Growth mechanism of compound at interface of Ti-6Al-4V joint brazed with 72Ag-28Cu filler alloy

The growth process of Ti-Cu compound at the interface of a Ti-6Al-4V/72Ag-28Cu (wt-%) joint was analysed using X-ray diffraction, SEM, and energy diffraction spectra. According to the investigated results, when the joint was brazed for a relatively short holding time, atoms of Ti and Cu diffused into the interface would combine into Ti₂Cu by eutectoid reaction during the cooling stage. As the holding time is beyond the critical brazing time, Ti₂Cu compound decomposed owing to a large amount of Ti in the base metal dissolving into the brazing zone and the relatively gentle concentration gradient of Cu, thus resulted in the solid dissolving of Cu into Ti. In this case, the resulting joints exhibited high strengths. On the basis of the analysis mentioned above, a concept ‘critical brazing time’ was proposed.