scholarly journals Investigation of the Use of Laser Shock Peening for Enhancing Fatigue and Stress Corrosion Cracking Resistance of Nuclear Energy Materials

2017 ◽  
Author(s):  
Vijay K. Vasudevan ◽  
◽  
John Jackson ◽  
Sebastien Teysseyre ◽  
Bogdan Alexandreanu ◽  
...  
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Energy ◽  
Corrosion Cracking ◽  
Laser Shock Peening ◽  
Laser Shock ◽  
Energy Materials ◽  
Cracking Resistance ◽  
Shock Peening

Laser Shock Peening for Suppression of Hydrogen-Induced Martensitic Transformation in Stress Corrosion Cracking

2017 ◽  
Vol 139 (8) ◽  
Author(s):  
Grant Brandal ◽  
Y. Lawrence Yao
Keyword(s):  
Stainless Steel ◽  
Martensitic Transformation ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Laser Shock Peening ◽  
Simple Explanation ◽  
Laser Shock ◽  
Hydrogen Atoms ◽  
Shock Peening

The combination of a susceptible material, tensile stress, and corrosive environment results in stress corrosion cracking (SCC). Laser shock peening (LSP) has previously been shown to prevent the occurrence of SCC on stainless steel. Compressive residual stresses from LSP are often attributed to the improvement, but this simple explanation does not explain the electrochemical nature of SCC by capturing the effects of microstructural changes from LSP processing and its interaction with the hydrogen atoms on the microscale. As the hydrogen concentration of the material increases, a phase transformation from austenite to martensite occurs. This transformation is a precursor to SCC failure, and its prevention would thus help explain the mitigation capabilities of LSP. In this paper, the role of LSP-induced dislocations counteracting the driving force of the martensitic transformation is explored. Stainless steel samples are LSP processed with a range of incident laser intensities and overlapping. Cathodic charging is then applied to accelerate the rate of hydrogen absorption. Using XRD, martensitic peaks are found after 24 h in samples that have not been LSP treated. But martensite formation does not occur after 24 h in LSP-treated samples. Transmission electron microscopy (TEM) analysis is also used for providing a description of how LSP provides mitigation against hydrogen enhanced localized plasticity (HELP), by causing tangling and prevention of dislocation movement. The formation of dislocation cells is attributed with further mitigation benefits. A finite element model predicting the dislocation density and cell formation is also developed to aid in the description.

Material Influence on Mitigation of Stress Corrosion Cracking Via Laser Shock Peening

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Grant Brandal ◽  
Y. Lawrence Yao
Keyword(s):  
Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
High Strength Steel ◽  
High Strength ◽  
Corrosion Cracking ◽  
Laser Shock Peening ◽  
304 Stainless Steel ◽  
Laser Shock ◽  
Shock Peening

Stress corrosion cracking is a phenomenon that can lead to sudden failure of metallic components. Here, we use laser shock peening (LSP) as a surface treatment for mitigation of stress corrosion cracking (SCC), and explore how the material differences of 304 stainless steel, 4140 high strength steel, and 260 brass affect their mitigation. Cathodic charging of the samples in 1 M sulfuric acid was performed to accelerate hydrogen uptake. Nontreated stainless steel samples underwent hardness increases of 28%, but LSP treated samples only increased in the range of 0–8%, indicative that LSP keeps hydrogen from permeating into the metal. Similarly for the high strength steel, LSP treating limited the hardness changes from hydrogen to less than 5%. Mechanical U-bends subjected to Mattsson's solution, NaCl, and MgCl2 environments are analyzed, to determine changes in fracture morphology. LSP treating increased the time to failure by 65% for the stainless steel, and by 40% for the high strength steel. LSP treating of the brass showed no improvement in U-bend tests. Surface chemical effects are addressed via Kelvin Probe Force Microscopy, and a finite element model comparing induced stresses is developed. Detection of any deformation induced martensite phases, which may be detrimental, is performed using X-ray diffraction. We find LSP to be beneficial for stainless and high strength steels but does not improve brass's SCC resistance. With our analysis methods, we provide a description accounting for differences between the materials, and subsequently highlight important processing considerations for implementation of the process.

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