Effect of Aging Treatment on Microstructure and Impact Properties of IN718 Alloy Fabricated by Laser-Drected Energy Deposition

The IN718 superalloy is widely used in the manufacturing of turbine blades and other components of aerospace engines. Improving the impact performance of this alloy is of profound significance for ensuring the stable operation of related components. This work studies the effects of different aging treatments on the microstructure, δ phase precipitation, and impact performance of laser directed energy deposition IN718 alloy. The morphology and microstructural features of the impact fracture cross-section of the samples subjedted to various aging treatments were analyzed using an electron microscope and an X-ray diffraction instrument. The influence of different aging treatments on the impact performance of the IN718 alloy was elaborated in detail. The results show that after the solution-treated samples are subjected to aging treatment at 900 ℃, the δ phase nucleates preferentially at grain boundaries or twin boundaries. As the aging time prolongs, the morphology of the δ phase changes from short rods to long needles. After 900 ℃/28 h aging treatment, the volume fraction of the δ phase reaches 19.8%. The high volume fraction and needle-like δ phase reduce the impact performance of the IN718 alloy, while the granular carbides exert negligible influence on the alloy’s impact performance. The impact toughness value of the sample aged at 900 ℃ for 0.5 h is 70.7 ± 4.7 J/cm², while that of the sample aged at 900 ℃ for 28 h is only 37% of that of the 900 ℃/0.5 h sample. This findings indicate that as the aging time increases, the fracture mechanism of the impact sample changes from ductile fracture to cleavage fracture.