Hydrogen embrittlement (HE) is a serious material deterioration phenomenon that can cause sudden failure of metallic parts subjected to static or cyclic loads, leading to service interruptions and financial losses. HE can result in delayed fracture of components with vulnerable microstructure that contain exceedingly small concentrations of diffusive hydrogen. Sources of hydrogen ingress into material can be either external, such as a corrosion reaction, or internal, such as electroplating process. Cd-plated 4340 high strength steel components, used for manufacturing aircraft landing gears, are particularly prone to HE. Such parts are heattreated during a process called baking to encourage the egress of electroplating-induced hydrogen. However, there are concerns about the efficiency of baking as well as the effect of inevitable delays between electroplating and baking on the risk of HE. It is therefore beneficial to develop a non-destructive evaluation (NDE) method to ensure that dissolved hydrogen level is dropped below a certain concentration threshold in Cd-plated parts. In other words, such NDE method shall ideally be able to quantitatively evaluate the susceptibility of Cd-plated steel parts to HE. However, there are numerous challenges which hinder achieving this goal. Firstly, such small hydrogen concentrations are below the sensitivity level of many conventional NDE techniques. Moreover, research on NDE of HE has so far has been focused on parts subjected to direct hydrogen charging that involve high hydrogen concentrations, the results of which may not be applicable to case of Cd-plated steel. As an initial but necessary step in research to address the problem, the present study assesses the feasibility of candidate NDE methods that were deemed sensitive to hydrogen-induced variations in near-surface material properties of Cd-plated steel samples. The aim was to distinguish between samples with low and high HE susceptibilities. For this purpose, non-destructive measurements based on surface acoustic waves (SAW) as well as eddy current testing (ECT) were performed on several samples manufactured in not-baked, late-baked and immediately-baked conditions. Destructive tests as well as microscopy techniques were performed in parallel to characterize test samples. Computer simulations of NDE results were also performed to evaluate the hydrogen-induced changes in relevant material properties.
| Date | 8 Jun 2021 |
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| Original language | American English |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Martin Viens (Supervisor) |
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Shahmiri, H. (Author),
Viens (Supervisor),
8 Jun 2021Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering