The Application of 40Ti-35Ni-25Nb Filler Foil in Brazing Commercially Pure Titanium

Abstract

The clad ternary 40Ti-35Ni-25Nb (wt %) foil has been applied in brazing commercially pure titanium (CP-Ti). The wavelength dispersive spectroscope (WDS) was utilized for quantitative chemical analyses of various phases/structures, and electron back scattered diffraction (EBSD) was used for crystallographic analyses in the brazed joint. The microstructure of brazed joint relies on the Nb and Ni distributions across the joint. For the β-Ti alloyed with high Nb and low Ni contents, the brazed zone (BZ), consisting of the stabilized β-Ti at room temperature. In contrast, eutectoid decomposition of the β-Ti into Ti2Ni and α-Ti is widely observed in the transition zone (TZ) of the joint. Although average shear strengths of joints brazed at different temperatures are approximately the same level, their standard deviations decreased with increasing the brazing temperature. The presence of inherent brittle Ti2Ni intermetallics results in higher standard deviation in shear test. Because the Ni content is lowered in TZ at a higher brazing temperature, the amount of eutectoid is decreased in TZ. The fracture location is changed from TZ into BZ mixed with α and β-Ti.