Ni-base alloy DZ468 has been joined by transient liquid phase bonding technique with a newly developed Co-based filler. The microstructures of the Co-base filler and the joint, the effects of heat treatment on microstructure and hardness of the joint have been investigated by various experimental methods. Results show that the Co-base filler consists of γ, M2B, M5B3 and M23B6 phases. Because of the interdiffusion between the base metal and the filler, γ, MC, M5B3 and M23B6 phases are formed in the bonding zone. And localized liquidation of substrate occurs in the diffusion affected zone, with MC and M3B2 precipitating in this area. During heat treatment, the volume of the intermetallic phases in the bonding zone resulting from incomplete isothermal solidification decreases obviously. On the contrary, the width of the diffusion affected zone increases at the solution stage and subsequently decreases at the aging stages.

•With decreasing Ti content of DZ125L, the separation temperature of γ′ decreased.•Lowering Ti content in DZ125L resulted in free crack casting blades.•DZ125L alloy needs much lower Ti/Ta ratio to achieve good castability.Directionally solidified DZ125L alloys of various Ti content were developed by low segregation technology. The microstructure, mechanical properties and castability of directionally solidified superalloy DZ125L were investigated. With decreasing Ti content in DZ125L alloy, the size, volume fraction and separation temperature of γ′ decreased. While the tensile strength and rupture life of directional solidified cylindrical samples is also obviously decreased. Lowering Ti content in alloy resulted in free hot cracking casting blades. Compared with IN792 alloy, DZ125L alloy needs much lower Ti/Ta ratio to achieve good castability.