L. Ma

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.

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

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.

A novel approach using powder metallurgy for strengthened RABiTS composite substrates for coated superconductors

We report on the development of mechanically strengthened, highly textured Ni–5 at.%W/Ni–12 at.%W composite materials prepared by a powder metallurgical approach as promising weakly magnetic substrates for coated superconductors. The key configuration of this composite substrate consists of a thin, sharp cubic textured Ni–5 at.%W layer on a Ni–12 at.%W alloy core, thus providing a mechanical reinforcement while decreasing the saturation magnetization of the whole substrate. The composite substrates have a sharp cubic texture at the top Ni–5 at.%W outer layer and their yield strength reaches 272 MPa, exceeding that of the commercially used Ni5W substrates by a factor of 1.6. The saturation magnetization of the composite substrate Ni5W/Ni12W/Ni5W is substantially reduced when compared to that of pure Ni and Ni–5 at.%W substrates, respectively.

Study on Fabrication of Ni-5 at.%W Tapes for Coated Conductors from Cylinder Ingots

Ni-5 at.%W (Ni5W) tapes with a strong cube texture were fabricated using the RABiTS technique and by starting from cylindrical shaped ingots. In contrast to a conventional cuboid-shaped ingot, a cylinder shaped ingot has no anisotropy along the axial direction and the resulting tape will therefore, during heavy cold rolling, be characterized by a lower concentration of stress along the edges of the ingot. It can reduce fabrication costs and increase process efficiency. The fraction of cube texture on the surface of the finally recrystallized tapes was investigated using the EBSD technique. It was observed that the fraction of cube texture within 10° from the ideal {001}〈100〉 orientation was ~98% and the fraction of LAGBs was ~90%. The as-obtained tapes have a strong cube texture also very close to the edge of the tape and they would therefore increase the fraction of applicable material while simplifying the heavy rolling process. Accordingly, it suggests that this fabrication method is a good choice to most small scale research laboratories for achieving long length Ni5W tapes for coated conductors with an easy way and a higher fraction of applicable material.

Fabrication of YBCO Films on

In this paper, we presented the results of YBCO films deposited epitaxially on both SrTiO3 single crystal and textured Ag substrates by a TFA-MOD method. The growing conditions and forming mechanisms of the YBCO films on these two kinds of substrates was investigated systematically. It was found that the precursor film coated on Ag substrate took less time to completely decompose to an amorphous precursor film during the first stage of the calcination than that on SrTiO3 substrate. Moreover, the higher temperature was needed to obtain pure YBCO phase on Ag substrate during the second annealing stage. A possible growing mechanism for this difference was described. A transport jc value of 1.5 x 104 A/cm2 (at 77 K) was obtained for the YBCO film deposited on Ag substrate, while the film on SrTiO3 substrate exhibited an a Tc onset of 92 K and a high jc value of 2.3 MA/cm2 at 77 K in self-field was measured.

{\rm SrTiO}_{3}

The YBCO films were directly deposited on cold-rolled Ag substrates by MOD (metal-organic deposition) method. The formation of YBCO phase and change of Ag textures were studied during firing precursor films. It was found that YBCO phase starts to be formed at 800°C when Ag {110} texture (most suitable texture for YBCO epitaxial growth) appears. With the increase of firing temperature, pure YBCO phase is obtained and Ag {110} texture gradually becomes stronger. The textures of both {110} texture in Ag substrate and biaxial orientation in YBCO film were optimized after holding the film at 900°C for 30 minutes. Finally, the YBCO film deposited directly on cold rolled Ag substrate has a good biaxial texture, a smooth and dense surface as well as high critical current density of 1.5×104A/cm2. The results show that cold-rolled Ag can be used as a substrate material to directly deposit YBCO film without any buffer layers by MOD method.

and Textured Ag Substrates by TFA-MOD Method

Mechanically strengthened, highly cube textured Ni-7at.%W/Ni-12at.%W multi-layer substrates used for coated conductors have been prepared by advanced spark plasma sintering technique. The key innovation for developing this weakly magnetic and reinforced substrate was to use a new powder metallurgy and sintering route to bond multi-layers of Ni7W-Ni12W-Ni7W together in order to get an initial ingot, then followed by optimized cold working and annealing. Particular efforts were made in view of the optimization of the design, pressing as well as the heat treatment processes of the starting ingots in order to obtain a chemically gradient composite bulk, thus ensuring the subsequent cold deformation of the bulk. The produced composite substrates have a strong {100} texture on the top Ni7W outer layer determined by EBSD and X-ray. The percentage of the biaxially orientated grains within a misorientation angle of 10° is as high as 97.5%, while the length percentage of low angle GBs ranging from 2° to 10° in the composite substrate reaches 87.2%. Moreover, the yield strength σ0.2 of the tape approaches 333 MPa, and the saturation magnetization is substantially reduced by 81.6% at 77K when compared to that of a commercial used Ni5W substrate.

Study on the formation of YBCO phase and texture transformation of Ag substrate during the heat treatment of TFA-MOD process

Long lengths of in-situ SiC doped MgB2/Fe mono- filamentary wires with high critical current densities and 7- filamentary MgB2/Nb/Cu/Fe wires with better thermal stability have been fabricated by either continuous tube forming & filling (CTFF) technique or combining both powder in tube (PIT) and CTFF process, respectively. Particular efforts were made in view of the optimization of the manufacturing and annealing processes of the wires. The as obtained wires were sintered under a vacuum furnace at different sintering temperatures and the optimized sintering of the MgB2 wires were investigated by the analysis of optical microscope, XRD, SEM, and the transport Jc measurements. The Jc value in a 8 at.% SiC doped MgB2/Fe mono- filamentary wire is more than 104A/cm2 at 4.2 K and a field of 11 T. While in doped 7- filamentary wire, the similar Jc value (104A/cm2) is obtained at 4.2 K and a field of 7.5 T. Moreover, the n factors are determined to be 33 and 10 at 11 T in the mono- and 7- filamentary MgB2wires with SiC doping, respectively, indicating the possibility to use the as fabricated MgB2 wires in the persistent mode for fields from 0.5 T to 10 T at 4.2 K.