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

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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.