Additive Manufacturing (AM) Capability Development - Production of Fine-Grained, Isotropic Microstructures in Gas Metal Arc- Directed Energy Deposition (GMA-DED...

The Naval Nuclear Laboratory (NNL) is seeking methods capable of producing fine-grained, isotropic microstructures in gas metal arc-directed energy deposition (GMA-DED) additive manufacturing (AM) builds. This capability is of interest to enhance material properties and ultrasonic inspection ability. The long dendritic grains in welds and GMA-DED builds are challenging for ultrasonic waves to penetrate (and penetration is direction-dependent), which could limit widespread use of the GMA-DED AM technique for use of engineering components. Large grains can lead to lower than desired yield strength as well as direction-dependent properties such as strength, ductility, and fatigue resistance. Approaches have been reported in the literature to promote fine-grained and isotropic microstructures in welds and GMA-DED builds. Applying force through peening, rolling, or other means can promote recrystallization during subsequent passes or layers. Use of magnetic or ultrasonic means to ‘stir’

the weld pool and disrupt formation of large dendrites or grains has also been studied. Addition of second phase particles to promote nucleation of dendrites or grains is another method that has been studied. These or other methods are of interest if they can be successfully applied to promote fine-grained and isotropic microstructures in GMA-DED builds and welds. NNL is interested in methods that can (eventually) be applied for engineering scale parts in a production environment, not solely for use on demonstration-sized specimens in a laboratory (though proof of concept work on smaller builds in a laboratory are of interest for initial phases of a project). Considerations of interest include repeatability and reliability of the method, plus any impacts on build productivity and cost. Materials of primary interest are Type 316L stainless steel or Alloy 625 though developmental work on other materials is of interest. NNL is interested in proposed solutions that can 1) prove the concept of an approach, 2) produce isotropic and fine-grained material verified through microstructure studies, 3) be scaled to engineering sized parts to follow. In addition, the material properties for builds employing the proposed solution must be tested in multiple orientations to demonstrate effects on strength, ductility, and ultrasonic wave propagation.