Recrystallization and cube texture formation in heavily cold-rolled Ni7W alloy substrates for coated conductors
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The formation of deformation and recrystallization textures has been investigated in a Ni7W alloy after heavy cold rolling and subsequent annealing at different temperatures. Cold rolling to a von Mises strain of 4.17 produced a mix of rolling texture that lies between classical brass- and copper-type rolling textures, with the fraction of S({123},634.), brass({110},112.), and copper({112},111.) orientations being 33, 28, and 13%, respectively. The fraction of rolling texture for the deformed Ni7W alloy samples increased slightly during recovery, was then consumed significantly during recrystallization, and dropped to 22% after being annealed at 800 °C for 1 h. The fraction of cube({001},100.) orientation increased to 26% after primary recrystallization, whereas other random orientations of 43% formed in the Ni7W alloy samples. Further annealing promoted cube grain growth, which lead to a significant strengthening of the cube texture and to a significant loss in high angle boundary (HAB). The fractions of cube texture and HAB of the Ni7W alloy substrate were 92.1 and 27.8%, respectively, after annealing at 1200 °C for 1 h.
I. INTRODUCTION
High Tc superconducting tapes based on YBa2Cu3O7 d (YBCO) consist of an epitaxial superconducting layer grown on textured metal substrates.1,2 In the rolling assisted biaxially textured substrate (RABiTS) technique, the substrate with a strong cube {001},100. texture and minimal high angle boundaries (HABs) can be obtained by heavy cold rolling and subsequent annealing. The cube texture is transferred via buffer layers to the YBCO film through epitaxial growth and results in a low angle boundary (LAB) in the superconducting layer.3–5 Ni–W alloys are promising substrate materials for coated conductors.6–8 Ni5W alloy substrates form strong cube textures (.97%) after heavy rolling and subsequent high temperature annealing. One drawback of the Ni–W material is its comparatively high Curie temperature that results in high energy losses in superconducting tapes used in alternating current applications at typical operating temperatures (;77 K).9,10 Increasing the tungsten content can suppress ferromagnetism and improve NiW alloy mechanical strength.11 Optimized treatment conditions are necessary to improve the texture quality in highly alloyed NiW alloy substrates since the stacking fault energy (SFE) decreases as the tungsten content increases, as for example in Ni7W and
Ni9W.12 Recently, a strong cube texture was obtained in Ni7W alloy substrates by intermediate and two-step annealing.13,14 However, previous studies of RABiTS-processed Ni7W alloy substrates focused mostly on microstructures and textures produced by high-temperature annealing, with little effort to characterize the formation of deformation and recrystallization textures. To enable a systematic comparative study, the evolution of deformation and recrystallization textures and the formation of a strong cube texture in the Ni7W alloy substrates are investigated in this work using four circle x-ray diffraction (XRD) and elec
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