High-value metal alloys for additive manufacturing (AM)

Metal additive manufacturing (AM) has grown to become a critical and innovating strategic tool for the aerospace and defense (A&D) sectors, due in large part to developments in materials science. Entering into this new wave, materials are now designed for the AM process and repeatability, compared to previous materials intended for forging or casting. These advanced materials can meet customer requirements and allow for more design freedom and complex geometries. One company focused on further developing these materials to meet rigid design criteria and overcome today’s aerospace challenges is Allegheny Technologies Inc. (ATI).

ATI creates new specialty materials for 3D printing high-performance aero engine and airframe structures. “What we’ve found is that, by looking at these alloys and applying them to additive manufacturing, they actually solve a lot of the problems,” says Brian Morrison, director, AM at ATI. “As we listen to our customers, they’re often concerned that metal alloys such as titanium 6-4 [Ti-6Al-4V] create way too much residual stress. Therefore, building parts with it that are dimensionally tolerant can be challenging. Ti-6Al-4V doesn’t always have the strength requirements that customers need for their application.”

To overcome these barriers, the specialty materials company has shifted its focus and is developing Titan 23, a high-strength titanium alloy. Titan 23 has higher strength capability than Ti-6Al-4V, with similar elongation and capabilities that solve common problems such as high residual stress. While developing this material, ATI found that its residual stresses are much lower, meaning the dimensional accuracy of a finished part is much closer to the computer-aided design (CAD) model.

Titan 23 provides the necessary dimensional tolerance and strength requirements when developing complex engine parts or structural parts for aircraft.

Highlighting more of the alloy’s benefits, Richard Merlino, senior director of AM at ATI, goes on to explain, “In higher temperature situations, it does have slightly better temperature resistance. For example, if the designer is just out of the temperature regime of Ti-6Al-4V and is forced to transition to nickel, which is dramatically heavier, this might give that little extra boost that allows you to use titanium materials, which give you the required weight savings and the same temperature resistance.”

The Titan 23 alloy has increased alpha and beta stabilizer content which allows it to improve room temperature strength, thick section hardenability, and fatigue life.

Further alloy advantages

Another alloy family, titanium aluminide, is very hard to process through traditional means, such as casting or machining. Through AM however, titanium aluminide is being used for low pressure turbine blades and next-generation jet engines. They are replacing what would have been nickel castings to deliver significant weight savings.

These alloys offer further benefits compared to traditional alloys and provide the flexibility to design more complex shapes than what’s possible with traditional manufacturing. According to Merlino, materials with minimal distortion can maintain complex geometries. Ultimately, it results in a better-performing part because it either provides the same performance with less weight, or in a fluid flow application, offers increased fluid flow with possibly lower pressures.

“These benefits are definitely recognizable, so that if an alloy gives more flexibility in printing, which allows the designer to get more creative on the design, that should allow for better performance,” Merlino adds.

Impact on A&D industries

There are several environmental, financial, and security advantages of using AM in the A&D industries, implying how these materials could also propel the industries forward.

Due to the big reduction in material used in AM versus traditional manufacturing, users will see immediate benefits.

“For example, subtractively processing 20 lb of stock to a 1 lb part. Now, for a 1 lb part, we might use 1.2 lb of material in AM; you’re going to see benefits,” Morrison explains. “Another noticeable impact in aerospace is that AM parts are going into service for potentially 20 years plus.”

For commercial aircraft, weight savings will be evident throughout its entire 20-year life cycle. This will reduce carbon emissions, too. Morrison and Merlino say for designers to truly unleash the power of AM, they must get more comfortable with the technology to design enough performance into the product that AM makes sense financially. AM is still not as fast as casting or machining, so designers will have to make parts with enough complexity to justify using it. AM’s value is growing as people get more comfortable with it and recognize its capabilities.

AM is also helping to advance security within the Department of Defense (DOD), with more tools being developed for IT and infrastructure that allow companies (such as ATI) to produce a part and give the military the confidence that it was produced according to specifications. This is achieved through remote monitoring and guaranteeing that the model was printed correctly on the machine.

“You’re going to become more confident that we printed the right part, and we have validation in our facility and by the customer that shows it was done correctly,” Morrison adds.

Another key focus on the defense side for AM is sustainability. Being able to produce parts on-demand to keep warfighters in the battle is a major advantage. For example, if aging platforms need replacement parts, you can use the strength of AM if the supply chain has gone out of business, Morrison adds.

Looking toward the future of AM and developments in materials science, Morrison and Merlino predict even more possibilities. They believe that as everyone becomes more comfortable with the process, we’re also going to see new material development, which will unleash the ability to produce more complex parts, use more complex alloys, and open new opportunities for AM.

ATI (Allegheny Technologies Inc.)

About the author: Michelle Jacobson is the assistant editor of AM&D. She can be reached at 216.393.0323 or mjacobson@gie.net.