Production and Quality Control of High Homogeneity Niobium 47 Weight Percent Titanium for Accelerator Applications
Teledyne Wah Chang (TWC) has been a supplier of Nb based superconductors since 1960. An original producer of Nb50Zr, TWC switched to the production of Nb47Ti because of its superior ductility and the demand from customers. The material specified for all superconducting accelerator magnet projects since Fermilab’s Energy Doubler project and the Isabelle project at Brookhaven National Laboratory (BNL) has been High Homogeneity Nb 47wt.% Ti (HiHo NbTi). HiHo NbTi was developed at TWC as a response to customer demand after difficulties experienced in the development of wire for Fermilab and Isabelle. The presence of freckles in the alloy interfered with uniform alpha titanium precipitation and resulted in highly variable, low critical current density product1. Other methods of consolidation were attempted with good results but these had other problems such as niobium inclusions and chemical variation along the ingot length2. The process of consolidating niobium and Titanium to produce homogeneous Nb47Ti was refined at TWC in the early 1980’s to produce product with minimal freckling and consistent properties. Our HiHo NbTi has normal compositional variation from the dendritic structure formed as the material is cast and little or no evidence of the high titanium regions, commonly called freckles. The titanium has normal compositional fluctuations on the order of 1 weight percent. Freckles are small regions in which titanium content is 5 to 10 weight percent higher than the surrounding matrix. Freckles can be easily seen in radiographs of billet slices or seen in rod samples after proper polishing and etching. Verification of the HiHo grade is made by radiographic examination and comparison to standards of acceptability, but it is guaranteed by control of the process3.
KeywordsStatistical Process Control Brookhaven National Laboratory Titanium Sponge Filament Area Billet Diameter
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