THERMO-MECHANICAL PROCESSING OF NIOBIUM TITANIUM BASED SUPERCONDUCTORS

DUCTILE NIOBIUM TITANIUM (NBTI) ALLOY CONTINUES TO BE THE CHOICE MATERIAL FOR MOST OF THE LARGE SCALE SUPERCONDUCTIVITY DEVICES. THE PRESENT PROCESSING TECHNOLOGY FOR NBTI SUPERCONDUCTORS INVOLVES WORKING THE COMPOSITE IN SEVERAL STAGES WITH INTERMEDIATE HEAT TREATMENTS TO SUCCESSIVELY INCREASE THE AMOUNT OF ALPHA TITANIUM PRECIPITATE. THE EFFECT OF THE COMPLEX SET OF POSSIBLE HEAT TREATMENT CONDITIONS IS REASONABLY WELL UNDERSTOOD. IT IS GENERALLY TRUE THAT A HIGH CURRENT DENSITY (JC) CAN BE ACHIEVED BY INCREASING THE NUMBER AND LENGTH OF HEAT TREATMENTS. HOWEVER, STRAIN SPACE AVAILABLE FOR MULTIFILAMENT COMPOSITES AFTER THE LAST HOT EXTRUSIN IS SMALL, LIMITING THE NUMBER OF HEAT TREATMENTS. FURTHERMORE, THE INCREASED NUMBER OF HEAT TREATMENTS ADDS PROCESSING COST AND TIME. IT HAS ALSO BEEN OBSERVED THROUGH MICROSCOPY THAT THE COLD-WORK/HEAT TREATMENT CYCLES RESULT IN A NON-UNIFORM DEFORMATION OF NBTI GRAIN STRUCTURE WHICH IN TURN LEADS TO UNEVEN PRECIPITATION OF ALPHA PHASE WITHIN THE NBTI BETA GRAIN STRUCTURE. THIS PROJECT WILL INVESTIGATE A PROCESSING CONCEPT THAT IS NOVEL TO THE NBTI TECHNOLOGY. BASED ON THERMO-MECHANICAL PROCESSING (TMP), IT HAS THE POTENTIAL OF ACHIEVING A MORE UNIFORM DISTRIBUTION OF PRECIPITATES IN HIGHER VOLUMES AND, THEREFORE, HIGHER JC THAN THE CONVENTIONAL COLD-WORK/HEAT TREATMENTS ARE CAPABLE OF. THE PHASE I PROJECT WILL INVESTIGATE THE FEASIBILITY OF THE TMP APPROACH USING RUDIMENTARY MONOFILAMENT AND MULTIFILAMENTARY COMPOSITES, AND WILL EVALUATE THE RESULTANT MICROSTRUCTURE AND SUPERCONDUCTING PROPERTIES. IF PROVEN SUCCESSFUL THE TMP WILL REPLACE MOST IF NOT ALL IN-PROCESS LONG-TERM HEAT TREATMENTS AND WILL OFFER AN ECONOMICAL AND HIGH RATE PRODUCTION TECHNOLOGY.