Study On The Ni-9.3at.%w Alloy Substrates Used For Coated Conductors

The second generation HTS tapes YBa₂Cu₃O_7-??YBCO? have excellent superconducting properties and potential price advantage, thus they become the focus of industrial application worldwide. With the development of rolling assisted biaxially textured subatrate?RABi TS? technology, large-scale application of substrates for coated conductors will be gradually put on the agenda. However, the mechanical and magnetic properties of commercial Ni-5at.%W?Ni5W? alloy substrates could not meet the needs of production and application, but high-strength and non-ferromagnetism Ni-9.3at.%W?Ni9.3W? alloy substrates are difficult to get strong cube texture due its low stacking fault energy due to that the dislocation slipping is blocked easily during rolling deformation process. Therefore, how to obtain a strong cube-texture in Ni9.3W alloy substrate has been a huge challenge. To solve this problem, this thesis carried out the study on the formation of cube texture in Ni9.3W alloy substrates used for coated conductors. Initial ingot was prepared by vacuum induction melting technology, Ni9.3W substrates of high cube texture content were fabricated through the static recovery technology and combining technology of static and dynamic recovery, respectively. Innovative research results are obtained as follows:Influence of refining grain size by deformation control and lubrication rolling on the cube texture formation in Ni9.3W alloy substrate was analysised by optical microscope?OM?, X-ray diffraction?XRD? and electron backscattered diffraction?EBSD? techniques. It was shown that the method of deformation refinement can effectively decrease the grain size of Ni9.3W alloy ingot after homogenized annealing. The cube texture content increases by 9.8% higher than that of without deformation refinement in Ni9.3W alloy substrate. Furthermore, the cube texture content increases 24.7% by adding total rolling deformation after decreasing grain size. According to these results, the parameters for preparation of the initial ingot are determined. On the basis of it, the influence of lubrication rolling on cube texture formation was also studied by comparing with that without lubrication rolling. Cube texture content with lubrication rolling is 2.5% higher than that of without lubrication rolling. In addition, the twin boundary??3? quantity and low angle grain boundary?LAGB? content by lubrication rolling is superior to that of without lubrication rolling, which illustrates that lubrication rolling has a significant effect on the cube texture formation.The effects of deformation sequences between static recoveries on the cube texture formation in Ni9.3W alloy substrates were studied in this thesis. The results show that rising gradient deformation sequence is an advantageous way to obtain a higher amount of cube texture, its content increases by 29.2% compared to that of traditional deformation sequence. On the basis of it, the effect of the new recrystallization annealing process on the cube texture formation was analysed. Two step anneals could effectively improve the cube texture content, which could further be enhanced by extending suitable holding time during the first step anneal. Finally, Ni9.3W alloy substrate with a cube texture content of ⁹0%?<15°? was obtained by optimized two step anneals, and its LAGB and ?3 contents are superior, being 72.3% and 11.1% respectively.Ni9.3W alloy substrates were prepared by an innovative technology, in which the dynamic and static recoveries was used together The optimized dynamic recovery temperature of 550°C was determined by analysis of cube texture content of Ni9.3W alloy substrates. Texture formation process was studied under the technology route. The rolling texture intensities were gradually increased with the increase of deformation reduction, and the intensities of Brass and S orientations showed a trend of rapid growth, then the Brass and S rolling orientations twere mainly formed. For recrystallization texture, with the increase of annealing temperature, the content of cube orientation showed a gradual upward trend, and the content of S and Brass orientations significantly decreased, but the content of Goss and Copper orientations showed a fluctuant changes. The total amount of rolling textures were significantly reduced, but they didn't fully converted to the cube texture. Conversely, the content of other orientations showed a significant increase, which indicates that recrystallization process of Ni9.3W substrates has a characteristic of continuous recrystallization. Ni9.3W alloy substrates with a cube texture content of 78.7%?<15°? were obtained by optimized two step anneals. Cube texture content increases by 38.7% compared to that of traditional rolling process.In summary, this thesis puts forward effective solutions and technology routes for low SFE Ni9.3W alloy in which it is difficult to obtain a high content of cube texture. Firstly, many factors in RABi TS technology were systematically studied in our work, such as deformation refinement grain, rolling lubrication, deformation sequence and recrystallization annealing. The cube texture of Ni9.3W substrates is effectively optimized and improved. Secondly, this thesis puts forward an innovative combination technology of static and dynamic recovery for Ni9.3W alloy substrates. In addition, the temperature of dynamic recovery, the process of texture formation as well as the recrystallization annealing were systematicly studied, which provides an experimental and theoretical basises for the future applications. Finally, all experimental works and datas obtained in Ni9.3W substrate in this thesis will provide an effective reference for preparing Ni9.3W susbtrates with sharp cube texture in the future.