采用非晶态Ti-Zr-Cu-Ni箔带钎料对SP700/TC4钛合金蜂窝结构进行钎焊工艺研究,分析了钎焊温度和保温时间对钎焊接头组织和力学性能的影响.结果表明,当钎焊温度在875～ 890℃之间变化时,随温度升高,钎焊接头中元素扩散更为充分,接头拉脱强度持续增长;在890℃下保温2～4h不同时长进行钎焊,接头的拉脱强度先逐渐增加,在保温时间为3.5h时达到最大值,随后逐渐降低.获得SP700/TC4钛合金蜂窝结构的较优钎焊工艺为890℃/3.5 h,该工艺下钎焊接头的室温拉脱强度、三点弯曲强度、平面压缩强度、L及W方向抗剪强度分别达到14.64,224.05,11.21,4.43及3.76 MPa,破坏部位均为TC4蜂窝芯.

The brazing joint of the Ti-6Al-4V alloy was produced with a designed brazing filler alloy and the optimized brazing temperature which is lower than the β-phase transformation of the matrix. The strength and the ductility of brazing joined Ti-6Al-4V samples were evaluated by conventional tensile tests with a DIC 2D–strain field measurement. The Widmanstätten microstructure with no voids or cracks or intermetallic compounds was found throughout the joint with a width of β-lamellar as ~1μm. Due to the fine acicular α-Widmanstätten and β-lamellar, and the uniformly diffused filler elements throughout the entire joint, the strength of the joint was as much as the matrix. In addition, the hardness test results agreed well with the tensile strength tests. All fractures occurred in the matrix rather than the brazing joints. Furthermore, the maximum local tensile strain was measured as 20% in the matrix, while under the same stress, the brazing joint only reached 6.3% tensile plastic strain. Thus, the mechanical properties of the joint with the associated microstructure demonstrated that a successful brazing filler alloy has been developed for the Ti-6Al-4V alloy.

Microstructure and macro-micro mechanical properties of the joints of Ti-xZr-15Cu-10Ni brazing fillers (mass fraction x=10, 18, 37.5) were studied by in-situ tensile test, SEM, EBSD and EDX. It was found that although the increase in the Zr level lowers the melting point of the brazing materials, which is beneficial to reduce the time of manufacturing and the wear of the equipment, the brazing joints became harder due to solid solution hardening and transformed from a ductile to brittle fracture mode. The microstructural analysis revealed that the increase of Zr level increases the grain size, which leads to high strain gradient across the brazing joints. Thus, high Zr in the brazing joints reduces the ductility of the joints. In this study 10% Zr is found to be the most compatible one with the Ti-6Al-4V matrix. However, in practice, 18Zr is the optimal brazing material for engineering applications due to the balance of the mechanical performance, cost, reliability and applicability.

针对钛合金薄壁结构的钎焊制造技术,通过研究在钎料作用和不同钎焊温度下基体材料的微观组织、相变点、刚度和屈服强度的变化发现,钎料元素扩散导致TC1材料相变点降低,在875℃发生α+β→β相转变,而TC4钛合金直至905℃尚未发生α+β→β相转变.在875℃下,随着保温时间延长,TC4材料的晶粒尺寸有所长大,导致刚度和屈服强度明显下降.当钎焊温度为875℃,保温时间不大于60min时,TC4钛合金板材的刚度和屈服强度不低于原始材料的86％.确定出TC4/TC1钛合金异质钎焊工艺范围为865～875℃、保温30～60min.研究结果为钛合金蜂窝结构的钎焊制造技术提供理论依据和参考.

Brazing joining process offers a better structure integrity performance than traditional welding due to its lower melting point, considerable improved strength and narrower joining lines. It has been useful widely in aerospace industry for joining high-performance titanium alloys into a sandwich honeycomb structure, which enhances the weight reduction of aero vehicles. This research focuses on the effects of Zr content of the filler metal on brazing Ti-6Al-4V alloy sandwich structure as Zr was found to have profound influence on brazing performance e.g. brazing temperature, wettability and strength. Three different Zr content brazing filler materials were studied including two of them were designed. The associated joint tensile strength and microstructure by these three fillers were systematically evaluated. It is of interest to see that lower Zr content results in poorer brazing wettability while high Zr content leads to a reduction in strength due to the formation of interface compounds, which is an undesired phase lowering the toughness of joining. The appropriate Zr content (18 wt%) is identified with an excellent combination of strength (22.3 MPa), wettability and brazing temperature (1173 K). A range of microstructure characterization tools including (SEM, TEM and EDX) were used to reveal the effect of Zr contents on local microstructure and explore the reasons for strength and wettability weakening.