Preparation And Surface Modification Study Of Ni5W Alloy Substrate For YBCO Coated Conductor

7, one of the2nd generation (2G) high temperature superconducting materials, exhibites great potential for the practical applications as cables and magnets due to their high inrreversible magnetic field, high in-field superconducting performance and low AC loss. Generally speaking, coated conductors are composited of four fundamental parts:metallic substrate, buffer layers, YBCO layer and protection layer. Metallic substrate is not only responsible for the mechanical strength of the CC tape, but also working as the texture template for the epitaxial growth of the buffer layers and YBCO layer. In order to supply the basis to prepare the highly textured and flawless YBCO layer, the rolling assisted biaxially textured substrates (RABiTS) technique was adopted to prepared the Ni-5at.%W(Ni5W) alloy substrate with sharp cube texture and good surface characteristics. The content is as follows:Ni5W ingots was obtained with the starting materials of the stoichiometric amount of nickel powder and tungsten powder by the powder metallurgy. A vacuum arc furnace melting process is applied after powder metallurgy, in order to reduce the inhomogenity and realize homogenization. Then the Ni5W alloy substrate with the thickness of80μm is fabricated by hot rolling, cold rolling and recrystallizing heat treatment. The effect of the deformations rate per pass and general deformations rate to the rolling texture of Ni5W alloy substrate is investigated The results showed that small pass reduction and big general deformations rate is beneficial for the further growth of the cube textured grains after recrystallization heat treatment. The effect of pass reduction to the cube texture is smaller than the general deformation. After the cold rolling with the per pass5%and general deformations rate98%, the high content of S texture and Copper texture was obtained. The low temperature pre-annealing before the high temperature is beneficial to release of internal force before recrystallization which promoted the nucleation of cube orientation graim. After a700℃,40min low temperature annealing before1200℃,0.65m/h continuous annealing, the percentage content of cube texture of the long length Ni5W substates can reach97.2%. But～100%high content cube texture can be obtained by both one-step annealing and two-step annealing for the static state heat treatment of Ni5W alloy substrate.Iin order to improve the surface quality of substrate, the investigation of the electropolishing and physicochemical modifications has been carried out, respectively. The effect of technological parameter to the surface roughness is discussed. With the technological parameter of current density1A·cm-2～1.3A·cm-2，temperature0℃～30℃, time30s～60s, sulfuric acid concentration8.76mol·L-1～14mol·L-1, the roughness of substrate decrease to less than5nm. Based on the investigates of the polishing products in different sulfuric acid concentrations, it is found that the mechanism of Ni5W alloy substrate in sulfuric acid is closer to the viscosity theory. The compact and viscous tungstic acid formed on the surface of substrate in the proper sulfuric acid concentration play an important role to the electropolishing. Therefore, by controlling the sulfuric acid concentration, the formation rate of the substance formed on the substrate can be controlled to the proper thickness which is benefit to the selective dissolution. The c (2×2)-S superstructure is benefit to the epitaxial growth of oxide layers. Two different sulfuration methods which is elemental sulfur sulfuration and (NH4)2S solution have been applied in our study. The EDS and XPS show that there is S element on the substrate with the coverage rate of0.5ML. Because of the decomposition of sulfide, the coverage rate is less than0.5ML after sulfuration by (NH4)2S solution. The effects of surface reconstructions to the preparation of La2Zr2O7(LZO) film by chemical solution deposition (CSD) are discussed. The results show that the c (2×2)-S superstructure is obviously benefit to the epitaxial growth of LZO film on the Ni5W alloy substrate. Neither of the two methods required the high vaccum enviorment as traditional sulfuration process.In the paper, a reel-to-reel recrystallizing heat treatment furnace and continuous electropolishing device are designed and manufactured. The Ni5W substrate with the length of100m was prepared in China firstly and the quality of cube texture and surface satisfied the requirements for epitaxial growth of buffer layers on the substrate.