Low-melting-point titanium-base brazing alloys .2. Characteristics of brazing Ti-21Ni-14Cu on Ti-6Al-4V substrate

Filler metal of a low-melting-point (917 degrees C) Ti-21Ni-14Cu was brazed onto the substrate of Ti-6Al-4V alloy at 960 degrees C for 2, 4, and 8 h to investigate the microstructural evolution and electrochemical characteristics of the brazed metal as a function of the period of brazing time, Optical microscopy, scanning and transmission electron microscopy, and x-ray diffractometry were used to characterize the microstructure and phase of the brazed metal; also, the potentiostat was used for corrosion study, Experimental results indicate that diffusion of copper and nickel from the filler metal into the equiaxed alpha plus intergranular beta structure of Ti-6Al-4V substrate causes the lamellar Widmanstatten structure to form, The intermetallic Ti2Ni phase existing in the prior filler metal diminishes, while the Ti2Cu phase can be identified for the metal brazed at 960 degrees C for 2 h, but the latter phase decreases with time, Advantage might be taken from the evidence of faster diffusion of nickel than copper along the beta phase to the substrate, In deaerated Hank's solution, corrosion potential, corrosion current density, and critical potential for active-to-passive transition decrease while the passivation range broadens with the period of brazing time, However, all the brazed metals, immersed for different periods in oxygen-saturated Hank's solution, show similar corrosion behavior, irrespective of the brazing time.