This study focuses on the transient liquid phase (TLP) bonding of DD5 single-crystal superalloy to CrCoNi-based medium-entropy alloy (MEA) using a BNi-2 filler alloy.The microstructure and mechanical proper-ties of the TLP-bonded DD5/MEA joint were evaluated,and the microstructural evolution mechanism was investigated.The formation of the isothermal solidification zone (ISZ) depended on the diffusion of the melting-point depressants (Si and B elements) from the liquid filler into the DD5 and MEA substrates,as well as the dissolution of the substrates.Boron diffused along the y channel of DD5 and reacted to form M5B3 boride,herein referred to as the diffusion-affected zone (DAZ Ⅰ).Similarly,the Cr5B3 boride precipitated in the Ni-rich MEA matrix adjacent to the MEA substrate (i.e.,DAZ ll).Additionally,a coher-ent orientation of[0]BCT //[011]FCC and (002)BCT//(200)FCC was detected between M5B3 boride with a body-centered tetragonal (BCT) structure and the face-centered cubic (FCC) matrix.The performance of the joint was dominated by the properties of the bonding seam.As the bonding time increased from 20 to 80 min,the athermal solidification zone (including eutectic microstructure) was gradually replaced by the ISZ exhibiting excellent plastic deformation capability,and the shear strength of the joint was im-proved.The maximum shear strength (752 MPa) was achieved when the eutectic-free joint was bonded at 1050 ℃ for 80 min.The fracture morphology revealed a mixture mode,indicating the initiation of cracks in the DAZ Ⅱ,mainly propagating in the ISZ,and passing through the DAZ Ⅰ.