Ultra-short pulse laser machining has been applied to the polishing of polycrystalline diamond (PCD) wafers in order to generate a smooth surface finish and reduce mechanical polishing time. Past studies were first carried out with a 5W laser highlighting the difference in ablation rates between PCD grades and the possible graphitization of diamond on the surface of micrometric PCD grades over a fluence threshold. Some upscaling work was undertaken at 80W with a 3-pulse burst reducing the Sa of a micrometric PCD grade lapped surface by 50% with a volume removal rate double that of the conventional mechanical polishing technique. From these previous base investigations, an ultra-short pulse laser delivering an average power of 1kW at 500fs via state-of-the-art thin disk multi-pass amplification is implemented here to achieve a higher ablation rate for high throughput processing. This is the first time that such an average power is applied on polycrystalline diamond in the ultra-short pulse regime. A burst mode is also implemented which is demonstrated to reduce the Sa by 10% and 55% on fine and coarse grade surfaces respectively compared to single pulse processing. From 80W to 1kW, the ablation rate is increased by a factor of 70 on micrometric PCD grades while the Sa of the initial lapped surface is reduced by 14% without any graphitization of the diamond structure. However, no improvement of the Sa is performed on the initial surface of coarser grades due to the formation of cavities (~5μm wide) potentially caused by the spallation of diamond grains.
Properties of diamond are extreme. Since the first successful synthesis of diamond in 1955, the use of synthetic diamond has widely spread into diverse industries (e.g. manufacturing, electronics and optics). However, being the hardest material known, the manufacture of diamond material into an engineered tool is extremely challenging. The polishing process remains a traditional mechanical method existing for over hundreds of years. The development of alternative ways of polishing diamond is an active subject of research and has recently been investigated in topics such as chemically assisted mechanical polishing or ion beam polishing. Laser polishing is another alternative and a state-of-theart laser polishing method is presented in this paper. A high-power femtosecond laser ablation process is developed to achieve a high throughput polishing process of polycrystalline diamond composite (PCD) wafers. Laser ablation trials are carried out with a femtosecond laser delivering over 80W average power on three different PCD grades synthesized by high-pressure/high-temperature. The role of the fluence is highlighted and the effect of the burst mode on PCD is demonstrated for the first time to the best of our knowledge. Eventually, the roughness of the initial surface on fine grain diamond material is reduced by two while the ablation rate is twice higher than the removal rate achieved by mechanical polishing.
Diamond exhibits incredible chemical and mechanical properties. Utilization of diamond for industrial applications has universally spread thanks to the discovery of its industrial synthesis and the enhancement of its properties by its formation under a polycrystalline form, named polycrystalline diamond composite (PCD). For industrial production PCD bulk material has to pass through several complex processes from leaving the belt press down to be polished as a wafer with a mirror-finished surface. Especially the polishing process is an extremely laborious method originally discovered to polish diamond gemstones hundred years ago. Laser ablation has repeatedly been proven to be a cost efficient process for industrial purposes. Elaboration of new ablation processes for PCD manufacturing is increasing supported by the continuous improvement of ultra-short lasers and their high performances. The ambition of this project is to develop an alternative polishing process of PCD wafers by ultra-short laser ablation achieving better performances than traditional mechanical polishing. This paper presents a relationship between material related properties of various PCD grades and performance of ultra-short laser ablation process at low laser average power. Specifically, this paper demonstrates the high impact of the pulse duration on the ablation rate, the dependence of the optimal fluence for highest ablation rate on the PCD composition and the effect of fluence on diamond graphitization through Raman spectroscopy analysis.
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