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BackgroundFeCrAl alloy cladding, as an accident tolerant fuel (ATF) mid-term commercial technology approach, has received extensive attention.PurposeThis study aims to investigate the effect of trace Y on the internal pressure burst and oxidation properties of FeCrAl alloy cladding.MethodsFirstly, the crystalline grain size and micro-morphologies of FeCrAl and FeCrAlY alloy cladding samples were observed by optical microscope. Internal pressure burst and high temperature oxidation tests were carried out by burst test equipment and thermo-gravimetric analyzer with a moisture generator. Then, X-ray diffractometry (XRD), scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were employed to analyze the composition of oxidation products, surface and cross-sectional micro-morphologies of FeCrAl and FeCrAlY alloy cladding samples before and after high-temperature stream oxidation and the distribution of elements on the surface oxidation products.ResultsThe results show that trace Y is mainly dissolved in the FeCrAl alloy matrix, and no Fe-Y phase is formed. The inclusion of Y do not change the burst strength and the rupture opening morphology at room temperature (RT) to 1 000 ℃, and the high-temperature steam oxidation resistance of FeCrAl alloy cladding is significantly improved by the trace Y. Under the condition of steam oxidation at 800 ℃, 1 000 ℃ and 1 200 °C for 8 h, the oxidation weight gain of FeCrAlY alloy cladding decrease by 65.1%, 60.0% and 31.5%, respectively. Compared with the single Al2O3 oxide film on the surface of FeCrAl alloy cladding, the Y-containing composite oxide film with lower internal stress, higher compactness and better adhesion with the substrate is formed on the surface of FeCrAlY alloy cladding.ConclusionsTherefore, the addition of trace Y do not change the burst properties of FeCrAl alloy cladding, however, the high-temperature steam oxidation resistance of FeCrAl alloy cladding is significantly improved.

Aiming to diminish the defects caused by high-speed pulsed GMAW (Gas Metal Arc Welding), such as lack of penetration, lack of fusion, humping and undercut, this paper proposes an improved twin-wire GMAW welding process by introducing the impact of additional shielding gas on the molten pool, and the effects of different shielding gas flowrates on the mechanical properties and microstructure of the welded seams were investigated. The purpose of introducing additional shielding gas was to use the airflow hood formed by gas injection to isolate air. The impact force generated by the jet might change the original natural solidification mode of the molten pool, which had the effect of improving weld formation and stirring the pool. The airflow hood formed during the process of the additional shielding gas jet impact welding of the molten pool might extend the protection time for the surface of the welding molten pool. The 2205 duplex stainless steel plate was used as the base material for the butt welding test, and the welded seams were subjected to a tensile test, hardness analysis, and metallographic analysis. The results indicated that as the flowrate of additional shielding gas increased in the range of 8 L/min~16 L/min, the width of the welded seam increased and the height of reinforcement decreased gradually. However, a weld seam with a lower middle region and higher sides would appear when the gas flowrate became excessively large. Under the identical welding current and for welding speeds of 160 cm/min, 180 cm/min and 200 cm/min, respectively, the joint formed under the flowrate of 12 L/min had the highest tensile strength (824.3 MPa) among the test specimens under different flowrates of 8 L/min, 12 L/min and 16 L/min. The test results indicated that the jet impact force was relatively moderate when the flowrate of the additional shielding gas was 12 L/min, and thus was optimal for the welded seam. [ABSTRACT FROM AUTHOR]

Cold metal transfer (CMT) additive manufacturing (AM) is widely used for its efficiency and low cost, in order to improve the efficiency the manufacturing,this study carried out CMT arc modes and interlayer cooling time depositions, and researched deposition stability, roughness, microstructure, and properties. Moreover, as the tensile anisotropy was a significant characteristic of arc AM, this study conducted tensile fracture metallographic test, and revealed the tensile anisotropic mechanism. The results showed that CMT mode was the most stable process, and CMT Plus Pulse (CMT+P) mode with an alternating of CMT and pulse processes had a finer grain and bigger hardness. Although an interlayer cooling time refined the grain size, it also increased the deposited time and roughness. Then, deposition efficiency of CMT+P continuous deposition was up to 87.9%, which realized the forming efficiency. The tensile fracture metallographic test indicated the deformed columnar grains were widened by horizontal stretching, and then the fracture occurred at the grain boundaries. However, no obvious grain deformation occurred under the vertical tension, and the columnar grain boundaries were the weak link of tensile fatigue. Thus, horizontal tensile strength with more grain boundaries was smaller than the vertical one. [ABSTRACT FROM AUTHOR]