Tailoring the grain boundary network is desired to improve grain boundary-dependent phenomena such as intergranular corrosion. An important grain boundary network descriptor in heavily twinned microstructures is the twin-related domain, a cluster of twinrelated grains. We indicate the advantages of using twin-related domains and subsequent statistics to provide new insight into how a grain boundary networks respond to intergranular corrosion in a heavily twinned grain boundary engineered 316L stainless steel. The results highlight that intergranular corrosion is typically arrested inside twin-related domains at coherent twins or low-angle grain boundaries. Isolated scenarios exist, however, where intergranular corrosion propagation persists in the grain boundary network through higher-order twin-related boundaries.
Microstructural changes due to displacement damage and helium desorption are two phenomena that occur in tungsten plasma facing materials in fusion reactors. Nanocrystalline metals are being investigated as radiation tolerant materials that can mitigate these microstructural changes and better trap helium along their grain boundaries. Here, we investigate the performance of three tungsten grades (nanocrystalline, ultrafine and ITER grade tungsten), exposed to a high fluence of 4 keV helium at both RT and 773 K, during a thermal desorption spectroscopy (TDS) experiment. An investigation of the microstructure in pre-and post-TDS sample sets was performed. The amount of desorbed helium was shown to be highest in the ITER grade tungsten and lowest in the nanocrystalline tungsten. Correlating the desorption spectra and the microstructure (grain boundaries decorated with nanopores and crack formation) and comparing with previous literature on coarse grained tungsten samples at similar irradiation and TDS conditions, revealed the importance of grain boundaries in trapping helium and limiting helium desorption up to a high temperature of 1350 K in agreement with transmission electron microscopy studies on helium irradiated tungsten which showed preferential and large facetted bubble formation along the grain boundaries in the nanocrystalline tungsten grade.
This research investigates the effect of texture and grain boundary character on the corrosion response of Zircaloy-4 (Zry-4) using an in situ environmental cell in a transmission electron microscope (TEM). The corrosion response was studied in an oxygen rich environment at elevated temperatures, and monitored in real time using TEM bright field imaging and diffraction to observe the transition of Zry-4 from base metal to oxide.Zircaloy-4 is a commonly used material for nuclear fuel rod cladding, due to its low neutron cross section and good corrosion properties [1]. However, corrosion is still a limiting factor in fuel rod lifespan, which limits the burn up which can be achieved. As attempts are made to increase fuel burn up to reduce waste, more aggressive environments are being used, which results in more severe corrosion problems. In addition, Zirconium alloys are under consideration for some proposed Generation IV reactors, which also place high demands on these materials due to extreme conditions [2,3]. The corrosion response of Zry-4 has been well characterized via ex-situ experiments that simulate the environment found in light water reactors [3][4][5]. Much work has been done on autoclave-corroded samples, and the final oxide structure is well understood. However, almost all experimentation has been done after long periods of corrosion, and the initial steps of corrosion are not well understood. In order to design these alloys to be more corrosion resistant, the first steps of corrosion need to be observed, so that the effects of grain boundaries and other microstructural features can be determined.
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