Microstructures and hot cracking formed at the interface of Zircaloy-4/stainless-steel-304L junctions

Dissimilar junctions between the zirconium alloy (Zy-4) and 304L stainless steel (SS) are prepared via two bonding processes: solid-phase diffusion at T-1 = 1223 K and in transient liquid phase (TLP) at T-2 = 1293 K and T-3 = 1323 K for an identical isothermal hold time of 2700 s. The formed layers and phases at the interface were characterised by the combination of EDS-EBSD-ESEM, EPMA and X-RD and impact fracturing tests. The Zy-4/SS interface is formed of three layers containing Cr-rich alpha-Fe and Zr(Fe,Cr)(2) and Zr-2(Fe,Ni) intermetallic compounds. We establish the relationship between the interface microstructures and hot cracking formation which are of thermo-mechanical and solidification origin. The knowledge of the solidification path of the TLP obtained in LIII layer at T-2 and T-3 makes it possible to explain the formation of micro-pores. The fracture is for both bonding processes, takes place in the brittle mode, of the intergranular type by cleavage and is in the LIII layer of the junction.