N. P. Wikstrom, O. A. Idowu, O. A. Ojo, M. C. Chaturvedi, University of Manitoba, Winnipeg, MB, Canada
Transient liquid phase (TLP) bonding has become a very attractive joining and repair technique for difficult to weld aerospace superalloys. The main advantage of this technique is that the formation of brittle centerline eutectic-type microconstituent, which is often damaging to brazed joint properties, can be effectively prevented. This is generally achieved by isothermally holding brazing assembly at brazing temperature for a time period that is sufficient to attain complete solidification of the liquated filler through the diffusion of melting point depressant element away from the liquid. The time required for a complete isothermal solidification is usually reduced through a higher solidification rate by increasing brazing temperature. However, in the present work, in Inconel 738LC and Waspaloy TLP bonded with Nicrobraz 150 and DF3 commercial filler alloys, a critical temperature (Tc) was observed to exist, for a given joint width, above which isothermal solidification rate started to decrease. This resulted in the formation of a different type of eutectic microconstituents, which could be deleterious to the properties of the joint. The existence of Tc, is contrary to the current conventional diffusion based TLP models. The results of the research done will be presented and the limitations of current diffusion based TLP models will be discussed.
Ni based superalloys Waspalloy and Inconel 738 were brazed with Nicrobraz 150 filler alloy at different temperatures for various lengths of time. As the brazing temperature increased the time required to achieve isothermal solidification decreased. However, beyond a critical temperature, Tc, the time required to produce single phase solid in the brazed joint by isothermal solidification increased. This is contrary to the current diffusion based brazing models. The results, and short comings of the current diffusion brazing models are discussed.
