A novel Zr-Ti-Ni-Cu eutectic system with low melting temperature for the brazing of titanium alloys near 800 °C

This article reports on low (below 800 °C) melting temperature characteristics of a Zr-Ti-Ni-Cu alloy system, designed by adding a small amount of Cu to a Zr-Ti-Ni eutectic alloy system in the Zr-rich corner of the Zr-Ti-Ni system. A series of Zr-Ti-Ni-Cu-based alloy buttons of varying Cu content was fabricated by an arc melting machine. The melting temperature ranges of the quaternary alloys were systematically examined by differential thermal analysis (DTA). As a result, a quaternary eutectic alloy of composition Zr₅₄Ti₂₂Ni₁₆Cu₈ with a low melting temperature range from 774 °C to 783 °C was found. In addition, structural and chemical analysis results for the slowly solidified, quaternary eutectic alloy sample revealed equivalent quaternary eutectic structure and phases to those of the ternary eutectic Zr₅₀Ti₂₆Ni₂₄ alloy, except for a small amount of Cu dissolved in individual constituent phases. The wetting angle tested at 800 °C for 60 s on the commercially pure titanium was about 25°.