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- Synthesis of Non-Cubic Nitride Phases of Va-Group Metals (V, Nb, and Ta) from Metal Powders in Stream of NH3 Gas under Concentrated Solar RadiationPublication . SHOHOJI, Nobumitsu; Oliveira, F. A. Costa; Galindo, José; Rodríguez, José; Cañadas, Inmaculada; Fernandes; Rosa, Luis G.Using a high-flux solar furnace, loosely compacted powders of Va-group transition metal (V, Nb, and Ta) were reacted with stream of NH3 gas (uncracked NH3 gas) being heated by concentrated solar beam to a temperature (T) range between 600 and 1000 °C. From V, sub-nitride V2N (γ phase) and hypo-stoichiometric mono-nitride VN possessing fcc (face-centered cubic) crystal lattice structure (δ phase) were synthesized. On the other hand, in the reaction product from Nb and Ta, hexagonal mono-nitride phase with N/M atom ratio close to 1 (ε phase) was detected. The reaction duration was normalized to be 60 min. In a conventional industrial or laboratory electric furnace, the synthesis of mono-nitride phase with high degree of crystallinity that yield sharp XRD peaks for Va-group metal might take a quite long duration even at T exceeding 1000 °C. In contrast, mono–nitride phase MN of Va-group metal was synthesized for a relatively short duration of 60 min at T lower than 1000 °C being co-existed with lower nitride phases.
- Expansion of additive-manufactured tubes: deformation and metallurgical analysisPublication . Pragana, João; Rosa, Luis G.; Bragança, Ivo; Silva, Carlos; Martins, PauloHerein, the mechanical and metallurgical feasibility of integrating tube end-forming operations with additive manufacturing is investigated. The work makes use of wire-arc additively manufactured AISI 316L stainless steel preforms that are subsequently machined into tubes and expanded with a tapered conical punch. Experimental measurements of force, surface strains, thickness, and microhardness combined with microstructure observations and fractography of the fractured surfaces are utilized to characterize plastic deformation and formability limits of the additively manufactured tubes and understand the main differences against the results obtained from commercial wrought tubes of the same material. Results show that the material deformation characteristics, namely, the evolution of microhardness along the expanded tube length, and the formability limits by necking and fracture, are strongly influenced by the columnar microstructure originated by a noncyclic dendritic growth aligned with the building direction. Still, results demonstrate that the additively manufactured AISI 316L tubes are ductile enough to be successfully included in hybrid additive manufacturing routes.