Effects of transient liquid phase bonding on corrosion performance of a single crystal aerospace superalloy
Transient Liquid phase bonding (TLP) has evolved as a viable method of joining difficult-to-weld superalloys with potential of producing joints with comparable mechanical properties to the base material. Although the high temperature properties of aerospace superalloys have been studied extensively, there is little information on the corrosion behaviour of these special class of materials that had been subjected to TLP bonding. In this work, electrochemical assessment of the corrosion behaviour of TLP bonded nickel-based superalloy was performed. Microstructural evaluation of the TLP bonded joint revealed the presence of a centreline eutectic when isothermal solidification was not completed and the corrosion resistance increased with a decrease in this eutectic width. The use of a composite interlayer produces TLP joints with smaller eutectic size and results in complete isothermal solidification in shorter processing time. Complete isothermal solidification, achieved with the composite interlayer, results in a uniform chromium distribution in the joint centre and produced a corrosion performance similar to the as-received cast base metal. It was found that aside from the mere presence of chromium, which is widely recognised as necessary for corrosion resistance, its uniform distribution within the joint region is imperative for achieving adequate corrosion resistance in TLP joints.
Transient Liquid Phase Bonding, Corrosion, Superalloys, Potentiodynamic Polarization