ADDITION OF SILICON TO THE COPPER BETWEEN NIOBIUM-TITANIUM FILAMENTS TO REDUCE INTERDIFFUSION

IT HAS BEEN SUGGESTED RECENTLY THAT A THICK INTERFILAMENT BARRIER IS REQUIRED IN CONDUCTORS FOR THE SUPERCONDUCTING SUPER COLLIDER (SSC) BECAUSE THE FILAMENTS ARE RELATIVELY FINE AND BECAUSE LENGTHY, HIGH TEMPERATURE HEAT TREATMENTS ARE USED TO ACHIEVE THE HIGHEST CRITICAL CURRENT DENSITIES (JCS). THE NIOBIUM (NB) BARRIER THICKNESS WAS INTRODUCED IN EARLY SSC CONDUCTORS TO PREVENT INTERACTION BETWEEN COPPER (CU) AND THE NIOBIUM-TITANIUM (NBTI) FILAMENTS. AS MORE AGGRESSIVE HEAT TREATMENTS WERE EMPLOYED AND FILAMENT SIZES WERE REDUCED, THE THICKNESS OF THIS BARRIER BECAME INADEQUATE AND BOTH COPPER AND TITANIUM DIFFUSED THROUGH THE BARRIER. THE SUGGESTED SOLUTION TO THE PROBLEM WAS TO THICKEN THE BARRIER, BUT THIS, IF CARRIED TO THE EXTREME, HAD AN ADVERSE EFFECT ON THE OVERALL JC. RECENTLY, IN WORK DIRECTED PRIMARILY TOWARDS THE DEVELOPMENT OF MATERIALS FOR ALTERNATING CURRENT APPLICATIONS, IT HAS BEEN REPORTED THAT WHEN SILICON IS ADDED TO THE COPPER MATRIX, THE INTERDIFFUSION CAN BE GREATLY REDUCED. THE USE OF THIS APPROACH IN ADVANCED MATERIALS FOR THE SSC AND OTHER ACCELERATOR MAGNETS MAY REDUCE THE NECESSITY FOR THICK BARRIERS, REDUCE THE VOLUME OF INERT MATERIAL, AND INCREASE OVERALL JC. PHASE I IS CONCERNED WITH EXPLORING THE EXTENT TO WHICH SILICON CAN REDUCE THE INTERACTION BETWEEN CU AND NBTI. TWO TRIAL BILLETS ARE BEING PREPARED FROM NBTI MONOFILAMENTS WITHOUT A BARRIER: ONE BILLET WITH A CU MATRIX AND THE OTHER WITH A CU-2.5 WT.% SI MATRIX. A BASELINE WITH A CU MATRIX AND BARRIER CLAD NBTI IS ALSO BEING PREPARED FOR COMPARSION PURPOSES. THE EXTENT OF THE INTERACTION IS DETERMINED BY EXAMINING THE INTERFACE AND MEASURING THE ELECTRICAL PROPERTIES. IN PHASE II, SCALE-UP TO FULL-SIZED SSC BILLETS WILL BE EXPLORED AFTER THE OPTIMUM MATRIX COMPOSITION AND BARRIER THICKNESS-IF A BARRIER IS NECESSARY-HAVE BEEN DETERMINED.