Which superalloy grades are best for aerospace free forging?

High-Strength Nickel-Based Alloys for Critical Structures

For aerospace free forging, several nickel-based superalloys are preferred due to their exceptional combination of high-temperature strength, creep resistance, and forgeability. Inconel 718 is arguably the most widely used grade of Inconel. It offers an excellent balance of high yield and tensile strength up to about 650°C (1200°F), good fatigue life, and—critically for forging—it is one of the most weldable and forgeable superalloys due to its sluggish age-hardening response, which reduces the risk of cracking during processing.

Elevated Temperature Solutions for Turbine Components

For applications requiring performance at higher temperatures, such as turbine disks and shafts, Nimonic 263 and Nimonic 901 are excellent choices. Waspaloy is another industry standard for high-pressure turbine disks, capable of sustaining high mechanical loads at temperatures up to 815°C (1500°F). These alloys maintain their strength through solid solution strengthening and gamma prime precipitation, but they require more precise control over the forging temperature and subsequent heat treatment to achieve the desired microstructure.

Advanced Forging Alloys for Next-Generation Engines

Pushing the temperature and performance envelope further, alloys like Rene 41 and Rene 88 DT are used. Rene 41 offers very high strength and oxidation resistance up to 980°C (1800°F) but is notoriously difficult to forge and weld due to its high susceptibility to strain-age cracking. Rene 88 DT is a powder metallurgy superalloy specifically designed for forged turbine disks, offering superior fatigue capability and temperature resistance. However, it often relies on powder metallurgy processing before forging to ensure chemical homogeneity.