Recrystallization of Nickel and Ni Alloy Substrates for YBCO Coated Conductors

ABSTRACTTo 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.