Mangmang Gao

Fabrication of the Textured Ni-9.3at.%W Alloy Substrate for Coated Conductors

It is difficult to obtain a sharp cube texture in the Ni-9.3at.% W substrate used for coated conductors due to its low stacking fault energy. In this paper, the traditional cold rolling procedure was optimized by introducing an intermediate recovery annealing. The deformation texture has been improved after three recovery annealing cycles at 500°C for 2 h during the cold rolling process. After optimized recrystallization annealing, a Ni-9.3at.% substrate with a cube texture content of 87.7% (<;10°) has been obtained. The effect of the intermediate annealing on cube texture formation is attributed to the improved deformation texture and to the enhanced pre-existing cube oriented structure in the deformed matrix.

Preparation of

CeO₂ caped La₂Zr₂O₇ (LZO) buffer layers on cube-textured Ni5W substrates were fabricated by the method of chemical solution deposition(CSD). The orientation of both LZO film and CeO₂/LZO buffer layer was investigated using conventional XRD and X-ray four circle diffractometers, respectively. The results reveal that both the LZO film on Ni5W substrates and CeO₂ film on LZO buffer layer are grown epitaxially. The value of Full Width at Half Maximum (FWHM) of (111) Phi scan of CeO₂/LZO buffer layer is around 8^deg, and the FWHM of (200) omega-scan of CeO₂/La₂Zr₂O₇ buffer layer is 6.5^deg, indicating a good in-plan orientation of the as obtained buffer layers. It was observed by the high resolution SEM that the surface of LZO buffer layer is crack-free and very dense. The surface result observed by AFM indicates a very smooth CeO₂ surface with 5.9 nm of the root mean square roughness measured in an areas of 30 times 30 mum². AES depth profile results of CeO₂/LZO buffer layers shows that the deposited LZO film could effectively prevent the diffusion of Ni into the buffer layer.

{\rm CeO}_{2}/{\rm La}_{2}{\rm Zr}_{2}{\rm O}_{7}

Thin, reinforced and biaxially textured Ni5W/Ni12W/Ni5W composite substrate for coated conductor applications has been fabricated by traditional powder metallurgy method using the sparking plasma sintering (SPS) technology, followed by cold rolling and annealing. In-situ EBSD strain-stress analysis shows that the yield stress (δ0.2) can reach 240MPa. The high quality of cubic texture and boundaries of low misorientation angle were stable until elongations as high as 2%. Meanwhile, the cubic grain fractions on surfaces of top Ni5W layer of the composite tapes are 98.3%, 99.5% and 99.8%, respectively, corresponding to be annealed at 1250°C for 60min, 120min and 180min, indicating the cube texture can successfully sustain after severe treatment condition.

Buffer Layers on Textured Ni5W Substrates by Chemical Solution Deposition Method

It is considered as a challenge for RABiTS route to get cube textured Ni-W alloy substrates with high mechanical and magnetic properties for coated conductors. The works of our group in recent years are summarized about different Ni-W substrates with high W content and composite tapes made by RABiTS technique. The fabrication process and the mechanism of cube texture formation in above different tapes are studied systematically. Compared with commercial Ni-5 at.%W substrate, these alloy substrates show a comparable texture quality and improved mechanical properties as well as reduced or zero magnetization especially in the novel composite substrates.

Stable cube texture in an advanced Ni alloy composite substrate prepared by powder metallurgic method

The improvement of mechanical and magnetic properties of textured NiW alloy tapes are considered as a main challenge for RABiTS substrates in coated conductors. The present paper summaries the successful development of several textured NiW substrate tapes with high W contents as well as advanced NiW composite substrates with high strength and reduced magnetization. The fabrication processes of these tapes and their characterizations are presented in detail. The results on the texture quality and mechanical properties as well as on the magnetic behaviors of these tapes are promising in view of the future application in coated conductor and constitute an alternative to the well known Ni5W RABiTS substrates.

Development of cube textured Ni-W alloy substrates used for coated conductors

Ni-12at.%V alloy is a promising candidate for non-magnetic cube textured metallic substrates used for high temperature coated conductors. In this work, a textured Ni-12at.%V substrate has been fabricated by powder metallurgy route. After cold rolling and recrystallization annealing, a cube texture content as high as 99% (<;10°) was obtained, and the low angle grain boundary fraction is 89%. In addition, the FWHM values of phi-scan and rocking curve are 7.77° and 7.37°, respectively. According to micro-hardness measurement, the HV value of Ni-12at.%V tape is three times higher than that of pure Ni and to a certain extent higher than that of Ni-5at.%W. Furthermore, the Curie temperature of the Ni-12at.%V substrate is decreased to less than 77 K due to the addition of vanadium element in Ni.