Effect of annealing on quality enhancement of micro-machining green alumina ceramics by laser ablation

The natural characteristics of sintered ceramics limit the micromachining of functional surface textures in terms of tool wear, processing quality and economic effectiveness. So, the micro-machining of green ceramics before completely sintering is introduced. In this paper, micro-channels are fabricated on the surfaces of green ceramics pretreated by different annealing temperatures. The effect of parametric combination of annealing temperature and laser parameters on the response of processing quality, channel dimension and material removal rate (MRR) are studied by single fact experiments and multi-objective optimization by the response surface method (RSM). The mathematical models of the interaction between different factor combinations are developed based on RSM. Results show that the annealing temperature has significant influence on the aspect ratio under different laser parameters. Continuous channels with few recast layers are always formed at the annealing temperatures of 500–800 °C and a higher annealing temperature always contributes to a larger aspect ratio. Based on the responses of RSM, the optimal parameters of laser ablation and annealing temperature are chosen as laser power of 6 W, scanning speed of 350 mm/s, laser frequency of 40 KHz, and the pretreatment annealing temperature of 750 °C. The experiments validate good agreement of proposed model.     

Deep precision machining of SiC ceramics by picosecond laser ablation

Silicon carbide (SiC) ceramic is becoming widely used in multiple industrial applications, owing to its exceptional high-temperature properties. Yet it is still a challenge to machine SiC using traditional means without causing damage due to its high hardness and brittleness. In this study, a subtractive manufacturing technique based on the use of a fiber picosecond laser was employed to remove material from the reaction bonded SiC surface or create micro-patterns with the minimum damage to the surface, maximum surface quality and precision. Multiple laser processing parameters were investigated with the purpose of obtaining deep high-quality cuts with the minimum surface roughness and the minimum amount of the re-deposited material. The heat affected zone was analyzed by grazing angle X-ray diffractometry, cross-sectional scanning electron microscopy, energy dispersive and micro Raman spectroscopy techniques. The cut shape, depth, surface roughness as well as the kerf width and re-deposition height were assessed using a 3D laser scanning microscopy. The optimum values were established for the focal position, the laser power, linear speed, wobble frequency, wobble pattern, and number of passes. This study also identified the processing parameters for shallow and deep high-precision SiC cutting at a material removal rate of ～2 mm³/min. The work demonstrated that the developed laser machining process is an efficient subtractive manufacturing tool that can be integrated into the automated precision cutting systems for machining hard ceramic materials such as SiC and alumina.     

Fabrication of grooves on polymer-derived SiAlCN ceramics using femtosecond laser pulses

In this study, grooves were fabricated on the surface of fully dense polymer-derived SiAlCN ceramics. Industrial femtosecond laser source was used at wavelength of 1030 nm with pulse duration of 290 fs and repetition rate of 100 kHz. Moreover, comprehensive study was carried out to evaluate the influence of scan speed and energy fluence on grooves quality, including the heat-affected zone around the laser-machined grooves, microstructures of laser-irradiated surface, and cross-section morphology of grooves. A series of grooves with width in the range of 30–80 μm and depth below 280 μm was successfully fabricated using femtosecond laser pulse. Laser parameters were optimized to obtain grooves with satisfying surface quality. Furthermore, formation and disappearance of laser-induced periodic surface structures were systematically investigated. This study proposes fabrication of grooves on SiAlCN ceramics via laser processing, which provides precise method for fabrication of microstructure with fascinating properties.     

Fabrication of coloured zirconia ceramics by infiltrating water debound injection moulded green body

Abstract

Abstract

The authors developed a new technique combining ceramic injection moulding and liquid precursor infiltration, presenting a new strategy for fabrication of coloured zirconia ceramics. The authors’ strategy includes ceramic injection moulding 3Y‐TZP powder using a water debinding binder system, debinding moulded parts in water and drying, immersing debound parts in solutions containing different colouring ions and then sintering and creating coloured zirconia ceramics. The fabricated coloured ceramic bars exhibit a core shell structure, and the thickness of the coloured shell can be tailored by adjusting immersion time and temperature. Using solutions containing different colouring ions, ceramic bars with various colours can be prepared.     

