Many manufacturing processes (including laser hardening, laser welding, laser texturing, and laser polishing) use surface heating and melting to create metal products. They are normally used to achieve one outcome: hardening or smoothing. The ability to simultaneously achieve both outcomes through pulsed laser polishing will save time and money, and benefit manufacturers of medical devices, optical instruments, automobile plastic components, aerospace parts, bearings, cutting tools, and many other products. This award supports fundamental research to enable this ability. Results of this research will be valuable to a wide range of manufacturing processes that utilize focused energy beams to locally heat and/or re-melt metal surfaces, e.g., laser texturing, laser welding, electron beam welding, laser cladding, laser peening, and laser heat treating. New knowledge will be widely disseminated through publications and integrated into undergraduate and graduate courses, thereby helping to train the future workforce.
The research objectives are to test two hypotheses. The first hypothesis is that alloying or adding nanoparticles to a metal will substantially increase its viscosity and surface tension when it is in a liquid state, resulting in a smoother surface after laser re-melting as compared to metals with lower viscosity and surface tension. This hypothesis will be tested in two steps. First, the viscosity and surface tension of liquid-state aluminum alloys whose surfaces are modified with nanoparticles or boron will be determined to see if there is a significant difference compared to unaltered surfaces. Dynamic nanoindentation with long hold/creep durations and nano-scale pull-off (adhesion) experiments will be used to determine the viscosity and surface tension, respectively. Secondly, the measured viscosity and surface tension of alloyed and nanoparticle embedded surfaces will be measured with a white light interferometer and focus-variation-based optical metrology system to confirm that changes in viscosity and surface tension are the cause of any observed changes to the surface texture. A second hypothesis is that adding boron or nanoparticles to the surface of a metal alloy will have significant effects on the microstructure kinetics during laser re-melting, resulting in harder surfaces as compared to metals without surface modification. This hypothesis will be tested by using electron microscopy and x-ray diffraction to observe the effects of laser re-melting on the microstructures of aluminum and steel alloys whose surfaces are modified. Nanoindentation tests will also be conducted on these laser re-melted samples in order to measure their hardness.
