Transient liquid phase bonding of intermetallics

The present work was undertaken to examine the applicability of transient liquid phase bonding to structural intermetallics. This research was based on an investigation of the mechanisms governing microstructural development in the joint and adjacent substrates during the joining process. The bonding systems investigated included polycrystalline NiAl/Cu/Ni, polycrystalline NiAl/Cu/superalloys (Martin-Marietta (MM)-247, Inconel (IN) 718 and Nimonic 90), single-crystal NiAl (with 1.5 at % Hf) joined to MM-247 using different filler metals (Cu foil, powder filler metal and electro-plated thin Cu film), and martensitic NiAl joined with martensitic NiTi using Cu foil and specially designed powder filler metals.; In polycrystalline NiAl/Cu/Ni bonds, the mechanism of isothermal solidification is considered. Changes in the microstructure of the bond centerline due to element redistribution are discussed. The precipitation of both {dollar}L1sb2{dollar} type {dollar}gammaspprime{dollar} and B2 type {dollar}beta{dollar} phase at the joint centerline is investigated. The formation of martensitic {dollar}L1sb0{dollar} type NiAl is also examined. The mechanical properties of the joints are investigated using shear strength and microhardness tests.; In TLP bonding of polycrystalline NiAl with MM-247, both the epitaxial growth of the {dollar}beta{dollar} phase NiAl into the joint and the formation of non-epitaxial {dollar}beta{dollar}-phase layers are considered. The formation of second-phases, including the {dollar}gammaspprime{dollar} phase, carbides, and {dollar}sigma{dollar}-phase intermetallics is also examined. Bond-line and adjacent substrate microstructures for the NiAl/Cu/MM-247 bonds are correlated with joint mechanical properties determined by room temperature shear testing.; Single-crystal NiAl (1.5 at % Hf)/Cu/MM-247 joints are examined and compared with polycrystalline NiAl/Cu/MM247 joints. The effect of Hf on the microstructure of joints is investigated. The influence of different filler metals (i.e., wide-gap powder filler metal and electro-plated thin film filler metal) on the joining process is also considered.; In TLP bonding of martensitic NiAl with martensitic NiTi, the formation Ti depletion region was observed while using Cu foil as the filler metal. Alternative filler metals were successfully used to solve this problem.; According to the experimental results, standard TLP bonding models cannot be applied to the bonding systems in this research. The influence of second phase formation on TLP models is discussed.