in pure Cu specimens by means of pulsed electrodeposition techniques. The spacing of the twin lamellae varies from several nanometers to 100 nm, and the lengths are about 100-500 nm. The present material shows the ultrahigh tensile yield strength of 900 MPa at room temperature, which is much higher than that of the Cu samples with comparable grain size produced by conventional method. Meanwhile, the sample keeps a very good conductivity: the electrical conductivity at room-temperature is 96% ICAS.
2. Wide application. Because of the special twin lamellae with a nanometer space, the present Cu shows an ultrahigh strength, while maintaining reasonable electrical conductivity and thermal stability. Therefore, this special material sheds light on the rapidly developing computer industry, radio communication and printing board.
3. Simple preparation method. The Cu specimens with high density growth-in nano-scale twins can be achieved by means of the conventional electrodeposition technique by modifying the technological conditions and controlling appropriate deposition parameters.
Using electrodeposition technique, the electrolyte consists of electron purity grade CuSO4 solution with ion-exchanged water or distilled water, pH 0.5-1.5; anode is 99.99% pure Cu sheet; cathode is Fe or low carbon steel sheets plated with a Ni--P amorphous surface layer.
Detailed electrolysis technique parameters are as follows: pulsed current density is 40-100 A/cm.sup.2 with a on-time (t.sub.on) of 0.01-0.05 s and off-time (t.sub.off) of 1-3 s, the distance between cathode and anode of 50-150 mm, ratio of anode and cathode areas of (30-50).mu.l. The electrolyte was controlled with a temperature range from 15-30.degree. C., while be stirred electro-magnetically. The additive is composed of 0.02-0.2 mL/L gelatine (5-25%) aqueous solution and 0.2-1.0 mL/L high-purity NaCl (5-25%) aqueous solution.
The nano copper crystals have the following advantages:
1. Excellent property. One feature of present invention is that high density of growth-in twins with nano-meter spacing was induced in pure Cu specimens by means of pulsed electrodeposition techniques. The spacing of the twin lamellae varies from several nanometers to 100 nm, and the lengths are about 100-500 nm. The present material shows the ultrahigh tensile yield strength of 900 MPa at room temperature, which is much higher than that of the Cu samples with comparable grain size produced by conventional method. Meanwhile, the sample keeps a very good conductivity: the electrical conductivity at room-temperature is 96% ICAS.
2. Wide application. Because of the special twin lamellae with a nanometer space, the present Cu shows an ultrahigh strength, while maintaining reasonable electrical conductivity and thermal stability. Therefore, this special material sheds light on the rapidly developing computer industry, radio communication and printing board.
3. Simple preparation method. The Cu specimens with high density growth-in nano-scale twins can be achieved by means of the conventional electrodeposition technique by modifying the technological conditions and controlling appropriate deposition parameters.
FIG. 2-1 is the HRTEM image of the as-deposited copper with nano-scale twins by means of pulsed electrodeposition.
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