Several zirconium alloys with differing weight percentages of Cr, Fe, Cu, and Mo were exposed to fl owing, pure supercritical water at 500°C for up to 150 days in an effort to determine their corrosion behavior for consideration in the supercritical water reactor. The weight gains of the alloys were measured, and oxides were characterized after various times. The test results showed a wide range of corrosion behavior depending on the alloy composition and process temperature. The alloys most resistant to corrosion were those containing Cr and Fe, three of which showed protective stable oxides, low corrosion rates, and no breakaway behavior. The ZrCr, ZrCu, ZrMo, and ZrCuMo alloys all exhibited high corrosion rates and nonprotective oxides. Analysis of the oxide layer showed that the oxide consisted mostly of monoclinic zirconia (ZrO 2). The structure of the oxide-metal interface in the fi ve protective alloys exhibited characteristics that were also seen in protective oxides formed at low temperature, especially the presence of a suboxide layer and an intense (002) T peak at the interface, indicating the presence of a highly oriented tetragonal phase associated with the protective oxide. The change in corrosion kinetics from cubic to linear was directly linked to the size and density of cracks in the oxides.
In recent years, magnetocaloric materials have been extensively studied as materials for use in alternative cooling systems. Shaping the magnetocaloric material to thin-walled heat exchanger structures is an important step to achieve efficient magnetocaloric cooling systems. In the present work, experimental investigations were carried out on the heat treatment of LaFe11.4Si1.2Co0.4 alloy processed by Laser Beam Melting (LBM) technology. Due to the rapid solidification after melting, LBM results in a refined micro structure, which requires much shorter heat treatment to achieve a high percentage of magnetocaloric 1:13 phase compared to conventional cast material. The influence of the heat treatment parameters (temperature, time, and cooling rate) on the resulting microstructure has been extensively studied. In addition to the conventional heat treatment process, induction technology was investigated and the results were very promising in terms of achieving good magnetocaloric properties after short-time annealing. After only 15 min holding time at 1373 K, the magnetic entropy change (∆S) of -7.9 J/kg/K (0–2 T) was achieved.
Laser additively manufactured duplex stainless steels contain mostly ferrite in the as-built parts due to rapid solidification of the printed layers. To achieve duplex microstructures (ferrite and austenite in roughly equal proportions) and, thus, a good combination of mechanical properties and corrosion resistance, an austenitic stainless steel powder (X2CrNiMo17-12-2) and a super duplex stainless steel powder (X2CrNiMoN25-7-4) were mixed in different proportions and the powder mixtures were processed via PBF-LB/M (Laser Powder Bed Fusion) under various processing conditions by varying the laser power and the laser scanning speed. The optimal process parameters for dense as-built parts were determined by means of light optical microscopy and density measurements. The austenitic and ferritic phase formation of the mixed alloys was significantly influenced by the chemical composition adjusted by powder mixing and the laser energy input during PBF-LB/M. The austenite content increases, on the one hand, with an increasing proportion of X2CrNiMo17-12-2 in the powder mixtures and on the other hand with increasing laser energy input. The latter phenomenon could be attributed to a slower solidification and a higher melt pool homogeneity with increasing energy input influencing the phase formation during solidification and cooling. The desired duplex microstructures could be achieved by mixing the X2CrNiMo17-12-2 powder and the X2CrNiMoN25-7-4 powder at a specific mixing ratio and building with the optimal PBF-LB/M parameters.
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