Grain boundary precipitates in Inconel 718 and ATI 718Plus are important to control during hot working processes, since they can control the grain size. Precipitating excessive or insufficient amounts can be detrimental to the final component. Therefore, it is important for manufacturers to understand the formation and kinetics of grain boundary precipitation and the effect this has on mechanical properties. This review considers the background of grain boundary precipitation, including the effect of the thermal stability of γ and γ phases. In addition, the effect of stress on the grain boundary phases and their precipitation kinetics in different conditions are also included. Also, the impact of grain boundary precipitation on the mechanical properties is explored. ARTICLE HISTORY

Abstract. ATI 718Plus components are manufactured by forging a wrought billet in stages to obtain the desired geometry and microstructure. Parts are then heat treated to optimized proportions of ' and phases. phase is a plate-like phase that precipitates on the grain boundaries of ATI 718Plus, similar to phase in Inconel 718. However, the complete kinetic behaviour of phase precipitation during forging and heat treatment is still not fully understood. This paper investigates the effects of strain hardening on phase precipitation kinetics in ATI 718Plus. This is achieved through the use of isothermal hot compression tests and heat treatment. Strain hardening was found to affect the precipitation kinetics considerably. The results reported are a contribution to a fuller understanding of this important process.