脉冲激光轰击法连续制备纳米铜研究

采用脉冲激光轰击法连续制备了纳米铜及表面活性剂原位修饰的油溶性纳米铜,用UV-Vis研究了不同表面活性剂不同浓度对纳米铜／乙醇溶胶的紫外-可见光谱的影响,从而确定各表面活性剂的最佳浓度,用TEM研究了不同表面活性剂对纳米铜溶胶分散稳定性的影响,确定了最佳表面活性剂为平平加O,傅立叶红外光谱发现纳米铜／乙醇溶胶中乙醇分子基团振动波长受纳米铜颗粒的影响而出现红移现象,分散性实验表明：平平加O表面修饰纳米铜具有良好的油溶性。     

Fabrication and laser performances of Yb:Sc2O3 transparent ceramics from different combination of vacuum sintering and hot isostatic pressing conditions

In this paper we report on the preparation and laser performance of transparent 3at.% Yb:Sc₂O₃ ceramics by reactive sintering of commercially available powders under vacuum followed by hot isostatic pressing (HIP). Combinations of different vacuum sintering temperatures (1650 °C and 1750 °C) and different HIP treatments (1700 °C and 1800 °C at 200 MPa) were tested in order to understand how these steps influence the microstructure and thus the optical and lasing properties of the ceramic samples. All the samples showed a good optical quality. The microstructure analysis and the laser tests showed that the vacuum pre-sintering temperature is the key factor determining the quality of the samples and the laser performances. The best values of slope efficiency i.e. η_L = 50 % and output power i.e. P_out = 6.62 W were obtained for the sample pre-sintered under vacuum at 1650 °C and hot isostatically pressed at 1800 °C.     

织构PNN-PZT陶瓷的光固化成型制备及其电学性能研究

为高效制备织构压电陶瓷,以球状Pb(Ni_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PNN-PZT) 为基体粉体,片状BaTiO₃ （BT）为模板粉体,采用光固化成型技术代替传统流延技术制备织构压电陶瓷。研究了粉体形貌对打印浆料流动性的影响、浆料的光敏参数以及不同BT含量织构陶瓷的晶体结构和电学性能。结果表明,球状粉体浆料具有低黏度的特性,能够有效提高打印浆料的固含量,最大固含量可达86%（质量）。此时陶瓷浆料的临界曝光量与透射深度分别为127.5 mJ/cm²和21.1 μm。打印后的PNN-PZT-BT陶瓷沿[00l]_c方向生长,BT模板粉体含量从1%增长到5%,陶瓷的织构度由42%增到92%。当BT含量为3%时,样品具有最高的压电常数d₃₃=1047 pC/N。与传统的流延法相比,SLA技术的工艺优势在于制备周期短,稳定性高,能够有效降低织构陶瓷的制备难度。     

织构PNN-PZT陶瓷的光固化成型制备及其电学性能研究

为高效制备织构压电陶瓷,以球状Pb(Ni_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ (PNN-PZT) 为基体粉体,片状BaTiO₃ （BT）为模板粉体,采用光固化成型技术代替传统流延技术制备织构压电陶瓷。研究了粉体形貌对打印浆料流动性的影响、浆料的光敏参数以及不同BT含量织构陶瓷的晶体结构和电学性能。结果表明,球状粉体浆料具有低黏度的特性,能够有效提高打印浆料的固含量,最大固含量可达86%（质量）。此时陶瓷浆料的临界曝光量与透射深度分别为127.5 mJ/cm²和21.1 μm。打印后的PNN-PZT-BT陶瓷沿[00l]_c方向生长,BT模板粉体含量从1%增长到5%,陶瓷的织构度由42%增到92%。当BT含量为3%时,样品具有最高的压电常数d₃₃=1047 pC/N。与传统的流延法相比,SLA技术的工艺优势在于制备周期短,稳定性高,能够有效降低织构陶瓷的制备难度。     

A comparative investigation on micro-channel by using direct laser ablation and liquid-assisted laser ablation on zirconia

In this work, direct laser ablation (DLA), liquid-assisted laser ablation in water (LALA-W) and in ethanol (LALA-E) is applied to fabricate single micro-channels on the zirconia ceramic by using a picosecond laser. To assess the machining ability of them, micro-channels fabricated are characterized and compared the differences in morphology, geometric profile, chemical and phase composition. The morphological results indicate that both LALA-E and DLA can fabricate microchannel with obvious recast layer and cracks, and LALA-W can fabricate microchannel with a porous surface, and almost no recast layer and cracks. The results of geometric characteristics show that LALA-W can fabricated micro-channels with “U” shape profile with 52.74% enhancement in depth compared to that “V” shape by DLA and LALA-E. The XPS results demonstrate that LALA-W can exhibit the smallest oxygen vacancies with 50.01% than that of LDA 53.81% and LALA-E 54.56%. For XRD results, after machining by all three processes, the zirconia ceramic undergoes the tetragonal→monoclinic phase transformation, resulting in an increase in monoclinic phase. While LALA-W exhibits the smallest increase in monoclinic phase from 9.9% to 12.7%, and has the most tetragonal phase content of 58.8%.     

