Abstract
Dissimilar metal joining between titanium and kovar alloys was conducted using electron beam welding. Metallurgical bonding of titanium alloys and kovar alloys was achieved by using a Cu/Nb multi-interlayer. The effects of welding speed on weld appearance, microstructure and mechanical properties of welded joints were investigated. The microstructure of welded joints was characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectroscopy (EDS). The mechanical properties of welded joints were investigated by tensile strength and micro-hardness tests. The results showed that welding speed had great effects on the weld appearance, microstructure, and mechanical properties of electron beam-welded joints. With an increase of welding speed, at the titanium alloy side, the amount of (Nb,Ti) solid solution was increased, while the formation of brittle FeTi was effectively suppressed. At the kovar alloy side, microstructure was mainly composed of soft Cu solid solution and some α-Fe + γ phases. In addition, higher welding speeds within a certain range was beneficial for eliminating the formation of cracks, and inhibiting the embrittlement of welded joints. Therefore, the tensile strength of welded joints was increased to about 120 MPa for a welding speed of 10 mm/s. Furthermore, the bonding mechanism of TC4/Nb/Cu/4J29 dissimilar welded joints had been investigated and detailed.
Highlights
Kovar alloy is widely applied in the field of electronic industry, which has a coefficient of thermal expansion that is similar to hard glass [1]
The results showed that the Cu–Ti intermetallic compounds (IMCs) with a lower hardness than that of Fe–Ti IMCs formed in the fusion zone
Our study demonstrated that the regulating of welding speed was effective for inhibiting the formation of brittle Fe–Ti IMCs and improving the quality of welded joints
Summary
Kovar alloy is widely applied in the field of electronic industry, which has a coefficient of thermal expansion that is similar to hard (borosilicate) glass [1]. A FeTi intermetallic compound was produced in the fusion zone during micro-resistance spot welding of a titanium alloy and a 316L stainless steel [7] It appears that the challenge in bonding kovar alloys and titanium alloys is the production of the brittle Fe2 Ti and FeTi. For the sake of inhibiting the formation of substantial brittle IMCs, it is beneficial to control the mixing of chemical components by inserting a metallic interlayer. If titanium alloy and stainless steel were welded by electron beam welding with a V/Cu multi-interlayer, the formation of brittle Fe–Ti IMCs was effectively inhibited so as to enhance the quality of welded joints [15]. Our study demonstrated that the regulating of welding speed was effective for inhibiting the formation of brittle Fe–Ti IMCs and improving the quality of welded joints
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