Infrared Dissimilar Joining of Ti50Ni50 and 316L Stainless Steel with Copper Barrier Layer in between Two Silver-Based Fillers

Abstract

Infrared dissimilar joining Ti50Ni50 and 316L stainless steel using Cu foil in between Cusil-ABA and BAg-8 filler metals has been studied. The Cu foil serves as a barrier layer with thicknesses of 70 μm and 50 μm, and it successfully isolates the interfacial reaction between Ti and Fe at the 316L SS (stainless steel) substrate side. In contrast, the Cu foil with 25 μm in thickness is completely dissolved into the braze melt during brazing and fails to be a barrier layer. A layer of (CuxNi1−x)2Ti intermetallic is formed at the Ti50Ni50 substrate side, and the Cu interlayer is dissolved into the Cusil-ABA melt to from a few proeutectic Cu particles for all specimens. For the 316L SS substrate side, no interfacial layer is observed and (Ag, Cu) eutectic dominates the brazed joint for 70 μm/50 μm Cu foil. The average shear strength of the bond with Cu barrier layer is greatly increased compared with that without Cu. The brazed joints with a 50 μm Cu layer demonstrate the highest average shear strengths of 354 MPa and 349 MPa for samples joined at 820 °C and 850 °C, respectively. Cracks are initiated/propagated in (Ag, Cu) eutectic next to the 316L substrate side featured with ductile dimple fracture. It shows great potential for industrial application.

Keywords

• shape memory alloy
• stainless steel
• barrier layer
• infrared brazing
• microstructure