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This dissertation includes a thorough investigation into the effects of high energy multilayer laser peening (LP) and shot peening (SP) of Ni-Cr-Mo high-strength low-alloy (HSLA) steels including 4340 and 300M and the Ni-Cr alloy, alloy 625 (Inconel 625). In this work the effectiveness of these two different surface engineering techniques has been evaluated to determine how the mechanical properties and microstructures of these alloys evolve following deformation and how these evolutions in material properties enhance these alloys’ resistance to wear, corrosion, and exposure to high temperature. Advanced characterization techniques have been used to draw correlations between local mechanical properties and microstructural alterations resulting from surface engineering of these alloys to understand their structure-property relationships.
The first two studies compare the effects of high energy multi-layer LP and full coverage SP on the mechanical properties and microstructural evolution of two Ni-Cr-Mo HSLA steels including 4340 and 300M, while the third and fourth studies investigate the effects of these techniques on alloy 625. In the first study the local mechanical and microstructural properties of 4340 steel with a pearlitic microstructure were investigated following surface engineering. In the second study these techniques were used to pretreat 300M prior to high-velocity oxygen fuel (HVOF) deposition of a WC-Co coating to investigate the impact of these techniques on enhancing the corrosion fatigue life of WC-Co coated 300M. The third study exploits the age-hardenability of alloy 625 by employing multi-layer high energy LP and SP prior to aging to locally accelerate the nucleation and precipitation of γ՛՛ and δ intermetallic phases. The final study includes an analysis on the effects of high energy multi-layer LP and SP on the mechanical, microstructural, and tribological properties of centrifugally-cast alloy 625.
In summary, this dissertation examines three different engineering alloys that are used to manufacture components used in critical applications to understand how these alloys’ mechanical properties and microstructures evolve following surface engineering. This work highlights these alloys’ susceptibility to plastic deformation based on their underlying microstructures and demonstrates how these surface engineering techniques can be employed with other manufacturing or processing techniques to further enhance their capabilities.