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Karnesky, R.A.; Chao, P.; Buchenauer, D.A. |
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Hydrogen isotope permeation and trapping in additively manufactured steels |
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Conference Article |
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2017 |
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ASME Pressure Vessels and Piping Conference |
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6A |
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V06AT06A019 |
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Additively manufactured (AM) austenitic stainless steels are intriguing candidates for the storage of gaseous hydrogen isotopes. Complex vessel geometries can be built more easily than by using conventional machining options. Parts built with AM steel tend to have excellent mechanical properties (with tensile strength, ductility, fatigue crack growth, and fracture toughness comparable to or exceeding that of wrought austenitic stainless steel). However, the solidification microstructures produced by AM processing differ substantially from the microstructures of wrought material. Some features may increase permeability, including both some amount of porosity and a greater amount of ferrite. Because the diffusivity of hydrogen in ferrite is greater than in austenite (six orders of magnitude at ambient temperature), care must be taken to retain the performance that is taken for granted due to the base alloy chemistry. Furthermore, AM parts tend to have greater dislocation densities and greater amounts of carbon, nitrogen, and oxygen. These features, along with the austenite/ferrite interfaces, may contribute to greater hydrogen trapping. We report the results of our studies of deuterium transport in various austenitic (304L, 316, and 316L) steels produced by AM (via either powder bed fusion or blown powder methods). The hydrogen permeability (an equilibrium property) changes negligibly (less than a factor of 2), regardless of chemistry and processing method, when tested between 150 and 500 °C. This is despite increases in ferrite content up to FN=2.7. However, AM materials exhibit greater hydrogen istotope trapping, as measured by permeation transients, thermal desorption spectra, and inert gas fusion measurement. The trapping energies are likely modest (<10 kJ/mol), but may indicate a larger population of trap sites than in conventional 300-series steels. |
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NU @ karnesky @ karnesky_hydrogen_2017 |
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11517 |
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