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This study addresses the critical need for a constitutive model to analyze the cyclic plasticity of additively manufactured 316L stainless steel. The anisotropic behavior at both room temperature and 300 °C is investigated experimentally based on cyclic hysteresis loops performed in different orientations with respect to the build direction. A comprehensive constitutive model is proposed, that integrates the Armstrong-Frederick nonlinear kinematic hardening, Voce nonlinear isotropic hardening and Hill's anisotropic yield criterion within a 3D return mapping algorithm. The model was calibrated to specimens in the 0° and 90° orientations and validated with specimens in the 45° orientation. A single set of hardening parameters successfully represented the elastoplastic response for all orientations at room temperature. The algorithm effectively captured the full cyclic hysteresis loops, including historical effects observed in experimental tests. A consistent trend of reduced hardening was observed at elevated temperature, while the 45° specimen orientation consistently exhibited the highest degree of strain hardening. The applicability of the model was demonstrated by computing energy dissipation for stabilized hysteresis loops, which was combined with fatigue tests to propose an energy-based fatigue life prediction model., QC 20240514

In light water reactors corrosion-induced material degradation is a critical issue not only for material integrity but also for plant radiation field build-up. In BWRs nickel-base alloys, such as Alloy 600, Alloy 82 and Alloy 182, are applied in various parts of reactor components including welds. However, their corrosion mechanisms are not very well understood. Although the complex compositions of different nickel-base alloys generally prohibit us to single out some specific alloy constituent having a major impact on alloy corrosion rate, a higher chromium content is often thought to be beneficial to forming a more protective oxide film against corrosion attack. In this paper we report a corrosion kinetics study on high chromium nickel-base alloy welding consumables, Alloy 52M and Alloy 152, under simulated BWR normal water chemistry conditions and high flow velocity for up to nine weeks exposure. The corrosion rates are derived from measurements of weight losses of test coupons, oxide thicknesses with infrared ellipsometry, and microstructures of oxide films with electron microscopy. The obtained corrosion rates are then compared to that for Alloy 182, Alloy 82 and Alloy 600. The results show that the corrosion rate for Alloy 52M is similar to those for Alloy 182, whereas the rate for Alloy 152 is reduced to less than half. These observations indicate that the corrosion kinetics for nickel-base alloys is complex and alloy chromium content alone is not a dominant factor in influencing alloy corrosion rate.

This work contributes to characterization of the oxide films formed on nickel-base alloys (Alloy X-750, Alloy 82 and Alloy 182) under simulated BWR water environments at ∼10 or 18 m/s with or without iron injection. HR SEM/TEM and FIB techniques were applied. The oxide thicknesses on different alloys were substantially different, ranging from 50 nm to 8 μm. For Alloy X-750 and Alloy 182 exposed without iron injection, similar oxide phase compositions consisting of sub-micron Fe2O3 and NiFe 2O4 grains as well as NiO were formed but with substantially different microstructures. For the corroded Alloy X-750 there was an additional dense layer of possibly Ni1.5Cr0.5O 3 in between the NiFe2O4 and NiO layers. On Alloy 82 which contained a relatively low Fe-content only a thin but dense film of Cr1.3Fe0.7O3 was seen. With iron injection the oxide films formed on Alloy 82 were similar to that on the Alloy 182 without iron injection, suggesting that iron injection may play a similar role as if the alloy had an elevated iron content. The implication of the observations for material corrosion behavior in BWRs is elaborated., QC 20140908