Superalloys in AM a Game Changer

With such material considerations in mind, aviation, aerospace and heavy industries have begun looking at additive manufacturing (AM) of superalloys as potential game-changing technology. AM can deliver complex, previously unmanufacturable, innovative designs that boost product performance while reducing supply-chain delays and associated production costs. Particularly in high-temperature gas turbines—traditionally assemblies of tens to hundreds of parts including tubes, flow paths and sheet metal structures that must be formed and welded to other components—AM presents attractive opportunities for design simplification and part consolidation.

Given the desirable qualities achievable with superalloys, companies beginning to explore the potential of AM are asking for equipment—or access to contract manufacturers running advanced industrial AM systems—that can handle such material. 
AM machine providers, in turn, are embracing the opportunity to use their technology to solve problems encountered by engineers when using traditional manufacturing to make high-performance, mission-critical components from superalloys. Response to this demand, however, runs up against inherent challenges.

Fine-Tuning the Process

Metal AM, essentially a micro-welding operation in which a geometry-directed laser beam melts ultra-thin layers of material sequentially to build up a 3D part, is impacted by material purity. While many OEMs have their own recipes for metal powder, quality standards allow for a range of certain elements within an alloy—a superalloy formula may contain more or less oxygen or carbon. The lower carbon content in HastX leads to better results; the most successful print runs occur when material choice controls for that.

Another issue: HastX can create base-metal soot or condensate during the laser-sintering process, fouling the surrounding powder. Soot landing directly on the powder bed can cause issues with energy absorption. Or, should the gas flow used to flush out the chamber during AM not completely evacuate the soot, the chamber volume can become loaded with airborne condensate that blocks the laser beam. Such occlusion changes the amount of power delivered to the powder bed and interferes with the welding process.

To ensure clean gas flow around a part being sintered from HastX, next-gen AM systems operate in an argon-gas environment that keeps oxygen levels extremely low. While other systems use nitrogen, argon typically delivers better results throughout a build.  

Lastly, AM of HastX can lead to hot cracking—less of a problem than with some other superalloys but still something that requires attention, particularly when building thin-walled, high-heat structures. Here, precise directing of the thermal energy of the laser is key, due to how the active melt pool cools and solidifies during an AM build. Cooling and solidification depend greatly on what’s around the build—usually metal on one side and powder on the other. An insulator, powder conducts heat poorly; as a layer cools, that thermal energy predominantly transfers into the newly created thin metal walls. Too much thermal energy in the wrong place can weaken and warp the structure. Therefore, laser power must be applied at the precise location and strength every millisecond—an attribute of the in-process monitoring and feature-specific parameter control provided by some AM systems. 

Matching the Material to the Application

Even given the variety of challenges inherent in matching materials to production processes, many AM-machine makers now have portfolios of as many as 40 different materials. Yet, in many cases the cost of printing does not align with the material chosen. The application space also can be limited.

Suppliers of newer AM systems have prioritized customer and market considerations, and consciously limited the range of applications for which they’ve developed their exacting AM processes and accompanying software. Capabilities such as support-free manufacturing (at angles now down to fully horizontal overhangs) of extremely thin-walled parts align well with high-temperature applications involving fluid flow and heat exchange. This, in turn, dovetails well to the production of parts and components made from HastX and other superalloys. 3DMP

See also: Velo3D

Technologies:

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