In¯uence of brazing conditions on the strength of brazed joints of alumina dispersion-strengthened copper to 316 stainless steel H. Nishi * , K. Kikuchi Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-11, Japan Abstract Brazing of alumina dispersion-strengthened copper (DS Cu) to 316 stainless steel were conducted in order to in- vestigate the in¯uence of ®ller metals and brazing conditions on the joint strength. The brazing were performed with a silver-base (BAg-8) and three kinds of gold-base (BAu-2,4,11) ®ller metals with varying brazing joint clearance and brazing time. The ®ller metal had a greater eect on the joint strength than the brazing joint clearance and brazing time. The joint with BAu-2 was superior to the joint with other ®ller metals. The tensile strength of the joint with BAu-2 was as large as that of DS Cu, however, the Charpy and low cycle fatigue strength were lower than those of DS Cu. The DS Cu melted near the brazed zone, consequently recrystallization and agglomeration of alumina occurred in the diusion layer for all ®ller metals. The grain size after the recrystallization was small in order of BAu-2, BAu-4 and BAu-11, that was in accordance with the order of the brazing temperature. The excellent fracture strength for the joint with BAu-2 was attributed to the smallest grain size. Ó 1998 Elsevier Science B.V. All rights reserved. 1. Introduction The ®rst wall and divertor components of the ITER are proposed to be made of alumina dispersion- strengthened copper (DS Cu) bonded to austenitic stainless steel, since the DS Cu has excellent thermal conductivity, strength retention and microstructural stability at elevated temperatures. Hence the develop- ment of a bonding technology for the DS Cu has been investigated by brazing [1±5], friction welding [6,7] and diusion bonding [8±11]. As for cooling pipes of the divertor, which are made of the DS Cu and joined to the stainless steel pipes and heat sink materials, the joining technique should not employ high pressure such as used in HIP, because the pipes have poor endurance against compression at elevated temperatures. Therefore, braz- ing will be required in the divertor component. Brazing of the DS Cu to itself has been carried out using mainly silver-base ®ller metal [1±5]. However, all joints were embrittled and exhibited little ductility and low strength compared with the DS Cu base metal. Samal has suggested that gold-base ®ller metals (Au50± Cu50, Au35±Cu65) in the brazing improved the strength and properties of the joint [2]. Only limited data, how- ever, were available on the strength of the brazed joint between the DS Cu and stainless steel using the gold- base ®ller metals. In this work, the brazing of the DS Cu to the 316 stainless steel was conducted in order to investigate the in¯uence of ®ller metals and brazing conditions on the joint strength. The brazing was performed with the sil- ver-base (BAg-8) and the gold-base (BAu-2, BAu-4, BAu-11) ®ller metals varying brazing time and brazing joint clearance, by which tolerance between brazing surfaces of the actual components is aected. According to the results of FEM analyses on the tensile test, the maximum stress and strain were generated apart from the interface in large deformation [12]. The fracture strength on the tensile test does not always correspond to the bonding strength near the interface. Therefore, joint strength was characterized by tensile, Charpy im- pact and low cycle fatigue tests on the joints and base metals in this investigation. Moreover microstructural observations, elements analysis and a hardness of the brazed zone were examined with an optical microscope, SEM, EPMA and a Vickers hardness tester respectively. Journal of Nuclear Materials 258±263 (1998) 281±288 * Corresponding author. Tel.: +81-29-282-6385; fax: +81-29- 282-6489; e-mail: nishi@popsvr.tokai.jaeri.go.jp. 0022-3115/98/$19.00 Ó 1998 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 3 1 1 5 ( 9 8 ) 0 0 2 3 0 - X