Ultrasonic Vibration Assisted Surface Texturing of Bulk Metallic Glasses for Enhancing Tribological Performance

我的长期研究目标是提高对精密制造过程中的力学和材料响应的理解，以提高部件表面质量，包括形貌和微观结构特性。在未来五年内，我的研究将集中在超声振动辅助下大块金属玻璃（BMG）表面织构的基本机制。BMG是一类新型的非晶态金属合金。BMG已越来越多地用于各种工业应用中，例如轴承部件。表面纹理是一种产生重复表面图案的技术，这些图案充当润滑剂储存器以有益于轴承系统的摩擦学性能。现有的表面织构化工艺，如化学蚀刻和激光织构化，是不适合的BMG，因为它们的不利的环境影响和工艺诱导的微观结构修改。机械加工能够在保持原始材料相的同时获得纹理表面。机械毛化的主要挑战是由冲击力引起的工具尖端断裂和表面损伤。为了克服这一障碍，提出了一种新的毛化技术，使用高进给铣削与超声振动辅助（VA）。VA修改了刀尖轨迹，并大大降低了切屑负荷。这可能是由于VA促进了非均匀变形向均匀变形的转变，从而减少了表面损伤。在理解表面纹理化过程中的工艺参数如何定量影响纹理几何形状和表面质量方面存在知识差距。**提出了以下研究计划：（1）发展一种新的超声振动微压痕技术，用于研究大应变、高应变率、变温和重复载荷下BMG的本构行为：（2）研究织构化工艺参数对BMG非均匀变形的影响;（3）将预测作为具有2D振动辅助的工具尖端振动结果的表面形貌。**预计这项研究将对工业产生广泛的影响。生物相容性BMG已被开发为新的植入材料。与传统使用的钛相比，BMG的优点是其低弹性模量，几乎与骨骼的弹性模量相匹配，因此减少了对骨骼的损伤。在植入物上生成表面纹理，以增强骨-植入物结合。具有表面纹理的BMG也已被用作用于制造结构化微光学器件的模具。本研究将提供指导，在确定工艺参数，以提高纹理质量没有试错过程。因此，将实现具有高几何精度和表面质量的具有成本效益的表面纹理化技术。

My long-term research goal is to advance the understanding of the mechanics and the material response in precision manufacturing processes, in order to enhance the component surface quality including topography and microstructural property. In the next five years, my research will focus on the fundamental mechanisms in surface texturing of bulk metallic glasses (BMGs) with ultrasonic vibration assistance.******BMGs are a new category of metal alloys with non-crystalline structure. BMGs have been increasingly used in various industrial applications, e.g. the bearing components. Surface texturing is a technique to generate repeated surface patterns which act as lubricant reservoirs to benefit the tribological performance of the bearing system. Existing surface texturing processes such as chemical etching and laser texturing are not suitable for BMGs because of their adverse environmental impact and process induced microstructure modification. Mechanical machining is able to achieve textured surface while keeping the original material phase. The main challenges of mechanical texturing are tool tip fracture and surface damages caused by the impact force. To overcome this barrier, a new texturing technique using high-feed milling with ultrasonic vibration assistance (VA) is proposed. VA modifies the tool tip trajectory and extensively reduces the chip load. It is hypothesized that the VA enhances the transition of BMG deformation from inhomogeneous to homogeneous mode, therefore reducing the surface damage. There is knowledge gap in understanding how the process parameters in surface texturing quantitatively influence the texture geometry and the surface quality.******The following research plan is proposed: (1) a new micro-indentation technique with ultrasonic vibration feature will be developed to identify the constitutive behavior of BMG under large strain, high strain rate, varying temperature and repeated load; (2) the effect of texturing process parameters on the inhomogeneous-homogeneous deformations of BMG will be determined; (3) the surface topography as a result of the tool tip vibrations with 2D vibration assistance will be predicted.******This proposed research is expected to bring broad impacts to industry. Biocompatible BMGs have been developed as new implant materials. The advantage of BMGs compared to conventionally used titanium is their low elastic moduli which nearly match that of bones, therefore reducing the damage to the bones. Surface texture is generated on the implant to enhance the bone-implant bonding. BMGs with surface texture also have been used as molds for the fabrication of structured micro optics. This research will provide guidance in determining process parameters to improve the texture quality without trial-and-error processes. As a result, a cost-effective surface texturing technique with high geometric accuracy and surface quality will be achieved.