Infrared brazing of Ti50Ni50 shape memory alloy and 316L stainless steel with Au-22Ni-8Pd filler

Abstract

The microstructural evolution and shear strength of Ti 50 Ni 50 SMA and 316L SS infrared brazed with a gold-based filler metal Au-22Ni-8Pd (BAu-6) at 1050°C for 180 and 300 s were investigated. The results of dynamic wetting angle measurement indicate that Au-22Ni-8Pd filler metal exhibits rather good wettability on Ti 50 Ni 50 and 316L SS substrates if the specimens are brazed at 1050°C for longer than 100 s. Experimental results of SEM BEIs and EDS/WDS show that the joint brazed for 300 s is composed of a layer of Ni 3 Ti+ TiNiAu lamellae, a layer of TiNiAu and Ti(Au,Ni) 4 intermetallics, and a layer of TiNi 2 Au one at Ti 50 Ni 50 substrate side, and is a layer of the mixture of (Ni, Fe)+(Au) solid solutions and a layer of (Ni, Fe) solid solution with no interfacial reaction compound formed at 316L SS substrate side. All the formed lamellae/layers increase in thicknesses as the brazing time is prolonged, which prevents the brittle Ni 3 Ti lamellae from contacting the layer of TiNi 2 Au. Accordingly, the joint shear strength improves as the brazing time increases. The shear strength of a joint brazed for 300 s can reach 204 MPa, where the fracture crack begins around the interface of the TiNi 2 Au and layer TiNiAu/Ti(Ni,Au) 4 layers. Cleavage-dominated fracture is observed in SEI fractographs.

Interfacial Reaction and Bonding Strength of Ti₅₀Ni₅₀ and Inconel 600 Dissimilar Brazed Joints

“…At the same time, the thickness of layer D, in which a few small Bb 2 particles are embedded, increases with the longer brazing time. Area E shows a lamellar mixture of (Ni,Au) solid solution and Ti(Ni,Au) 3 phase, which has also been observed in Ti 50 Ni 50 / Au-22Ni-8Pd/316L SS joints infrared brazed at 1,050 C for 180 s and 300 s. 8) The microstructural evolution and related reaction mechanisms on both substrate sides can be elucidated as follows. On the Ti 50 Ni 50 substrate side, to identify the formed intermetallics observed in Fig.…”

“…10) Comparing the curve of the dynamic wetting angle vs. the infrared brazing time of Au-22Ni-8Pd/Inconel 600 to that of Au-22Ni-8Pd/316L SS, the wetting of Au-22Ni-8Pd/Inconel 600 is much better than that of Au-22Ni-8Pd/316L SS. 8) The dissolution of 316L SS substrate into the Au-based braze melt is inferior to that of Inconel 600 due to limited solubility of Fe in Au-based braze. , and a layer of Ti-Ni-Au (II) intermetallic compound that is a discontinuous layer (marked Da) or a continuous layer (marked Db) next to the ller metal, as illustrated in Fig.…”

“…However, the phase diagram for Ti-Ni-Cu shows that TiNiCu and TiNi 2 Cu intermetallics form in this ternary alloy system. 8,19) Comparing the Ni-Cu binary phase diagram with the Ni-Au one, one can nd that both diagrams indicate complete solid solubility at high temperature. 9) In addition, the Ti-Cu and Ti-Au binary phase diagrams show that in the range of Ti ≦ 50 at%, TiCu, TiCu 2 , and TiCu 4 intermetallics will form in the former, and TiAu, TiAu 2 , and TiAu 4 will form in the latter.…”

“…6,7) However, dissimilar brazing Ti 50 Ni 50 SMA is seldom studied in literature. 8) Gold-based ller metals have been used to braze iron-, nickel-and cobalt-based alloys where oxidation and/ or corrosion resistance is required. In our previous study, 8) Ti 50 Ni 50 SMA was infrared brazed with 316L stainless steel (SS) using Au-22Ni-8Pd (in mass%, AWS classi cation: BAu-6) ller metal, and the joint infrared brazed at 1,050 C for 300 s achieved a shear strength of 204 MPa.…”

“…8) Gold-based ller metals have been used to braze iron-, nickel-and cobalt-based alloys where oxidation and/ or corrosion resistance is required. In our previous study, 8) Ti 50 Ni 50 SMA was infrared brazed with 316L stainless steel (SS) using Au-22Ni-8Pd (in mass%, AWS classi cation: BAu-6) ller metal, and the joint infrared brazed at 1,050 C for 300 s achieved a shear strength of 204 MPa. Infrared brazing of Ti 50 Ni 50 SMA and Inconel 600 alloy with Cusil-ABA (Ag-35.25Cu-1.75Ti in mass%) and Ticusil (Ag-26.7Cu-4.5Ti in mass%) ller metals has also been investigated.…”