| Zirconia exhibits high wear resistant and high hardness. However, most of advanced ceramics, including zirconia is difficult to fabricate into large and/or complex shaped components. Joining ceramics to metals can make full use of the features of ceramic, and the advantages of metals such as the toughness. Amorphous alloy, a material at unsteady state, can accelerate atomic diffusion and surface reaction during brazing process, which are superior to the corresponding crystalline alloy.The wetting behavior of Ti47Zr28Cu14Ni11 BMG on zirconia substrate was investigated by a modified sessile drop method under high vacuum. The adsorption and accumulation of the active atoms such as Ti and Zr at the interface and the interfacial reaction played a key role in determining the wettability. Oxygen from ZrO2 led to the oxidation of active elements at the precursor of the triple line, which prevented the triple line from moving. As a result, the contact angle was high. The oxidation behavior in the wetting system was different from that in the brazing system. In the brazing process, the oxidation of active elements at interface led to a good joint.The influence of some critical experimental parameters on the characteristics of the joints was discussed with particular emphasis on the microstructural features and shear strength. Based on the systematic study of the microstructure, the bonding mechanism and interfacial reaction were studied. The shear strength was tested to evaluate the mechanical property of the joint and the relationship between microstructures and mechanical property were investigated.The results showed that titanium reacted with zirconia to form titanium oxides TiO and Cu(Ni)2Ti4O at the joint interface. The TiO+ Cu(Ni)2Ti4O reaction layer thickness was important to the strength of a joint. When the center of brazing seam was a fine eutectic structureα-Ti+(Ti,Zr)2(Cu,Ni),and the eutectic structure distributes on the white phase(Ti,Zr)2(Cu,Ni), the shear strength was improved. When the brittleα-Ti martensite plate appeared, the joints had a low strength. With increasing brazing temperature and holding time, (Ti,Zr)2(Cu,Ni) decreased andα-Ti martensite increased in the content. The thicknesses of the TiO+ Cu(Ni)2Ti4O reaction layer decreased, while the brittleα-Ti martensite plate increased, which resulted in a lower strength. When the holding time was longer than 45min, the eutectic structure disappeared, while the brittleα-Ti martensite plate appeared, which decreased the shear strength of joint. With increasing the thickness of brazing filler, the thickness of (Ti,Zr)2(Cu,Ni) reaction layer increased, which was unfavorable to the joint. The cooling rate played little role on the microstructure, but increasing the cooling rate increased the residual stress of the joint region. So, the appropriate parameters, such as brazing temperature 850 oC, holding time 45min, thickness of brazing filler 35μm and cooling rate less than 10 oC/min were used. Accordingly, the maximum shear strength is 77.9 MPa.Above all, the brazing temperature played a most important role on the interfacial structure. The fractured occurred in the brazing seam. Fracture location was studied. The influence of the phases on the shear strength was analyzed. Formation of brittle reaction products at the interface was unfavorable to the joint. |
PDF Full Text Request