Microstructure and mechanical properties of heat treatment laser solid forming superalloy Inconel 718

With the development of additive manufacturing technology of metal, laser solid forming (LSF) has become an important fabricating method for high performance and complex Inconel 718 alloy components. However, there still exist a certain microsegregation and a large uneven distribution of residual stress in as-deposited Inconel 718 alloy due to rapid heating and cooling in LSF. Heat treatment is a necessary method for further improving the microstructure and mechanical properties. In this work, the microstructure and mechanical properties of LSFed Inconel 718 alloy heat treated with high temperature solution, δ phase aging and double aging treatment was investigated, the dislocation configuration of heat treated LSFed Inconel 718 alloy was characterized. It is found that the recrystallization occurs after the heat treatment, which leads to the transition from the columnar grain in the as-deposited to the equiaxed grain. Laves phase is dissolved completely after the heat treatment, and the needle δ phase and the γ″ phase precipitate along the grain boundary and in the g phase matrix, respectively. The strength, elongation and reduction of area of the heat treated Inconel 718 alloy satisfy the wrought standards. There are two kinds of interactions between the dislocation and the γ″ phase, the shearing mechanism and the Orowan bypass mechanism, which play the dominant role corresponding to the lower and the higher distribution density of γ″ phase, respectively. Additionally, the dislocations pile up at the δ phase owing to the larger size of the δ phase in the heat treated Inconel 718 alloy compared with that in the wrought. The dislocation glide can be also hindered by carbide due to the pinning and drag effect.