NUCLEAR ENGINEERING AND DESIGN 3 (1 966) 365- 368. NORTH-HOLLAND PUBLISHING COMP ., AMSTERDAM DIFFUS ION BONDING OF ZIRCALOY-2 TO STEEL BY SWAGING * ** E. BRUTTO, G. PERONA, R. SESINI Laboratorio di Tecnologie , C. I. S. E., Segrate (Milano) , Italy G. VOLTA Servizio di Tecnologie, C.C.R. Euratom, Ispra (Varese), Italy Received 27 December 1965 A metallurgice,1 bond between zircaloy and steel has been obtained by hot swaging. This method, de- veloped at first on fiat specimens and then applied to tubular joints, gives diffusion layers having a very small thickness. Mechanical, thermal and corrosion tests on tubular joints 40 mm in diameter have given satisfactory results. The application of the process to larger joints is projected. I. INTR ODU CTION In order to obtain sound metallurgical joints between zircaloy and steel two ways can be used: cold processes (explosive welding [1] and ultra- sonic welding [2]) and plastic deformation pro- cesses (coextrusion [3], hot rolling [4], friction welding [5] and swaging). The first processes prevent the formation of brittle intermetallic compounds by limiting the temperature. However, up to the present not one of these processes has reached the stage of in- dustrial application. The processes of the second type reduce the formation of brittle intermetallic compounds by shortening the contact time at the temperature required for the achievement of the metallurgi- cal bond. The metal surfaces are sheared past each other so that oxides or other films are broken and uncontaminated materials come into contact providing a great quantity of diffusion nuclei. The main advantage of the swaging process presented in this paper is that it is suitable for application to long tubes in the finished state. The standard conditions (temperature, area re- duction ratio, surface treatment, etc.) for bond- ing zircaloy to steel by swaging have been studied on flat specimens using a pneumatic hammer. Later they were adapted for the fabri- * The present work was carried out in the framework of the research program under the contract no. 180.64.5-ORGI, spon sored by Eur ato m. ** Accepted by W. J. McGonnagle. cation of tubular joints, 44 mm in external diam- eter, 2 mm in thickness, on a standard swaging machine. 2. PROCESS FOR TUBULAR JOINTS Two types of joints have been produced: lap- ped and tapered joints. The fabrication of tap- ered joints between zircaloy-2 and S.S. AISI 304 L is described in this section. In fig. 1 an assembly ready to be swaged is shown. All the S.S. components have been previ- ously degassed in a high vacuum furnace at 1020oc. The surfaces to be welded are chemi- cally pickled prior to assembly: steel by means of an electrolytical bath with phosphoric acid and glycerol; zircaloy by means of a chemical pick- ling with diluted nitric and fluoridric acids. At the end of this operation, aluminum nitrate is then used as a stop solution. Before introducing the assembly into the swaging machine it is heated up to 960oc by an induction coil. The jacket is evacuated and then filled with pure argon. The cold mandrel of bond steel is inserted when the swaging operation starts. The swaging time must be less than 20 sec in order to avoid the cooling effect. Some joints obtained using the described method are shown in fig. 2. The main character- istics of the machine employed are: conical die angle: 20° speed: 1800 pulses per minute power: 10 HP maximum radial force: 40 000 kg.
