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Laser-induced Si3N4–TiN ceramics degradation
摘要： This paper presents the process of degradation of the surface layer of Si3N4?TiN ceramics induced by a pulsed Nd:YAG laser. The dissociation of silicon nitride and titanium nitride in the irradiation zone is turned out to yield in a silicon depletion and so the zone becomes enriched with titanium, which, in turn, leads to the formation of TiSi2. This process of the TiSi2 formation can be considered as a ceramics metallization and its concentration depends on the energy delivered by the laser. The expansion of dissociation/evaporation products through the atmosphere is accompanied by the formation of SiO2 and TiO2, which are then deposited on the substrate as an amorphous ?lm of complex composition.
关键词： Surface phase transformation,(Si3N4 ? TiN):(Al2O3+Y2O3) ceramics,Film formation
更新于2025-09-12 10:27:22
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Growth of multi-morphology amorphous silicon oxycarbide nanowires during the laser ablation of polymer-derived silicon carbonitride
摘要： Multi-morphology amorphous SiOC nanowires were successfully prepared within the interfacial interstices between the una?ected SiCN ceramic and the bracket during the laser ablation of polymer-derived SiCN ceramic in a low-pressure argon atmosphere. Laser irradiation experiments were performed using a continuous-wave CO2 laser, and the gas source for the growth of amorphous SiOC nanowires was provided by the laser ablation of the SiCN ceramic. X-ray photoelectron spectroscopy shows that the amorphous SiOC nanowires possess a SiO2 dominated nanostructure, and the formation of amorphous SiOC nanowires is attributed to the good di?usivity of CO in SiO2. The morphologies of the amorphous SiOC nanowires include straight nanowires, beaded nanowires, helical nanowires, and branched nanowires, and these are determined by the ?owing state of the reactant gases, the laser power, and the surface morphology of the SiCN ceramics. Each amorphous SiOC nanowire with speci?c morphology can be uniformly distributed in separate regions, which makes it possible to control the growth of amorphous SiOC nanowires in di?erent morphologies.
关键词： Laser ablation,SiOC,Polymer-derived ceramics,Amorphous nanowires,Multi-morphology
更新于2025-09-12 10:27:22
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Investigations on vacuum sintered ytterbium-doped YAG ceramic: a laser–host material
摘要： Laser–host ceramics are a new class of materials and have proved to be a good alternative to the single-crystals. They can be produced in large size with higher concentration of activator ions having more homogeneity which is dif?cult to achieve with the conventional single-crystal growth technology. Ytterbium (Yb)-doped yttrium aluminium garnet (YAG) is a very attractive laser–host material because of its broad emission band, low quantum defect, no excited state absorption or up-conversion loss and wide range of tunability. In the present work, 10 atm% Yb-doped YAG transparent ceramic was fabricated using nano-powder technology and vacuum sintering. Single-phase nano-powders of Yb:YAG were synthesized by a co-precipitation method and thereafter sintered under vacuum at 1750?C for 5 h. The as-sintered ceramic samples are of dark greenish colour which is attributed to the reduction of Yb3+ to Yb2+ during vacuum sintering. However, after annealing in air at 1350?C for 8 h they retain their natural colour attributed to the transformations from Yb2+ to Yb3+. The transmission spectra of the as-sintered polished ceramics show the presence of broad absorption bands near 250, 380, 480 and 630 nm due to the electronic transitions in the Yb2+ ion. These bands disappear after annealing in air. The well-established bands due to transitions in Yb3+ were observed between 900 and 1000 nm.
关键词： sintering,Optical ceramics,Yb:YAG
更新于2025-09-12 10:27:22
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Prediction of surface roughness and material removal rate in laser assisted turning of aluminium oxide using fuzzy logic
摘要： Processing of ceramics with good surface integrity and high material removal rate is a challenging task in the manufacturing industry. Laser assisted machining (LAM) is one of the benchmark technique currently used in industry to process difficult to machine materials. In LAM, laser is used as source to heat the work piece and simultaneously remove the softened material by cutting tool without changing the material microstructure. Since many process parameters are involved in LAM, experimental investigation of processing of ceramics is expensive. So the main objective of this present work is to develop an Artificial Intelligence model to understand the process mechanics and for the prediction of surface roughness and material removal rate (MRR) during laser assisted turning of Aluminium oxide using fuzzy logic. Input parameters are assumed as triangular and Gaussian function and output parameters are assumed as trapezoidal function. It is inferred that increase in cutting speed and pulsed frequency of laser, there is an improvement in surface finish, whereas increase of feed rate results in deterioration of surface integrity. The material removal rate is directly proportional to feed, speed, depth of cut and pulsed frequency of laser. There is a better agreement between experimental and fuzzy model values. The proposed model predicts the surface roughness and MRR with prediction error of 15.76 and 7.69 % respectively.
