| Titanium tube could be used in satellite attitude control device which demands excellent corrosion resistance ability and high-temperature strength, while its quality and precision are also strictly required. TA15titanium alloy has good thermal stability, welding performance, and the longtime working temperature up to500℃, which makes it could be used as a kind of great potential material in this area. Therefore, there’s an inevitably challenge for material connection. However, The conventional welding method always bring deformation and defects to the joints, thereby affecting the precision and reliability. Hence, vacuum brazing with amorphous filler metal becomes a feasible and effective way to overcome the disadvantageous of common crystal Ti-based filler metal. According to these issues, Three kinds of the filler metal are designed based on the fundamental principle of brazing. TA15alloy has been brazed at different parameters using these Ti-based amorphous filler metal.Ti-based filler metals designed in this airtical include three kinds:FM3(Filler Metal3, TiZr22Cu20Ni15), FM8(TiZr28Cul5Ni15),and FM15(TiZr35Cul0Ni9Co6). The range of liquid’s temperature is830-855℃, which is far lower than the beta phase transition temperature of TA15titanium alloy. What’s more, they all have good wetting and amorphous formation ability. Solder alloys have been made into foils through single roller quick-cooling equipment with thickness in60～80μm interval. It is very suitable for assembly.Both FM3and FM8belong to the Ti-Zr-Cu-Ni system. Along with the elevation of brazing temperature of Ti-Zr-Cu-Ni filler metal, a phase begin precipitated from β phase. In addition, three crystal forms of a phase are evolved during the growth: acicular a phase, lath-shaped a phase and layer flake a phase. And it causes the content of β phase to decrease. With the increase of brazing temperature, the activity stable elements of β phase have diffused into base metal, which makes that base metal are dissolved by filler metal. And the width of weld seam increases. Micro-hardness of weld zone increases with the elevation of brazing temperature, and reduces rapidly when the temperature come to970℃. Micro-hardness reaches the maximum at950℃.The joints brazed with FM3and FM8at950℃for40min exhibites the highest room temperature strength372±16.6MPa and329±13.8MPa.But elements distribute more even in the brazing interface brazed with FM3. Besides, the mechanical stability and the toughness of joints are also excellent. These elements promote the diffusion between filler metal and TA15alloy, which makes FM15exhibite optimal wetting ability in the three Ti-based filler metal. Moreover, the addition of Co decrease the local enrichment of the activity stable elements of β phase(Cu and Ni).The dissolution of base metal by filler metal is also restrained. Under the same experimental condition, the tensile strength of the joints brazed with FM15are higher than joints brazed with Ti-Zr-Cu-Ni filler metal in the mass. For FM15filler metal, it is found that an intensive alloying reaction occurres between the molten filler metal and the base metal even at lower brazing temperature. Yet, the size of a phase eparates in the weld seam with FM15is stubbier. Along with the elevation of brazing temperature reached950℃with FM15, the diffusion between filler metal and base metal is enhanced. Furthermore, the strengthening function of the stable elements of a phase and β phase reaches the maximization, and it makes the micro-hardness arrive at the maximization at950℃too. The tensile strength of joints brazed with FM15is403±18.5MPa at950℃for30min.The result showes that the fracture mode of all joints represented brittle fracture characteristics. |
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