Abstract
Brazing of titanium provides a joining technique suitable for the fabrication of highly-loaded aerospace components, but it still poses numerous challenges, such as the formation of brittle intermetallic interphases. This study of the interphase formation in brazed joints consisting of different titanium alloys (Ti-CP2, Ti-CP4, Ti-6Al-4V, Ti-6Al-2Mo-4Zr-2Sn) and Ag28Cu shows that complex reactions lead to the formation of various intermetallic phases including a Ti2Cu-TiCu boundary zone. The compositions of the titanium alloys influenced the particular microstructures, which have been characterized with various methods including synchrotron X-ray microtomography. Tensile tests evidence high ultimate tensile strengths that are, importantly, not directly limited by the strength of the brazing alloy. The strength of the Ti2Cu-TiCu phase boundary is significantly increased by the alloying elements in Ti-6Al-4V and Ti-6Al-2Mo-4Zr-2Sn and the crack paths change from boundary failure to transcrystalline fracture through TiCu as well as Ag-rich regions. Cu diffusion into the titanium substrate, leading to a coarse grained β-phase that transforms eutectoidally into a lamellar α-Ti + Ti2Cu structure during cooling, occurred in all systems except Ti-6Al-2Mo-4Zr-2Sn where Mo stabilized a fine grained microstructure and enabled the formation of a columnar TiCu structure.
Highlights
Brazing is currently being investigated as a joining technique for manufacturing aerospace components made of Ti alloys [1,2]
In a previous study [11] we found that the composition of the titanium matrix significantly affected the formation of the intermetallic structure in the transition zone, which in consequence resulted in different fracture modes
The chemically unaffected base Tifor alloy, a transition zone interpretation of the material systems: The chemically unaffected base Ti alloy, a transition zone consisting of chemically modified base alloy as well as intermetallic phases, and the Ag-rich region
Summary
Brazing is currently being investigated as a joining technique for manufacturing aerospace components made of Ti alloys [1,2]. This technique is used for joining similar or, importantly, dissimilar [3,4] metallic parts by melting a brazing solder with a melting point lower than that of the base materials. Ag-Cu-based alloys [5,6] The latter are attractive owing to their low melting point, suitable wetting behavior and relatively high strength [5]. Diffusion of Cu from the solder into the base material. Depletion of Cu in the melt, especially in the vicinity of the base material
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