Microstructure and mechanical properties of forging-additive hybrid manufactured Ti–6Al–4V alloys

The forging-additive hybrid manufacturing technology has combined the advantages of traditional manufacturing in efficiency and cost with those of additive manufacturing in flexibility and rapid prototyping, thus can provide an effective solution for the efficient forming of large and complex components. In this kind of manufacturing technology, the heat affected zone (HAZ, also called as bonding zone) between the wrought substrate zone (WSZ) and the laser deposition zone (LDZ) is the key to the properties of final components. In this study, the powder-feeding laser additive manufacturing technology was employed to deposit bulk samples on a wrought Ti–6Al–4V substrate containing bimodal microstructures. The microstructures and mechanical properties of hybrid manufactured Ti–6Al–4V alloys were studied with emphasis on the HAZ. The results show that, due to the different history of thermal, a graded microstructure was formed from the bottom to the top of HAZ. The bimodal microstructure at the bottom-HAZ gradually transformed to a mixed structure contained equiaxed α, lamellar α, and a large number of secondary α in the middle-HAZ, while the top-HAZ exhibits Widmanstätten structures consisting lamellar α and the so-called ghost structures due to the insufficient diffusion of alloying elements. The measurement of mechanical properties shows that, the sample with bonding zones presents higher tensile strength and yield strength, but lower elongation than those without bonding zones (WSZ or LDZ). The fracture positions of all samples with bonding zones are in WSZ and far away from HAZ, indicating a better strength of bonding zone than that of the wrought substrate and the laser deposition part due to the formation of secondary α and fine lamellar α in HAZ.