Search for: All records

Abstract Gas metal arc directed energy deposition (GMA-DED) has potential for the power generation industry to reduce both time and cost since larger and more complex part geometries can be constructed compared to the typical subtractive methods. The performance of GMA-DED builds can be influenced by the deposition method, resulting microstructure, and formation of defects or secondary phases in the final component. Previous work in the literature evaluated the mechanical properties of GMA-DED builds for a range of austenitic stainless steels, however there is limited data on the high temperature mechanical behavior. This work evaluated the high temperature creep properties of GMA-DED builds constructed with type 316H, 316L, 316LSi, and 16-8-2 stainless steels at 650 °C, 750 °C and 825 °C. The alloy with longest time to rupture for a given stress varied depending on test temperature. Creep damage accumulation at grain boundaries was observed along with grain boundary precipitates which likely aided in damage accumulation. Evaluating the creep properties with the Larson-Miller parameter showed the majority of results fell within the scatter band of creep performance for wrought 316 alloys, indicating the GMA-DED process may be suitable for use in advanced energy systems. 

The performance of a newly developed multiprincipal-element alloy (MPEA) filler metal for brazing of nickel-based superalloys was directly compared to a conventional boron- and silicon-suppressed filler (BSSF) metal. The comparison was demonstrated on an Alloy 600 substrate with a brazing temperature of 1200°C. Single-phase solidification behavior and the absence of boron and silicon in the MPEA led to a joint microstructure devoid of eutectic constituents or brittle phases in brazes employing this filler metal. In the brazes using the conventional BSSF metal, incomplete isothermal solidification and subsequent athermal solidification of the residual liquid resulted in large particles of a chromium-rich boride phase distributed throughout the microstructure. Tensile testing of brazed butt joints at both room temperature and 600°C testing conditions demonstrated that the MPEA joints exhibited total ductility values at least one order of magnitude greater than that of BSSF joints, but they showed comparable yield strengths in both testing conditions. Fractographic assessment confirmed that boride phases nucleated cracks and resulted in brittle failure in the BSSF joints, while the MPEA joints exhibited extensive ductile microvoid coalescence. Fine-scale porosity and oxide inclusions may be the dominant factors limiting the overall ductility observed in the MPEA brazes.