关键词： material removal rate,Laser assisted machining,fuzzy logic,surface roughness,Ceramics
更新于2025-09-12 10:27:22
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Recent trends in laser assisted machining of ceramic materials
摘要： Machining of ceramics is difficult by conventional processes due to their hard and brittle nature as well as high costs involved. To overcome these disadvantages laser assisted machining (LAM) technique has been proposed. LAM has many advantages over conventional machining processes. LAM involves the use of a concentric beam of laser to heat and soften the work-piece thereby reducing its yield strength and increasing ease of machinability. With the progress of technology, numerous experiments involving LAM of ceramics have been performed and the effects of different machining parameters have been studied. In recent times, there have been various developments in laser technology, tools used and mechanisms of machining. This paper is intended to provide the elaborate literature review on the studies undergoing in LAM of ceramics and their comparison with conventional machining processes.
关键词： Laser assisted machining (LAM),tool life,laser,surface temperature,ceramics
更新于2025-09-12 10:27:22
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Photoinduced Modulation of the Emission from СdSe/ZnS Quantum Dots by Photochromic Transformations of Diarylethenes
摘要： A spectral study of the interaction between the molecules of photochromic compounds of the diarylethene class and CdSe/ZnS quantum dots (QDs), in dependence of the structure and nature of functional substituents of photochromes, has been performed. It is shown that both chemical and physical interactions are accompanied by photoinduced modulation of QD emission as a result of photochromic transformations of diarylethenes caused by the inductive transfer of excitation energy from QDs to the diarylethene cyclic isomer.
关键词： diarylethenes,CdSe/ZnS quantum dots,nanomaterials,photoinduced modulation,photochromic transformations,ceramics
更新于2025-09-12 10:27:22
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Femtosecond laser pulse ablation characteristics of polymer-derived SiAlCN ceramics
摘要： Polymer-derived ceramics (PDCs) are promising high-performance materials for various applications, yet their brittleness represents major drawback in their machining. Femtosecond laser pulse ablation is non-contact rapid processing method used in precision machining of PDCs. Herein, two laser parameters (laser energy fluence and rotational speed) were investigated to achieve laser–material interactions and machining characteristics via machine single circular lines, blind holes, and through-holes in polymer-derived SiAlCN ceramics. With the decrease in rotational speed, the morphology of single circular lines gradually roughened and heat-affected zone was produced. Varying ablation rates were obtained at different energy fluences. For blind holes, three different ablation regions were observed. As the energy fluence increased, blind holes gradually transformed into through-holes. Through-holes with near-cylindrical profiles and minimal collateral damage were obtained. Ablation debris deposited around through-holes were indicative of N release, breaking of Si-N and C-C bonds, and formation of SiOx. Laser ablation of PDCs led to the formation of laser-induced surface structures, bubble pits, stripe structures, molten materials, and sphere-like particles.
关键词： femtosecond laser pulse,ablation characteristics,polymer-derived ceramics,energy fluence
更新于2025-09-12 10:27:22
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Fabrication, microstructure and optical properties of Tm:Y <sub/>3</sub> ScAl <sub/>4</sub> O <sub/>12</sub> laser ceramics
摘要： Transparent 4 at.% Tm:Y3ScAl4O12 (Tm:YSAG) laser ceramics were fabricated by solid state reaction combined with vacuum sintering method. The 4 at.% Tm:YSAG ceramic sample sintered at 1800 oC for 30 h possesses homogenous microstructure and excellent optical properties, showing a transmittance of 79.3% at 2000 nm. The absorption and emission spectra of the Tm:YSAG ceramics are studied and compared with those of 4 at.% Tm:Y3Al5O12 ceramics. The introduction of Sc3+ greatly affects the energy levels of the Tm3+, causing the disappearance and degeneration of some absorption and emission peaks in the middle infra-red region. The laser performance of the 4 at.% Tm:YSAG ceramics is also tested in the Quasi-Continuous Wave (QCW) mode by pumping with a 790 nm laser diode (LD). A maximum laser output power of 0.54 W with a slope efficiency of 4.8% is achieved, which is the first laser output for Tm:YSAG ceramics.
