Application of direct aging to Allvaco 718Plus (TM) alloy for improved performance

Direct aging can result in significant improvement in mechanical properties of many wrought Ni-base superalloys. Its effectiveness is closely related to hot working and aging conditions and is also alloy-dependent. This process is most often used with gamma" rather than gamma' strengthening alloys. Allvac (R) 718Plus (TM) alloy is predominantly a gamma' strengthening alloy which shows excellent mechanical properties and high thermal stability up to 704 degrees C in the solution treated and aged condition. It was uncertain if direct aging could be effective in this alloy. A test program was initiated to explore if direct aging could improve the alloy's performance and to determine the optimum process conditions. The variables evaluated included forging temperature, forging reduction, forging heating time and post-forging cooling rate. Mechanical tests and microstructural study after different direct aging treatments demonstrated that direct aging is feasible at a production scale for alloy 718Plus and a significant improvement in performance can be achieved under well-controlled conditions. The mechanism responsible for such improvement is briefly discussed.