Structure and properties correlation of diffusion bonded joint of duplex stainless steel and Ti–6Al–4V with and without Ni–17Cr–9Fe alloy interlayer

Abstract

In this work, the diffusion bonding of duplex stainless steel (DSS) and Ti–6Al–4V (Ti64) with and without nickel alloy (NiA) as an interlayer was investigated in the temperature range of 800–950 °C for 30 min in vacuum. Layer wise σ phase and FeTi + λ phase mixture were observed at the DSS | Ti64 bond interface when joints were made at 875 °C and above temperatures; however, when interlayer was used to facilitate the bonding of both DSS and Ti64, layer wise Ni–Ti-based intermetallic was observed at the NiA–Ti64 interface and the bright irregular-shaped Fe5Cr35Ni40Ti15 phase was observed within the Ni3Ti layer, while the DSS–NiA interface was free from any intermetallic. Direct bonded joints (DSS | Ti64) processed at 925 °C achieved the highest tensile strength (∼498.3 MPa) along with substantial ductility, the highest shear strength (∼385.2 MPa), and the highest impact toughness (∼18 J). Usage of interlayer to process the DSS | NiA | Ti64 joints proved to be advantageous than the DSS | Ti64 joints from the point of view of tensile properties, shear strength, and impact toughness of the bonded joints. DSS | Ti64 joints fail either through FeTi + λ phase mixture or σ phase, depending upon the bonding temperature selected, whereas DSS | NiA | Ti64 joints fracture apparently through NiTi2 layer at NiA–Ti64 interface.