Microstructural features of hot pressure bonding between stainless steel type AISI-304 L and Zircaloy-2

Abstract The diffusion zone formed after reaching quasi-equilibrium in hot pressure bonding between stainless steel type AISI-304 L and Zircaloy-2 under particular thermal and compressive conditions (1000–1100°C and 2–3 atm) contains two distinct layers, each separately localized in the modified stainless steel and Zircaloy matrices. SEM, TEM, X-ray diffraction and microanalysis were used to identify the phase structure and composition of the two diffusion layers. The nature and distribution of phases found in the diffusion layers can be explained in connection with the diffusion mechanisms operating after the initial stages of bond formation and interface disappearance: (a) The strong zirconium diffusion promotes ferrite and ZrCr 2 formation in a narrow zone located near the stainless steel matrix, (b) Iron and nickel diffusion over large distances in the Zircaloy matrix leads to the occurrence of a larger zone having a two-phase structure. The light grey phase consists of untransformed α-Zr and a small percentage of high-temperature β-Zr phase. The darker grey phase contains essentially a very high amount of intermetallic bct compounds Zr-Fe-Ni, Zr 2 Fe and Zr 2 Ni dispersed in the small residue of Zircaloy matrix.