Papers by Author: Qi Wu

Abstract: The mechanism of ultrashort pulsed laser ablation of polycrystalline diamond (PCD) is investigated using molecular dynamics simulation. The simulation model provides a detailed atomic-level description of the laser energy deposition to PCD specimens and is verified by an experiment using 300 fs laser irradiation of a PCD sample. It is found that grain boundaries play an important role in the laser ablation. Melting starts from the grain boundaries since the atoms in these regions have higher potential energy and are melted more easily than the perfect diamond. Non-homogeneous melting then takes place at these places, and the inner crystal grains melt more easily in liquid surroundings presented by the melting grain boundaries. Moreover, the interplay of the two processes, photomechanical spallation and evaporation, are found to account for material removal in ultrashort pulsed laser ablation of PCD.

Abstract: A femtosecond pulsed Nd:YAG laser was used to micromachine polycrystalline diamonds (PCD) and study the ablated microstructure characteristics under different irradiation parameters. With high laser intensity and low traverse speed, a micro cone with very smooth surface and clear edge can be obtained. There was almost no recast layer around the cone and no phase transition on the ablated surfaces was found. By contrast, the use of low laser intensity and high traverse speed could ablate only the grain boundaries without any damage to the diamond grits. These results suggest a need for further research in femtosecond laser micromachining of PCD for potential applications in fabricating new types of micro grinding wheels or diamond pencils.

Abstract: An experimental study of the pulsed laser milling process for a sintered polycrystalline diamond is presented. The characteristics and quality of the cavities machined with a Yd laser under different pulse energies, pulse overlaps, scan overlaps and numbers of passes are discussed, together with the effects of these parameters on the cavity profile, depth of cut and surface roughness. A statistical analysis is also presented to study the relationship between the process parameters and surface roughness. It shows that the optimum pulse overlap and pulse energy may be used to achieve good surface finish, whereas scan overlap and number of passes can be selected to improve the depth of cut without much effect on the surface finish.

Abstract: Laser polishing is a surface finishing technology for polycrystalline diamond (PCD) tools by removing uneven diamond particles from the diamond film through graphitization, melting and sublimation. While various types of lasers are used for the polishing of PCD tools, pulsed excimer and Nd: YAG lasers are among the most commonly used ones. The current development in laser polishing of PCD tools is reviewed. The reported experimental and modelling studies to improve the process performance are discussed. It reveals that there is a severe dearth of understanding of the process and the associated models for the efficient and effective use of the technology. The direction of future research in laser polishing is finally discussed.