Zhenhai Xu

Deformation Behavior of Zr-Based Metallic Glass and Microforming of Microgears

The deformation behavior of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (Vit1) in the supercooled liquid region was investigated. The stress-strain relations for Vit1 at the different specimen sizes were established in a uniaxial compression test using the microforming system. Furthermore, the effects of forming time, temperature and punch velocity on the flow stress of the specimen with a typical size of Φ1×1.5 mm were analyzed. The results indicate that Vit1 has excellent superplastic microformability at minimum forming time, higher temperature and lower punch velocity. Based on the research, Vit1 microgears with reference diameter of Φ1 mm and modulus of 0.1 mm were manufactured using the closed die forging. Optimum processing parameters were obtained. In order to evaluate the quality of Vit1 microgears, scanning electron microscope, atomic force microscope and nanoindentation tests were applied. It is found that the parts with good qualities can be formed successfully in the supercooled liquid region.

Advancement in additive manufacturing & numerical modelling considerations of direct energy deposition process

The development speed and application range of the additive manufacturing (AM) processes, such as selective laser melting (SLM), laser metal deposition (LMD) or laser-engineering net shaping (LENS), are ever-increasing in modern advanced manufacturing field for rapid manufacturing, tooling repair or surface enhancement of the critical metal components. LMD is based on a kind of directed energy deposition (DED) technology which ejects a strand of metal powders into a moving molten pool caused by energy-intensive laser to finally generate the solid tracks on the workpiece surface. Accurate numerical modelling of LMD process is considered to be a big challenge due to the involvement of multiple phase changes and accompanied mass and heat flows. This paper overviewed the existing advancement of additive manufacturing, especially its sub-category relating to the DED. LMD process is analyzed in detail and subsequently broken down to facilitate the simulation of each physical stage involved in the whole process, including powder transportation and dynamics, micro-mechanical modelling, formation of deposited track and residual stress on the substrate. The proposed modelling considerations and a specific CFD model of powder feeding will assist in accurately simulating the DED process; it is particularly useful in the field of aerospace manufacturing which normally has demanding requirement on its products.