Glass to metal seals are widely employed in lighting and electronic devices, automotive, and medical fields [
1]. The glass to metal seal is traditional a fusion technique with the glass melted in contact with metal parts to be sealed to. Matched thermal expansion seals, unmatched expansion seals, soldered seals, and mechanical joints are the four major sealing methods of glass to metal [
2]. Recently, high-frequency induction heating is used to seal the glass to the Kovar in solar receiver tubes and developed a highly automated process [
3]. Due to the nonlinear absorption characteristics of ultrashort-pulsed lasers, ultrashort lasers have attracted significant attention for their application in the fields of cutting [
4] and surface mechanical characterization [
5]. Laser welding is considered to be a highly-flexible technique with potential for joining glasses and metals. Carter et al. reported systematic analysis and comparison of picosecond laser microwelding of industry relevant Al6082 parts to SiO
2 and BK7 [
6]. Volpe et al. reported on femtosecond laser microwelding of two transparent layers of polymethyl methacrylate (PMMA) based on nonlinear absorption and localized heat accumulation at high repetition rates [
7]. For laser transmission welding of glass and metals [
8], the laser transmission welding of copper substrates with borosilicate glass was achieved using a femtosecond laser by Itoh et al. Although the melting point and thermal-expansion coefficient of these two materials are quite different, a relatively reliable connection was formed between the two materials [
9]. Utsumi reported a direct welding of copper balls with borosilicate glass using a short-pulsed laser [
10]. Quintino et al. used a femtosecond laser with a pulse width of 35 fs for laser transmission welding of glass flakes with NiTi alloy flakes. It has been shown that the NiTi particles were formed and splashed in a direction perpendicular to the laser propagation after the laser pulses impacted on the surface. A dimple structure was observed at the weld, indicating a good connection between the two materials [
11]. Flury successfully prepared metal lattices on a glass substrate using a glass surface coating to induce reverse transfer by a femtosecond laser [
12]. Ciuca et al. used a picosecond laser to achieve transmission welding between quartz glass and aluminum, and found that the nanocrystalline silicon,
γ-Al
2O
3, and
δ-Al
2O
3 were formed in the weld zone [
13]. Carter et al. used a picosecond laser to weld a variety of metals such as aluminum, copper, and stainless steel with glass, and found that cracks existed at the interface between metal and glass [
14].
The high price of ultrashort-pulsed lasers makes them impractical for application in laser transmission welding technology for welding between metal and glass. Lin et al. used a relatively inexpensive long-pulsed fiber laser to achieve the welding of quartz and anodized aluminum [
15]. Wetting is very important to enhance the thermo-mechanical properties in the manufacture of metal matrix composite materials, and reactive infiltration. Narciso et al. enhanced interfacial thermal conductivity in Al/Diamond composites by diamond surface modification [
16], and studied the porosity effect on thermal properties of Al-12 wt % Si/Graphite composties [
17]. In addition, to improve the strength and hermeticity of the joints, the pre-oxidation was used to form an oxide film on the metal surface. Chern et al. improved the wettability and tightness of 7056 glass on a Kovar surface by pre-oxidizing the surface of Kovar alloy using a furnace thermal treatment [
18]. Zhang et al. improved the wettability and diffusivity of borosilicate glass on the surface of Kovar alloy by laser melting oxidation of metal surfaces [
19]. Li et al. improved the joint strength of PS and titanium using the two pretreatment methods (laser oxidization treatment and oxygen plasma surface treatment) [
20]. Moreover, the laser surface treatment does not require pre-oxidation, and heat preservation of the entire part and the local oxidation of the metal surface can be quickly achieved with good selectivity and repeatability.
The welding of titanium alloy with high borosilicate glass was investigated in this study; it was found that the welding strength of high borosilicate glass with titanium alloy without surface oxidation was very low. To improve the joint strength, the surface of the titanium alloy was first locally oxidized using a semiconductor laser, and transmission welding of titanium alloy with borosilicate glass was then conducted using a long-pulsed Nd:YAG laser. The influence of laser surface treatment on the welding strength of laser transmission welding and the welding mechanism of titanium alloy with high borosilicate glass were studied by analyzing the microstructure, the tensile-fracture failure mode of the weld, the interface elemental diffusion, and the surface free energy.