Simulation and experimental study on group hole laser ablation on AL2O3 ceramics

Thermal effect is inevitable during laser processing and is easy to induce cracks and damage on the hard and brittle materials, especially. The crack generation mechanism during laser ablation of single hole and groups of holes on alumina ceramic has been investigated. A heat conduction model of the nanosecond laser processing of a group of holes has been developed. The temperature field over a AL₂O₃ sample was modeled and simulated using COMSOL multi-physics. The temperature distribution on the AL₂O₃ sample was experimentally verified using an infrared thermometer. The present research provides guidance for the high-quality laser machining of group holes over large areas.     

Laser sintering of Al2O3-based green ceramics prepared by different pre-sintering temperatures

Al₂O₃-based green ceramics are prepared by isostatic cold pressing technology. The prepared green ceramics are pre-sintered at the temperature from room temperature to 1100°C, and then Al₂O₃ ceramics are prepared by laser sintering. The effects of pre-sintering temperatures and laser parameters on mechanical properties and the sintering quality are analyzed. The results show that good crystallinity of Al₂O₃ particles is obtained at a higher pre-sintering temperature. The flexural strength and density of green ceramics increase with the temperature of heat treatment. The flexural strength decreases slightly at ∼200°C due to the paraffin binder disintegration. The pre-sintering temperature and laser processing parameters have a significant influence on the sintering quality. With the increase of laser power and laser frequency, dynamic grain growth occurs, and then grains are refined. The majority of plate-like grains are transformed into long cylindrical-like grains in the severe densification process. However, porous flocculation microstructures are generated on the samples pre-sintered at 1100°C after laser sintering, which is due to the material gasification in atmospheric environment during sintering by infrared laser. More uniform microstructure and better sintering quality of samples pre-sintered at 500°C can be achieved after laser sintering with a relatively narrower grain size distribution.     

Thermal stability and nanostructure evolution of amorphous SiCN ceramics during laser ablation in an argon atmosphere

The thermal stability and nanostructure evolution of amorphous SiCN ceramics during laser ablation in an argon atmosphere were investigated. Laser irradiation experiments were performed by using a continuous wave CO₂ laser, and a finite element simulation was conducted to quantify the non-uniform temperature field during the laser irradiation. Three regions with different ablation behaviours were identified based on the radial temperature gradient. Cracks extended through these three regions because of the large thermal stress. In the reaction zone, the SiCN ceramic surface was covered by only porous SiC because of the carbothermic reaction. In the transition zone, a weak carbothermic reaction occurred at the surface of the SiCN particles, but the graphitisation of the carbon nanostructure was enhanced dramatically. The heat affected zone showed no change in the microstructure morphology. However, the carbon nanostructure also exhibited higher graphitization.     

Fabrication and laser oscillation of Yb:Sc2O3 transparent ceramics from co-precipitated nano-powders

Ytterbium doped scandium oxide (Yb:Sc₂O₃) transparent ceramics were fabricated by a co-precipitation and vacuum sintering method. The characteristics of the precursor and the calcined powders were investigated by BET, XRD, and SEM. Ultra-fine and low agglomerated 5at%Yb:Sc₂O₃ powders with the average particle size about 65.4 nm were obtained after calcined at 1100 °C for 5 h. Using the synthesized powders as starting materials, 5at%Yb:Sc₂O₃ transparent ceramics with the in-line transmittance of 71.1% at 1100 nm and average grain size of 145 μm were fabricated by vacuum sintering at 1825 °C for 10 h. Quasi-CW laser oscillation of Yb:Sc₂O₃ ceramics was obtained at 1040.6 nm. A maximum output power as high as 2.44 W with a corresponding slope of 35% was achieved. Finally, the tunability of the ceramic was explored measuring a tuning range up to 55 nm.     

