Recrystallization of Nickel and Ni Alloy Substrates for YBCO Coated Conductors

Abstract

To avoid grain boundary grooving and abnormal grain growth during recrystallization of nickel and Ni alloy substrate tapes, the commonly used high recrystallization temperatures must be lowered.The development of the cube orientation is a nucleation-growth process. So the kinetics of the cube recristallization is strongly temperature dependent, and there is a very marked effect of the stacking fault energy (SFE) of the specific alloy on the activation energy. Concurrently with measurements of the formation kinetics of the cube orientation, the recrystallization texture of Ni (+99,99 wt.%), NiCr10 wt.% and NiMn10 wt.% tapes in dependence on the deformation history, the annealing temperature and time was investigated. Profile rolling to a rectangular rod, without further high temperature annealing, leads to a worse cube texture compared to round swaged rods with an in-plane 200 peak splitting. The increase of the recrystallization temperature and time sharpens the texture due to grain growth, limited by the occurrence of secondary recrystallization when a sample specific temperature is exceeded.In binary Ni alloys the commonly used alloying elements reduce the SFE. This favors the formation of recrystallization twins {122}<212> obstructing the oriented coating. In Mn alloyed tapes this effect is strongly pronounced. The tapes show a good cube texture, but also a high volume fraction of twins due to the low SFE. To suppress the twin formation we investigated ternary Ni based alloys with respect to possibly increased SFE and report first results.

Effects of Degree of Deformation and Deformation Temperature on Primary Recrystallization Textures in Polycrystalline Nickel

“…It is commonly accepted that a sharp cube recrystallization texture usually forms in materials with a large component of the copper-type rolling texture, in which the major components are S and C, whereas the cube texture does not form in materials with brass-type rolling texture, in which B is the major component. [22] Lu¨cke and Hirsch [23,24] suggested that cube grains have the best chance of growing because the cube orientation forms a 40 deg/<111> high mobility boundary with the major components of the deformation texture. For example, the S component best meets the condition to form 40 deg/<111> high mobility boundaries.…”

An EBSP study of directionally recrystallized cold-rolled nickel

“…Ignoring the energy differences of the different grain boundaries, their model predicts that cube grains with less than six grain boundaries shrink slowly, and non-cube grains with less than six boundaries shrink rapidly, while non-cube grains with more than six boundaries will grow swiftly. Initially, this leads to strengthening of the cube-texture as the small non-cube grains disappear, as has been observed experimentally in both high-purity nickel [16][17][18][19][20] and aluminum alloys [36]. The resulting microstructure has a few large noncube grains with high-mobility boundaries in a fine-grained, cube-oriented matrix.…”

“…It is worth noting that several studies have shown that a cube texture results from primary recrystallization of heavily cold-rolled, high-purity nickel [11][12][13][15][16][17][18][19][20][21][22]. The 90% thickness reduction used here is almost the minimum to obtain cube texture in primary recrystallization of nickel [20,21,22]. Therefore, weak cube textures were produced at all directional annealing speeds.…”

“…6b). These small grains have the cube texture expected after primary re- crystallization of heavily cold-rolled nickel [11][12][13][15][16][17][18][19][20][21][22] (see Fig. 6c 11>, respectively.…”

“…On the right, labeled (a-d) are higher magnified images from various positions on the specimen. mary recrystallization [11][12][13][15][16][17][18][19][20][21][22]. Since the temperature gradient in front of the hot zone is large, the temperature is not high enough for the primary recrystallization to be completed at 6 mm in front of the hot zone.…”