Experimental and theoretical investigations of transient liquid phase bonding of nickel based materials
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This thesis reports theoretical and experimental investigations carried out to better understand the effect of process parameters on the microstructure of transient liquid phase (TLP) joint. The theoretical investigations were carried out using analytical and numerical models to simulate base metal dissolution and isothermal solidification stages of the TLP bonding process. The experimental investigation was carried out by using standard metallographic technique to study the microstructure of bonded materials using optical and Scanning Electron Microscopes. Deviation from parabolic relationship between solid/liquid interface migration and holding time during TLP bonding is suggested as a new alternate phenomenon responsible for the anomalous increase in processing time required to produce eutectic microconstituent free joint with increase in bonding temperature. The results of TLP joining of commercial pure nickel using a Ni-P filler alloy showed that an increase in bonding temperature would be beneficial provided that sufficient holding time is allowed for complete isothermal solidification of liquated insert. Otherwise, an increase in bonding temperature may result in formation of thicker deleterious eutectic along the TLP joint. Furthermore, it was observed that the joint centerline eutectic product and interface second phase particles that form during TLP bonding of Inconel 738 using Ni-P filler can be significantly reduced by post bond heat treatment. The effectiveness of this approach, however, requires proper selection of heat treatment temperature above Ni-P binary eutectic temperature.