Effect of temperature on sulfur-doped diamond-like carbon films deposited by pulsed laser ablation

In this study, S-DLC films were deposited using pulsed laser ablation of a novel sulfur-graphite (SG) mixture target using an ArF excimer laser (193 nm). The SG targets were made by mixing sulfur and graphite powders at different sulfur molar percentages from 0% to 25%. The S-DLC films were deposited at room temperature, 150 °C and 250 °C. The optical and electronic properties of the doped films were studied. Laser Raman spectroscopy indicated increased graphitic behavior with temperature but decreased with higher sulfur content. Spectroscopic ellipsometry analyses found that the optical band-gap energy, extinction coefficient and reflective index, clearly depended on deposition temperature and sulfur content. Hall Effect measurements indicated n-type carrier with concentration in the range of 1 × 10¹⁴ to 2 × 10¹⁷ cm^− 3, strongly depended upon the deposition temperature and amount of sulfur.     

Fabrication of silver nanoparticles dispersed in palm oil using laser ablation

In this study we used a laser ablation technique for preparation of silver nanoparticles. The fabrication process was carried out by ablation of a silver plate immersed in palm oil. A pulsed Nd:YAG laser at a wavelength of 1064 nm was used for ablation of the plate at different times. The palm coconut oil allowed formation of nanoparticles with very small and uniform particle size, which are dispersed very homogeneously within the solution. The obtained particle sizes for 15 and 30 minute ablation times were 2.5 and 2 nm, respectively. Stability study shows that all of the samples remained stable for a reasonable period of time.     

Polymerization of monomers initiated by silyl centers in SiO deposits prepared by pulsed laser ablation

Deposits from silicon monoxide prepared by pulsed laser ablation were allowed to react with acrylic and vinyl monomers—styrene, methyl methacrylate and 1,2 ethylene glycol dimethacrylate. It was revealed by means of FTIR, electron paramagnetic resonance (EPR), and NMR spectroscopies that silyl ?Si· reacts with monomer molecules and initiates the consecutive polymerization. Crosslinking is proved by the occurrence of bending δ(? CH₂) absorption peak at about 750 cm^?1 in FTIR spectra. Because of very low concentration of the propagating radical for styrene we used a radical scavenger N‐phenyl‐t‐butylnitrone for trapping. The measured EPR parameters were compared with the calculated ones. In case of styrene, NMR analysis manifested the presence of Si? C bonds in SiC_xO_y (x + y = 2) units, which can be taken as direct evidence of the reaction between silyl centers and monomer molecules. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4488–4492, 2006     

Fracture toughness of zirconia from a shallow notch produced by ultra-short pulsed laser ablation

Fracture toughness of submicron grain size tetragonal zirconia polycrystals doped with 3 mol% yttria (3Y-TZP) is measured by the single edge V-notch beam (SEVNB) method from a shallow sharp notch produced by ultra-short pulsed femtolaser ablation (UPLA) on the surface of a bending bar. It is shown that the radius of the notch tip achieved is in the submicron range and the damaged volume in front of the notch tip is characterized by using focus ion beam milling and scanning electron microscopy. It consists of a narrow fully microcracked region less than ∼4 μm wide and ∼15 μm deep in front of the notch. If the extension of this region and the length of the notch are used in the determination of the fracture toughness (K_Ic) in the four bending test, the values obtained for submicron grain size 3Y-TZP are in agreement those obtained by using very sharp cracks. It is concluded that the SEVNB testing method with a sharp notch induced by UPLA may be used for K_Ic testing of submicron grain size ceramics.     

Fabrication and properties of novel composite laser ceramics with a surface-gain structure

To suppress heat effects in a high-power laser system, it has been proposed to use a few composite laser gain media to improve the heat management ability. The surface-gain structure has the advantages of both slab and thin-disk configurations, which has huge potential in high-power laser. For the first time, novel composite laser ceramics with surface-gain structure have been fabricated by tape casting and sintering technology. The in-line transmittances of surface-gain ceramics in 1100 and 400 nm are 83.5% and 79.1%, respectively. According to the laser ablation–coupled plasma mass spectrometry, the diffusion distance of Yb³⁺ is about 150 µm. The laser experiment yields a low repetition rate pulse of 1.9 J with a pump absorption energy of 11 J and an optical-to-optical conversion efficiency of 17.2%.