Ablation threshold is an important concept in the study of femtosecond laser micro-and nano-machining.In this paper,the ablation experiments of three kinds of surface roughness 4H-Si C substrates irradiated by femtose...Ablation threshold is an important concept in the study of femtosecond laser micro-and nano-machining.In this paper,the ablation experiments of three kinds of surface roughness 4H-Si C substrates irradiated by femtosecond laser were carried out.The feature thresholds were systematically measured for three surface roughness Si C substrates and found in the modification and annealing regions ranging from coincidence(R_(a)=0.5 nm)to a clear demarcation(R_(a)=5.5 nm),eventually being difficult to identify the presence of the former(R_(a)=89 nm).Under multi-pulse laser irradiation,oriented ripple structures were generated in the annealing region,where deep subwavelength ripples(about 110 nm,Λ≈0.2λ)can be generated above substrates with surface roughness higher than 5.5 nm.We investigated the effect of surface roughness on the ablation morphology,ablation threshold,and periodic structures of femtosecond laser ablation of 4H-Si C substrates,while the ablation threshold was tended to decrease and stabilize with the increase of pulse number N≥500.展开更多
Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（ma...Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（mass fraction） alloy with low carbon-containing level by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）, considering the fact that the addition amount of rare earth in the alloy is very minute. The directional migration process and mechanism of cerium were discussed. First, the sinter skin （surface） is observed. oxide on the sinter skin, and lanthanum in these cerium observed, and lanthanum containing phase/micro-zone in It is shown that there exists a dispersedly distributed cerium containing enrichment positions is very minute. Secondly, the polished section is the alloy is identified. Finally, based on the fact that the fracture of cemented carbide is resulted from the heterogeneous phase or other defects within the microstructure, the fracture surface is observed and cerium containing phase/micro-zone in the fracture source approximately 260 μm from the surface is identified. These combined observations reveal adequately the fact that lanthanum and cerium get separated and cerium predominantly migrates towards the surface during the sintering process.展开更多
基金Project(52075103)supported by the National Natural Science Foundation of ChinaProject(2020B1515120058)supported by the Key Project of Regional Joint Fund of Guangdong Basic and Applied Basic Research Foundation,China。
文摘Ablation threshold is an important concept in the study of femtosecond laser micro-and nano-machining.In this paper,the ablation experiments of three kinds of surface roughness 4H-Si C substrates irradiated by femtosecond laser were carried out.The feature thresholds were systematically measured for three surface roughness Si C substrates and found in the modification and annealing regions ranging from coincidence(R_(a)=0.5 nm)to a clear demarcation(R_(a)=5.5 nm),eventually being difficult to identify the presence of the former(R_(a)=89 nm).Under multi-pulse laser irradiation,oriented ripple structures were generated in the annealing region,where deep subwavelength ripples(about 110 nm,Λ≈0.2λ)can be generated above substrates with surface roughness higher than 5.5 nm.We investigated the effect of surface roughness on the ablation morphology,ablation threshold,and periodic structures of femtosecond laser ablation of 4H-Si C substrates,while the ablation threshold was tended to decrease and stabilize with the increase of pulse number N≥500.
基金Project(50574104) supported by the National Natural Science Foundation of China
文摘Three observation methods were used to investigate the existing form and the behavior of rare earth during the sintering process of high activity mischmetal （RE, with lanthanum and cerium） doped WC-8%Co-0.048%RE（mass fraction） alloy with low carbon-containing level by scanning electron microscopy （SEM） and energy dispersive X-ray spectroscopy （EDXS）, considering the fact that the addition amount of rare earth in the alloy is very minute. The directional migration process and mechanism of cerium were discussed. First, the sinter skin （surface） is observed. oxide on the sinter skin, and lanthanum in these cerium observed, and lanthanum containing phase/micro-zone in It is shown that there exists a dispersedly distributed cerium containing enrichment positions is very minute. Secondly, the polished section is the alloy is identified. Finally, based on the fact that the fracture of cemented carbide is resulted from the heterogeneous phase or other defects within the microstructure, the fracture surface is observed and cerium containing phase/micro-zone in the fracture source approximately 260 μm from the surface is identified. These combined observations reveal adequately the fact that lanthanum and cerium get separated and cerium predominantly migrates towards the surface during the sintering process.
