THE BONDING OF MOLYBDENUM-AND NIOBIUM-CLAD FUEL ELEMENTS

A solid-state bonding technique involving the use of gas pressure at elevated temperatures was utilized for the self-bonding of molybdenum and niobium. Bonding conditions and surface preparation as a function of the integrity of the bond achieved were evaluated for each material. Optimum self-bonding of niobium was achieved by bonding parameters of 2100 to 2300 deg F at 10,000 psi for 3 hr with surfaces which had been prepared by etching in a nitrichydrofluoric acid solution prior to bonding. The process as developed was used to prepare niobium- clad flat-plate- and rod-type fuel elements and flat-plate subassemblies. Niobium tubing was also fabricated by this technique. (Molyb denum self-bonding was most readily achieved by gaspressure bonding at temperatures of 2300 to 2600 deg F at 10,000 psi for periods of 3 hr. With these bonding conditions a number of different surface preparations were satisfactory. Directional ductility of the molybdenum was encountered after bonding and methods to eliminate this were evaluated. Cross rolling with respect to the original rolling direction was shown to improve the ductility of molybdenum-clad specimens. (auth