Dissolution and isothermal solidification behaviour of commercially pure titanium brazed using a pure nickel filler under TLPB conditions

Abstract

Transient liquid phase bonding of Ti using elemental Ni foils represents a potential low-cost manufacturing route to join aerospace components. To fully develop this technique, the dissolution behaviour and kinetics of isothermal solidification in Ti/Ni joints were determined in this study. During heating, Ti-Ni intermetallic compounds form at the solid/liquid interface, which slows down the dissolution of the Ni foil, while promoting diffusion of Ni into the Ti base metal. These two features limit the amount of liquid gap widening that occurs during initial heating such that it only reaches 55% of the theoretical maximum. Once at the braze temperature of 1050 °C, the rate of isothermal solidification becomes constant with the square root of braze time. The IS rate in the Ti-Ni joints was twice as high as that reported for Ti-Cu joints. Comparison of experimental IS rates with model predictions indicated excellent agreement and demonstrated that the difference in IS rate in Ti-Ni compared to Ti-Cu was largely due to a higher rate of diffusion of Ni in Ti compared to Cu in Ti. The actual time required to achieve isothermal solidification depended both on the amount of dissolution/gap widening and on the rate of IS.