Sthty On Texture And Surface Finish Of Metal Substrate Used For The Second High Temperature Coated Conductor

YBCO coated conductors is a kind of functional material with wide application prospect and excellent performance. The high performance metal substrate is the basis for obtaining the coated conductor with high current carrying capacity. At present, the existing preparation process of the Ni-5at.%W(Ni5W) alloy substrates still need to be optimized for large-scale industrialization and the surface of the Ni5 W alloy substrates is not smooth enough to obtain high quality of buffer layer. The commercial Hastelloy C-276 alloy tape also has the problem on its surface quality, which is unable to coat the buffer layer. In view of the above problems, the strong cube textured Ni5 W alloy substrate with high surface quality has been obtained via optimizing the traditional preparation process, and then the LZO buffer layer has been deposited on the substrate in this thesis. Subsequently, the electrochemical polishing technology was used for smoothing the surface of Hastelloy C-276 alloy. The best parameters of the polishing process were determined, and the high flat surface of Hastelloy C-276 alloy was obtained. The original novelties of the thesis are described in details as follows.First of all, the optimized preparation process of the Ni5 W alloy substrates was improved by reducing the initial thickness and heat treatment temperature. The strong cube textured Ni5 W alloy substrate with cube texture fraction of 98.2%(<10o) was obtained after annealing at 1050 oC for 1 h. The full width half maximum(FWHM) values for the X-ray(111) ?-scan and the(002) ?-scan of this substrate were 5.84oand 4.76o, respectively. The cube texture evolution of Ni5 W alloy deformed up to a very high strain was thoroughly investigated during the process of deformation, recrystallization as well as grain growth. A typical copper-type rolling texture was obtained after heavy cold rolling. The fraction of rolling texture was slightly strengthened during recovery, and then strongly reduced during recrystallization process. The cube texture was formed by consuming the rolling texture components during the discontinuous recrystallization process. The cube grains have a size advantage with respect to the non-cube grains.The second, the electrochemical polishing method was used to smoother the surface of the strong cube texture in Ni5 W alloy substrate. The effect of the surface roughness of the Ni5 W alloy substrate on the quality of the epitaxial La2Zr2O7(LZO) buffer layer was investigated. The results indicated that the surface roughness is smaller, the cube texture fraction of the La2Zr2O7(LZO) buffer layer is higher. Furthermore, after polishing the strong cube textured Ni5 W alloy substrates using chemical solution method, the well epitaxial LZO buffer layer with a smooth, continuous and crack-free morphology was obtained. The fraction of {001}<110> orientation the epitaxially grown LZO buffer layer was 97.2%(<10o), and the FWHM values of(111) ?-scan and(002) ?-scan were 5.22oand 5.0o, respectively.Then, the electrochemical polishing method was used on smooth treatment of the surface of Hastelloy C-276 alloy substrate. The typical curve of activation-passivatio-passivation of polarization was obtained, and the mechanism of electrochemical polishing combined with the passivation membrane theory was clarified. The effect of parameters of electrochemical polishing(such as electrolytic polishing temperature, polishing time and polishing distance) on the surface roughness of substrate were investigated. The optimized parameters of electrochemical polishing process were obtained by orthogonal experiment. The surface roughness(Ra) < 1 nm(5 ?m×5 ?m) and root mean square average(Rq)<1 nm(5 ?m×5 ?m) were obtained, which show a high bright and clean surface in the Hastelloy C- 276 alloy surface flat and level.Finally, a continuous dynamic electrochemical polishing test line was designed and built, and a continuous surface roughness measurement technique was also developed on the atomic force microscope(AFM). The surface leveling treatment of the 10 m long-length Hastelloy C- 276 tape was realized via optimizing the parameters of the electrochemical polishing processing. The surface roughness(Ra) < 2 nm(5 ?m×5 ?m) and root mean square average(Rq)<2 nm(5 ?m×5 ?m) of the surface on the 10 m long Hastelloy C- 276 tapes were obtained. It indicated that the surface quality of the Hastelloy C- 276 alloy can satisfy to the IBAD technical route for preparing buffer layer.In summary, this thesis optimized the preparation process of the Ni5 W alloy substrates firstly, and studied the rolling texture formation and the mechanism of cube texture formation in the recrystallization process. Secondly, the influence between the surface roughness and the quality of the buffer layer is verified subsequently. These research works will greatly promote the industrialization process of Ni5 W alloy substrates. The surface roughness of the Hastelloy C-276 alloy substrates was systematically studied, and the precision control technology of the Hastelloy C-276 surface roughness. Finally, a continuous dynamic electrochemical polishing test line was built, and the surface leveling treatment of the 10 m long Hastelloy C-276 tap was realized. At the same time, desighed and developed a continuous surface roughness detection equipment base on the AFM. These research works have provided the equipment support and the experimental basis for the realization of the Hastelloy C-276 alloy substrate, and its research has great scientific significance and economic value.