Phase Transformation of a Ti-15Mo-5Zr-3Al Brazed Joint Using Clad Ti-15Cu-15Ni Filler

Abstract

Furnace brazing of Ti-15Mo-5Zr-3Al (Ti-15-5-3, β-Ti) alloy using clad Ti-15Cu-15Ni foil as the filler in a high vacuum has been carried out. In the brazed joints, the chemical compositions of distinct phases were quantified by electron probe micro-analyzer (EPMA), and the phase structures were identified by electron backscatter diffraction (EBSD). The as-brazed joint composed of α-Ti, retained β-Ti, Ti2Ni, and Ti2Cu. The embrittlement of the brazed joint was correlated mainly with the formation of intermetallics, especially cellular Ti2Ni dendrites in the brazed zone. It was noticed that the molten filler liquated the β-Ti grain boundaries and assisted the eutectic reaction therein, resulting in forming grain boundary Ti2Ni surrounded by the retained β-Ti. The results indicated that proper brazing conditions were able to eliminate all the harmful phases effectively, and increased the shear strength of the Ti-15Mo-5Zr-3Al brazed joint.