Fabrication of Niobium sheet for RF cavities
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This thesis investigated the microstructure and mechanical property of RRR( high purity) and RG (low purity) niobium (Nb) sheet material. RRR Nb is used in the fabrication RF cavities. Our method involves processing bulk niobium by equal channel angular extrusion (ECAE) and then cross rolling to obtain sheets. This work is a study of the effect different thermomechanical processing variables have on the microstructure niobium sheets. Recrystallization behaviors strongly depended on the purity levels. Tensile tests on sheets clearly indicated the anisotropy in the sheet material. The ductility of the sheet was found to be the largest at an angle of 45o to the rolling direction. There was no apparent relationship observed in the yielding behavior in the different samples. The formability of the sheet measured by the anisotropy ratio suggested a strong dependence of anisotropy on texture. Texture results obtained show that different routes of ECAE can lead to variety of textures in final sheet material. Correlations between the microstructure and the ECAE routes suggest that effective control of microstructure is possible by the thermomechanical steps followed in this study.