THE PRECIPITATION PROCESSES AND MECHANICAL PROPERTIES OF AGED INCONEL 718 ALLOY AFTER ANNEALING

Inconel 718 is a precipitation hardenable nickel-iron based superalloy. It has exceptionally high strength and ductility compared to other metallic materials. This is due to intense precipitation of the gamma' and gamma strengthening phases in the temperature range 650-850 degrees C. The main purpose of the authors was to analyze the aging process in Inconel 718 obtained in accordance with AMS 5596, and its effect on the mechanical properties. Tensile and hardness tests were used to evaluate the mechanical properties, in the initial aging process and after reheating, as a function of temperature and time respectively in the ranges 650 degrees-900 degrees C and 5-480 min. In addition, to link the mechanical properties with the microstructure transmission microscopy observations were carried out in selected specimens. As a result, factors influencing the microstructure changes at various stages of strengthening were observed. The authors found that the gamma'' phase nucleates mostly homogenously in the temperature range 650-750 degrees C, causing the greatest increase in strength. On the other hand, the gamma' and delta phases are formed heterogeneously at 850 degrees C or after longer annealing in 800 degrees C, which may weaken the material.