Microstructure and Interfacial Characteristics of Inconel 625-Ti6Al4V Bimetallic Structures Produced by Directed Energy Deposition

Inconel 625 superalloy was deposited on Ti6Al4V by Directed Energy Deposition (DED) additive manufacturing process to develop a bimetallic structure with unique properties combining the benefits of both alloys. The processing ability and effect of process parameters on the interface and microstructure of the bimetallic structure were studied. A 1 kW diode laser and a coaxial nozzle were used. Single-track and multi-track depositions were carried out to understand the influence of process parameters on the microstructure and interface of the Inconel 625-Ti6Al4V bimetallic structure. The process parameters of DED, such as laser power (400, 600 and 800 W), laser scan speed (400, 600 and 800 mm/min) and powder feed rate (2, 3 and 4 g/min), were varied to investigate their influence on melt-pool temperature, microstructure, elemental composition, phase evolution and microhardness. Microstructure studies revealed the formation of lamellar, columnar dendritic, equiaxed and flower-shaped eutectic structures in the bimetallic structures. Phase analysis indicated the evolution of phases as follows: alpha-Ti + beta-Ti -> alpha-Ti + beta-Ti + Ti2Ni -> beta-Ti + Ti2Ni + TiNi + gamma-Ni. It is found that there is a significant influence of process parameters on the formation of intermetallic phases, which are responsible for crack formation and debonding in the bimetallic structures. The lesser gradient in microhardness across the bimetallic interface was achieved at a higher laser scan speed, which can also help minimise the formation of intermetallic phases to achieve better interface bonding in the bimetallic structures.

Automated summary

Inconel 625 superalloy was deposited on Ti6Al4V using Directed Energy Deposition (DED) additive manufacturing process to create a bimetallic structure with unique properties. The study investigated the effect of various process parameters on the microstructure and interface of the bimetallic structure. Different laser power, laser scan speed, and powder feed rate were used to study their influence on the melt-pool temperature, microstructure, elemental composition, phase evolution, and microhardness. The results showed the formation of various structures and phases, with intermetallic phases affecting the interface bonding.