In-situ TEM study of the Corrosion Behavior of Zry-4

Abstract

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.

Theory and New Applications ofEx SituLift Out

“…Each specimen lift out and manipulation process took only 2–5 min to perform. Once the specimen is manipulated to the MEMS carrier, it can be put back into the FIB-SEM where electron beam assisted deposition can be used to secure the specimen to the carrier to prevent drift during heating (Harlow et al, 2014).

Figure 6 Electron transparent ex situ lift out specimens manipulated to ( a ) Protochips, Inc. MEMS carrier device and ( b ) DENSsolutions MEMS carrier device.

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“…Carrier devices prepared via MEMS technology allow for in situ S/TEM heating (or electrical) characterization of materials (Allard et al, 2009;Young et al, 2010). Conversely, EXLO of site specific and electron transparent FIB prepared specimens lends itself nicely for the precise placement of specimens onto these delicate MEMS devices (Bassim et al, 2014;Harlow et al, 2014) and examples will be described below. Lift out for positioning on MEMS devices performed inside the FIB (e.g., in situ lift out (INLO)) requires multiple manipulation and FIB milling steps to ensure that a suitable region of interest is electron transparent without FIB imaging or milling the MEMS support device (Duchamp et al, 2014).…”

“…Each specimen lift out and manipulation process took only 2-5 min to perform. Once the specimen is manipulated to the MEMS carrier, it can be put back into the FIB-SEM where electron beam assisted deposition can be used to secure the specimen to the carrier to prevent drift during heating (Harlow et al, 2014).…”

“…As FIB imaging and ion beam deposition methods are necessary during INLO, the specimen is always lifted out “thick” and then final FIB polished after manipulation to a grid carrier. Conversely, EXLO of site specific and electron transparent FIB prepared specimens lends itself nicely for the precise placement of specimens onto these delicate MEMS devices (Bassim et al, 2014; Harlow et al, 2014) and examples will be described below.…”

Convenient Preparation of High-Quality Specimens for Annealing Experiments in the Transmission Electron Microscope

“…Focused ion beam (FIB) milling is a well-established technique for preparing specimens for TEM (Giannuzzi et al, 1997; Langford & Petford-Long, 2000; Kempshall et al, 2002; Rogers et al, 2005; Jeangros et al, 2010; Harlow et al, 2014). The main advantages of FIB milling over conventional TEM specimen preparation include fast and reproducible preparation and site specificity.…”