Combining Laser Melting, Alloying, and Nanoparticles to Make Harder and Smoother Surfaces on Metal Alloys

许多制造工艺（包括激光硬化、激光焊接、激光纹理化和激光抛光）使用表面加热和熔化来制造金属产品。它们通常用于实现一个结果：硬化或平滑。通过脉冲激光抛光同时实现这两种结果的能力将节省时间和金钱，并使医疗器械，光学仪器，汽车塑料部件，航空航天部件，轴承，切割工具和许多其他产品的制造商受益。该奖项支持基础研究，使这种能力。这项研究的结果将对利用聚焦能量束局部加热和/或再熔化金属表面的各种制造工艺有价值，例如，激光纹理化、激光焊接、电子束焊接、激光熔覆、激光喷丸和激光热处理。新知识将通过出版物广泛传播，并纳入本科和研究生课程，从而帮助培训未来的劳动力。第一个假设是，当金属处于液态时，将纳米颗粒合金化或添加到金属中将大大增加其粘度和表面张力，从而与具有较低粘度和表面张力的金属相比，在激光重熔后产生更光滑的表面。这一假设将分两步进行检验。首先，将测定其表面用纳米颗粒或硼改性的液态铝合金的粘度和表面张力，以查看与未改变的表面相比是否存在显著差异。将使用具有长保持/蠕变持续时间的动态纳米压痕和纳米级拉脱（粘附）实验来分别确定粘度和表面张力。其次，将用白色光干涉仪和基于焦点变化的光学计量系统测量合金化和纳米颗粒嵌入表面的测量粘度和表面张力，以确认粘度和表面张力的变化是任何观察到的表面纹理变化的原因。第二个假设是，在激光重熔期间，向金属合金的表面添加硼或纳米颗粒将对微观结构动力学产生显著影响，从而导致与没有表面改性的金属相比更硬的表面。 这一假设将通过使用电子显微镜和X射线衍射观察激光重熔对铝和钢合金的表面改性的微观结构的影响进行测试。还将对这些激光重熔样品进行纳米压痕测试，以测量其硬度。

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.