Interfacial reactions and strength properties of diffusion bonded joints of Ti64 alloy and 17-4PH stainless steel using nickel alloy interlayer

Abstract

Interfacial reactions and strength properties of diffusion bonded joints between Ti64 alloy (Ti64) and 17-4 precipitation hardening stainless steel (PHSS) using a nickel alloy (NiA) as an interlayer was carried out in the temperature range of 800–900°C in steps of 25°C for 45min and at 900°C for 5, 10, 15, 30 and 45min in vacuum. The effects of bonding temperature and time on interface reactions of the bonded joint were characterized by scanning electron microscopy and electron probe microanalyser. The interfaces indicate that Ni–Ti base reaction products are formed at the NiA–Ti64 interface and the PHSS–NiA interface is free from intermetallics up to 875°C for 45min processing temperature and at 900°C up to 15min processing time. The bright regions of Fe5Cr35Ni40Ti15 have been observed within the Ni3Ti intermetallic layer. Fe–Ti and Fe–Cr–Ti bases reaction products have been observed beyond 15min processing time at 900°C temperature. Joint tensile was measured; a high tensile strength of ∼517.6MPa along with ∼6.1% elongation was obtained for bonded joint when processed at 875°C for 45min. The bonded samples were fractured through the NiTi2 intermetallic compounds at NiA–Ti64 interface up to 875°C for 45min and up to 15min at 900°C. However, higher processing temperature, the fracture of the joints took place through the phase mixture of NiTi2+Fe2Ti and β-Ti.