| Popis: |
The microstructural evolution and shear strength of Ti50Ni50 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 Ti50Ni50 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 Ni3Ti + TiNiAu lamellae, a layer of TiNiAu and Ti(Au,Ni)4 intermetallics, and a layer of TiNi2Au one at Ti50Ni50 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 Ni3Ti lamellae from contacting the layer of TiNi2Au. 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 TiNi2Au and layer TiNiAu/Ti(Ni,Au)4 layers. Cleavage-dominated fracture is observed in SEI fractographs. |
