Pulsed ion beam treatment of metals for improved surface properties

Summary form only given. This work builds on previously reported studies using an intense pulsed ion beam to achieve a rapid melt and resolidification (RMR) of a surface metallic layer. Alloys and bi-metal combinations were treated on the RHEPP-1 facility at Sandia National Laboratories (0.5 MV, 0.5 /spl mu/s at sample location, <10 J/cm/sup 2/). The ions are produced by an epoxy-filled groove flashover source, yielding a mixed species beam of protons and carbon (ranges 1 /spl mu/m and 5 /spl mu/m respectively) from a magnetically insulated ion diode. Numerical modeling of thermal histories neglecting ablation have yielded predictions consistent with diagnostic measurements of treated samples. The measurements included scanning electron microscopy (SEM), Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), and electrochemical corrosion tests. Treatment of Al-, Fe-, and Ti-based alloys with multiple beam shots indicates that the extent and nature of beam-induced modification depends on the particular alloy, and on the total number of RMR cycles. Microhardness measurements of a treated and sectioned SS-304 sample show enhancements over bulk values of as much as 50%, and extending over 100 /spl mu/m below the surface. Optical microscopy shows shear bending extending at least 80 /spl mu/m below the surface. In the absence of ablation, we attribute this deep-lying modification to a mechanical stress wave generated by the RMR cycle. In treatment of bi-metal combinations (ion beam mixing), we have investigated overcoats on Al-, Fe, and Ti-based alloys, where the overcoat layer is applied to the substrate by conventional means such as sputter deposition.