关键词： Tm:YSAG,transparent ceramics,optical properties,microstructure
更新于2025-09-11 14:15:04
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High‐entropy transparent fluoride laser ceramics
摘要： For the first time, a transparent high‐entropy fluoride laser ceramic has been prepared and characterized. X‐ray diffraction (XRD) analysis of a CeNdCaSrBaF12 (CNCSBF) transparent ceramic consolidated by vacuum hot pressing (VHP) reveals that Ce3+, Nd3+, Ca2+, Sr2+, and Ba2+ have formed a single‐phased fluorite solid solution, with a lattice constant of 5.826??. Bulk density measurements produced a value of 6.15?g/cm3. Scanning electron microscopy (SEM) analysis of the ceramic revealed a uniform distribution of grain sizes in the material, with the average grain size being approximately 20?μm. The material exhibits a maximum in‐line transmittance of approximately 60% at 1000?nm. A near‐infrared range photoluminescence (PL) emission band was observed at 1057?nm, with a visible‐range PL emission band being located at 440?nm.
关键词： high entropy,transparent ceramics,optical properties,fluoride
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Novel Saturable Absorber: Transparent Glass-Ceramics Based on Co <sup>2+</sup> :Li(Al,Ga) <sub/>5</sub> O <sub/>8</sub> Spinel Nanocrystals
摘要： Cobalt ions (Co2+) embedded in tetrahedral (Td) sites are known for their intense absorption around 1.5 μm. Crystals such as spinel, MgAl2O4, doped with Co2+ ions in Td sites are recognized as excellent saturable absorbers (SAs) for eye-safe erbium lasers. Due to the relative difficulty to grow high-quality Co:MgAl2O4 crystals and fixed position of the Co2+ absorption band in spinel single-crystals, other Co2+-doped materials were proposed such as transparent glass-ceramics (GCs) and ceramics based on various spinels [1]. Transparent GCs offer a size-scalable synthesis method based on glass melting technology and variable spectroscopic properties as compared to crystals, and much higher laser induced damage threshold (LIDT) as compared to ceramics. GCs based on MgAl2O4 spinel nanocrystals modified by the addition of Ga3+ cations allow one to extend the SA properties until 1.7 μm [2]. In the present work, we describe the synthesis, structure, optical spectroscopy, nonlinear properties and passive Q-switching (PQS) performance of novel transparent GCs based on Co2+:Li(Al,Ga)5O8 nanocrystals. A lithium gallium aluminosilicate glass nucleated by TiO2 was doped with 0.1 mol% CoO. The GCs were produced by secondary heat-treatments at 680-850 oC for 6 h resulting in highly transparent, blue-colored samples, Fig. 1(a). The precipitation of nanosized spinel crystals was confirmed by XRD and TEM, Fig. 1(b,c), and Raman spectroscopy. The transparent GCs exhibited a broadband absorption band at 1.3-1.65 μm due to the 4A2(4F) → 4T1(4F) transition of Co2+ ions in Td sites in Li(Al,Ga)5O8 nanocrystals, Fig. 2(a). The saturable absoption of GC heat-treated at 750 oC for 6 h was studied by Z-scan method at 1540 nm using ns pulses. The saturation fluence FS is 0.50±0.05 J/cm2 and the LIDT exceeded 20 J/cm2, Fig. 2(b). This transparent GC was used to fabricate a SA for PQS of a compact diode-pumped Er,Yb:glass laser. This laser generated stable 7.4 ns / 1.34 mJ pulses at 1535 nm (peak power: 181 kW). The developed GC are promising as SAs for erbium lasers based on glass and crystalline materials (e.g., Er:YAG lasers emitting at 1617 nm and 1645 nm). This is because the broadband absorption of Co2+ ions in GCs is notably red-shifted as compared to Co:MgAl2O4 crystals which, in turn, is caused by the different spinel nanophase composition.
关键词： transparent glass-ceramics,Ga)5O8,Co2+:Li(Al,spinel nanocrystals,passive Q-switching,saturable absorber
更新于2025-09-11 14:15:04