The Study of Infrared brazing Ti50Ni50 SMA and Incoloy 800/Inconel 600 Alloys

BAg-8, Cusil-ABA, Copper, and Au-22Ni-8Pd fillers are used to infrared braze Ti50Ni50 and three other alloys, Incoloy(IY) 800, Inconel(IN) 600 and 316L stainless steel(SS). The brazed joint’s interfacial reaction, microstructure evolution and shear strength are investigated. Cu film is used as a diffusion barrier in the three-layer filler to become a TiNi/Cusil-ABA/Cu/BAg-8/IY 800 joint to prevent the formation of brittle intermetallics in the joint, which composes of (CuxNi1-x)2Ti, Cu-rich, Cu, and Ag-Cu eutectic. When Cu film thickness is 50μm, the shear strength is 271MPa for the joint brazed at 850℃×3min, but when its thickness increases to 70μm, the joint’s shear strength reaches 181 MPa due to its thickness is over. However, when its thickness is reduced to 25μm, it cannot prevent the formation of brittle Ti-Fe intermetallics and the shear strength reduces to 222 MPa. For joining TiNi and IN 600 using AuPdNi filler, a lamellar sturctuer of TiNi3 and Ti-Ni-Au(I), and a layer of Ti-Ni-Au(II) can be observed at TiNi side, and solid solution of AuPdNi and that of (Au,Ni) can be observed at IN600 side. The shear strength can reach 527 MPa when it is brazed at 1050℃×5min. For TiNi/Cusil-ABA/50μm Cu/BAg-8/IN 600 joint, it is also composed of (CuxNi1-x)2Ti, Cu-rich, Cu, and Ag-Cu eutectic, and has the shear strength of 374MPa for brazing at 820℃×5min. For TiNi/Cusil-ABA/Cu/BAg-8/316L SS joint, it is composed of (CuxNi1-x)2Ti, Cu-rich, Cu, and Ag-Cu eutectic and is similar to those of barzing TiNi/Cusil-ABA/Cu/BAg-8/IY 800 joint with a Cu diffusion barrier. The shear strength of this joint using 50μm Cu film is 354MPa brazed at 820℃×5min. When the thickness of Cu film reduced to 25μm, Ti-Fe brittle intermetallics appear at 316L SS side, and the shear strength is reduced to 140 MPa at 820℃×5min.