Interfacial interactions between 304L stainless steel and Zy-4 alloy during isothermal holdings at 1050 °C

The transition from solid-state bonding of the stainless steel 304L (SS) with Zircaloy-4 (Zy-4) to a partial liquid phase bonding is very important for the bonding process at 950-1050 degrees C. Previous studies demonstrate that the growth rate of the reaction product zone (RPZ) at 1050 degrees C show an intermediate behaviour which is interesting from an industrial point of view regarding the partial phase bonding process. In this work, the interfacial interactions between SS and Zy-4 during isothermal holdings at 1050 degrees C are studied for holding times up to 45 min. Diffusion couples were characterized by ESEM-EDS-EBSD and EPMA techniques. The RPZ consists of three layers: the first layer LI consists of alpha-(Fe,Cr) phase and its thickness increases very slightly with the holding time. On the contrary, the thickness, the morphology and the nature of the phases formed in the LII and LIII layers strongly depend on the interaction time. Based on the experimental results of this study, a schematic evolution of SS/Zy-4 system and mechanisms of interfacial interactions during isothermal holdings at 1050 degrees C are proposed. This study leads to a better understanding of the complex phenomena intervening in the SS/Zy-4 joining process which is very useful for applications in industrial scale. (C) 2019 Elsevier B.V. All rights reserved.