Evaluating the Effect of Laser and Shot Peening on Hydrogen Diffusivity and Trapping and Corrosion Susceptibility in High Strength Steel

Abstract

Electronic Thesis or DissertationThis thesis will present work on the effect of laser peening and shot peening on hydrogen diffusivity and trapping in 4340 high strength steel, along with corrosion behavior. Surface engineering, such as laser peening and shot peening, imparts plastic deformation resulting in compressive residual stresses and increased dislocation densities. This has been shown to dramatically increase fatigue life in various materials and applications. However, due to the sensitivity of high strength steels to hydrogen embrittlement, it is unknown how the increased hardness and dislocation density caused by laser peening will affect processes related to hydrogen-influenced cracking. In this work, electrochemical procedures were used to assess these structure-property relationships. Hydrogen permeation testing was conducted per ASTM G148-97, which allowed for calculating the effective hydrogen diffusivity of laser peened, shot peened, and unpeened 4340. Hydrogen trapping was also evaluated through electrochemical potentiostatic hydrogen charging and discharging. A roughly order-of-magnitude decrease in diffusivity was found within the laser peened region due to the increase in trap density