Abstract: Systems and methods for transient liquid phase bonding are described herein. Embodiments of these systems and methods utilize sandwich interlayers to produce stronger, more homogeneous bonds than currently possible. These sandwich interlayers comprise a middle bonding layer sandwiched between two outer bonding layers. The middle bonding layer comprises a different composition, and may even comprise a different form, than the outer bonding layers. In embodiments, these sandwich interlayers may be used to join a single crystal material to a polycrystalline material to make a gas turbine engine component, such as an integrally bladed rotor.