Dissimilar joints between stainless steels and Zr-based alloys, such as Zircaloys and Zr-2.5% Nb, find numerous applications in nuclear reactors.

Joining these materials using conventional fusion welding techniques leads to the formation of hard and brittle intermetallic compounds at the joint interface due to metallurgical incompatibility between them.

To address the challenges associated with fusion welding, an alternate joining technique, based on diffusion bonding, has been developed.

In this study, an effort was made to join these alloys using interlayers of Ni and Ti. Diffusion bonding experiments were performed in the temperature range 825-875 °C under 10-5 mbar vacuum in a vacuum hot press.

The duration of bonding was varied between 60 min and 120 min. A detailed microstructural characterization of the joint interface was carried out using field emission electron probe micro-analyser (FE-EPMA) and transmission electron microscope (TEM).

The maximum shear strength of the joints was found to be 252 MPa. The optimized bonding parameters with respect to the shear strength and microstructure were found to be 850 °C for a bonding duration of 60 minutes.

The microstructure of interfaces in these joints showed them to be devoid of pores, cracks and discontinuities. However, continuous layers of Ni3Ti, NiTi, and NiTiZr intermetallic compounds were found to form in the interdiffusion zone, parallel to the interface. Additionally, the NiZr2 phase appeared as a band of precipitates along the B(Zr, Ti)/Zr-2.5%Nb interface.

This article is shared by V. Srikanth, A. Laik, Vishal Singh, H. Donthula and R. Tewari.