Search

Structural materials used in nuclear reactor environments are subjected to coupled extremes such as high temperature, irradiation, and corrosion which act in concert to degrade their functional performance. Connecting alloy microstructure such as grain boundaries, and accumulating point defects with corrosion attack and pore morphology is critical to understanding underlying mechanisms. We uncover the compositional variations and morphology at multiple length scales in corrosion-damaged Ni-Cr alloy after exposure to oxidants in molten fluoride salts. A complex network of dense corrosion pores is detected by surface-level SEM observations. The corrosion pores take on a 1-dimensional morphology and are enriched with Ni and depleted of Cr 1–5 µm from the pore surface. STEM-EDS and 4D-STEM strain maps acquired simultaneously highlight the local variations in composition and structure of a ≤ 200 nm Cr-rich layer identified from a cross-section taken at the bottom of an isolated corrosion pore between the Ni-Cr alloy matrix and the embedded salt. However, the absence of an observed interface between the Ni-Cr alloy matrix and the FCC-structured Cr-rich layer suggests that Cr plating from the salt did not transpire. These findings support a proposed Cr lattice diffusion mechanism rather than Cr-precipitation from the salt to accommodate temperature transient conditions during sample cooling. Through the development of a 1D phase field model, these results are rationalized by formation energies for the Ni- and Cr-oxidation into the molten salt. This study reveals the locally altered microstructure caused by high temperature corrosion in non-steady-state molten salt nuclear reactor environments.

This work is a study aimed at optimizing the process of superarc metallization, with a focus on the effect of voltage on the properties of the spraying coatings. In this work, 30HGSA grade steel wire was used for the coating of 45 steel, widely used in mechanical engineering. The use of supersonic arc metallizer SX-600 allowed to obtain coatings at different voltages (32 V, 38 V and 44 V) and the same current strength. Various metallization process parameters such as material feed rate, voltage, current, distance and nozzle geometry are discussed in this paper. Using various analytical techniques including X-ray diffraction analysis, microscopy, microhardness and corrosion resistance tests, the qualities of the coatings were evaluated. Particular attention was paid to analyzing the phase composition of the coatings, porosity, substrate bond strength and tribological characteristics. It was found that the voltage during the supersonic arc metallization process has a significant effect on these characteristics. The selected optimum voltage allows to obtain dense and homogeneous coatings with improved performance properties. The results of the study revealed that the best physical and mechanical properties were exhibited by the sample processed at 38 V, which showed lower porosity and improved strength characteristics compared to the other samples. These findings can be used to improve manufacturing processes in industries such as automotive and mechanical engineering, where restoration and improved performance of worn parts is required. [ABSTRACT FROM AUTHOR]

The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic (LBE) at 200 °C is studied using electrochemical impedance spectroscopy. The structures and resistance of oxide grown on iron oxidized in air at different temperatures and durations are compared. The results show that the resistance of the oxide film increases with increasing oxidizing temperature, due to the formation of a thicker scale and fewer defects. At the same temperature (600 °C), increasing the oxidation time can also reduce the defect concentration in the oxide film and improve the impedance of the oxide scale in LBE.

The impedance behavior of pre-oxidized iron in liquid lead-bismuth eutectic (LBE) at 200 °C is studied using electrochemical impedance spectroscopy. The structures and resistance of oxide grown on iron oxidized in air at different temperatures and durations are compared. The results show that the resistance of the oxide film increases with increasing oxidizing temperature, due to the formation of a thicker scale and fewer defects. At the same temperature (600 °C), increasing the oxidation time can also reduce the defect concentration in the oxide film and improve the impedance of the oxide scale in LBE.

• Fluid flow varied the pit morphology and concentration in the dynamic corrosion. • Shallow cracks with a surface open edge were induced in the corroded airfoil. • An allowable flaw size acted only as a stress concentrator. • Cracks in the leading-edge reduced the residual fatigue strength of the AA 2024-T3. • Load increment can increase the crack growth rate six times at the same degradation. Pitting corrosion creates preferential sites for cracks formation by the exfoliation process, which grow due to the continuous action of flight loads, even those of constant amplitude (CA). Whether the find-fix protocol must repair all defects, some may go unnoticed due to their sizes or locations in the aircraft. For this reason, it is necessary to study the fatigue behavior of airfoils with defects (cracks), analyzing their growth rates and the affectation on residual strength. This research work studied experimental and numerically fatigue performance of an airfoil with initial defects caused by dynamic corrosion. Intentionally, single-edge cracks (SECs) formation was induced in three wing skin regions: leading and trailing edges and central zone. The pre-corroded airfoil was subjected to alternate drag and lift forces to assess the crack growth and take validation data as deflection and the load level. The low stress intensity factor (SIF) estimated by means of a 3D finite element (FE) numerical model indicated that cracks did not propagate. Even though the stress level in the crack tip remained under the fatigue limit, giving rise to infinity life, the degraded material residual strength was considerably reduced. Also, the estimations obtained from an FE 1D model considering the damage factor and the mechanical properties loss in the crack region corroborated the infinity life behavior. Numerical and experimental results could determine an allowable flaw size under CA load conditions. However, the load variation play an important role increasing crack growth rate up to six times. [ABSTRACT FROM AUTHOR]