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 Title: Microstructure and mechanical properties of laser shocked iron-based alloys Author(s): Chu, Jinn P. Doctoral Committee Chair(s): Rigsbee, J. Michael Department / Program: Materials Science and Engineering Discipline: Materials Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Engineering, Metallurgy Engineering, Materials Science Abstract: The effects of laser shock processing (LSP) on the microstructure and mechanical properties of the low carbon (0.04 wt.%C) and Hadfield manganese (1%C and 14%Mn) steels have been studied. LSP was performed with a 1.054 $\mu$m wavelength Nd:phosphate laser operating in a pulse mode (600 ps pulse length and up to 200 J energy) with power densities above 10$\sp{11}$ W/cm$\sp2$. Shock waves were generated by volume expansion of the plasma formed when the material was laser irradiated. Maximum shock wave intensities were obtained using an energy-absorbing black paint coating without a plasma-confining overlay. Maximum modification of the material surface properties and favorable compressive residual stresses were achieved when LSP-induced deformation occurred without melting.Mechanical properties of materials such as surface hardness were greatly improved through modifying the microstructure by LSP. High density arrays of dislocations ($>$10$\sp{11}$/cm$\sp2$) were generated in low carbon steel by high strain-rate deformation of LSP, resulting in surface hardness increases of 30 to 80%. In austenitic Hadfield steel, LSP caused extensive formation of $\epsilon$-hcp martensite (35 vol.%), producing increases of 50 to 130% in surface hardness. The LSP strengthening effect in Hadfield steel was attributed to the combined effects of the partial dislocation/stacking fault arrays and the grain refinement due to presence of the $\epsilon$-hcp martensite. Surface and near surface compressive residual stresses due to plastic deformation by LSP were measured in both steels. Comparisons of LSP microstructure and properties were made with the lower strain rate processes of shot peening and cold rolling for both steels. Issue Date: 1992 Type: Text Language: English URI: http://hdl.handle.net/2142/21825 Rights Information: Copyright 1992 Chu, Jinn P. Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9236428 OCLC Identifier: (UMI)AAI9236428
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