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

我的长期研究目标是加深对精密制造过程中的力学和材料响应的理解，以提高零件的表面质量，包括表面形貌和微观结构性能。在接下来的五年里，我的研究重点将集中在超声振动辅助下大块金属玻璃表面毛化的基本机理上。大块金属玻璃是一类具有非晶态结构的新型金属合金。BMG已越来越多地应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，从而有利于轴承系统的摩擦学性能。现有的表面毛化工艺，如化学刻蚀和激光毛化，由于其对环境的不利影响和工艺引起的微结构改变，不适合用于BMG。机械加工能够在保持原始材料物相不变的情况下实现表面纹理。机械毛化的主要挑战是刀尖断裂和冲击力造成的表面损伤。为了克服这一障碍，提出了一种利用超声振动辅助(VA)的高进给铣削毛化新技术。Va修改了刀尖轨迹，并广泛降低了芯片负载。假设VA促进了BMG变形从非均匀模式向均匀模式的转变，从而减少了表面损伤。对于表面毛化工艺参数如何定量地影响织构几何形状和表面质量的认识还存在空白，提出了以下研究计划：(1)开发一种新的具有超声振动特征的微压痕技术，以识别大应变、高应变率、变温和重复载荷下的BMG的本构行为；(2)确定毛化工艺参数对BMG非均匀变形的影响；(3)对二维振动辅助下刀尖振动产生的表面形貌进行了预测。*本研究有望对工业产生广泛影响。生物相容性BMG作为一种新型的植入材料已经被开发出来。与传统使用的钛相比，BMG的优势在于其弹性系数较低，几乎与骨骼的弹性系数相匹配，因此减少了对骨骼的损伤。在种植体上产生表面纹理，以增强骨与种植体的结合。具有表面织构的BMG也被用作制造结构微光学的模具。这项研究将为确定工艺参数以提高织构质量提供指导，而不需要反复试验。因此，将获得具有高几何精度和表面质量的高性价比的表面纹理技术。

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.