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The oxidation behaviors of molten WE43 (Mg-4.32Y-2.83Nd-0.41Zr, wt%) in resin-sand mold atmosphere were systematically investigated. X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy analyses were employed to identify the phase compositions and microstructures of surface oxide scale. The initial oxide scale characterized by a three-layer structure mainly consisted of MgO, Y2O3, and ZrO2 and then transformed to Y2O3 layers covered by porous MgO after holding at high temperatures. CALPHAD method was used to analyze the oxidation process, and the calculated phase diagrams agreed well with the experimental results. A selective oxidation model was established based on thermodynamic and kinetic analysis to describe the structure transformation of oxide scale in detail. The initial oxidation was controlled by inward diffusion of oxygen due to the protection of surface Y2O3. However, the oxide scale was not protective after long-term oxidation or at temperatures higher than 1073 K due to the oxide fracture, which can be attributed to the increase in stress caused by inner Y2O3 layer growth. Based on experimental results, the oxide growth stress parameter C was estimated to be 0.0013 and 0.0026 for 1023 and 973 K, respectively. This work reveals the underlying oxide growth and fracture mechanisms of molten Mg-Y alloy in mold, and provides guidance for preventing the ignition of magnesium alloys during casting processes. [ABSTRACT FROM AUTHOR]

Ceramic capacitors are receiving increasing interest because of their applications in pulsed-power devices. The perovskite oxide Bi0.5Na0.5TiO3 (BNT)-based ferroelectric ceramics are regarded as prospective lead-free candidate for dielectric capacitors because of the high polarization and outstanding relaxor behaviour. Herein, the relaxor ferroelectric (0.7−x)Bi0.5Na0.5TiO3–0.3SrTiO3–xCa0.7Sm0.2TiO3 ceramics synthesized through solid-state route and exhibited pseudocubic perovskite structure and strong relaxor behaviour. With increasing Ca0.7Sm0.2TiO3 content, the moderate permittivity and reduced grain size contributed to the monotonically increased electric breakdown strength. Among prepared samples, the x = 0.2 ceramic displayed slimmer polarization-electric field curves with a remarkable recoverable energy density (~6.8 J/cm3) and a satisfied efficiency (~82.2%) under external electric field of 450 kV/cm. Moreover, the x = 0.2 ceramic also exhibited a superb thermal reliability of energy storage properties (3.9–4.5 J/cm3 with variation of 13.3% in 25–160 °C) resulting from the diffuse phase transition. The above results make the x = 0.2 ceramics becoming promising candidates for pulsed-power devices. [ABSTRACT FROM AUTHOR]