APPLICATION OF ULTRA FINE GRAIN ALLOY 718 FORGING BILLET

Alloy 718 has been frequently used for aerospace applications where excellent high temperature strength and resistance to fatigue are required. Thermomechanical processing plays a vital role in controlling the microstructure and properties in this alloy. The effect of a “delta dump” process during billet conversion on the thermomechanical response of an Alloy 718 hot die forging is presented. A billet with an essentially uniform microstructure of ASTM 9 grain size was produced and was ultrasonic inspected to a 0.4mm (1/64in.) FBH. A typical aircraft engine contoured disk was hot die forged from the ultra fine grain billet, sectioned, and the effect of direct age and solution heat treatment at various temperatures from 1750°F-19000F plus age on mechanical properties was studied. The microstructural changes were characterized using optical microscopy, SEM, and quantitative metallographic techniques. Mechanical properties are presented and compared to changes in both grain size and delta content It is shown that the “delta dump” process can be used to improve billet quality and ultrasonic inspectability and that mechanical properties of forgings made from this billet can be optimized using an appropriate solution heat treatment temperature.