Performance optimization of Si/SiC ceramic triply periodic minimal surface structures via laser powder bed fusion

SiC ceramic lattice structures (CLSs) via additive manufacturing (AM) have been recognized as potential candidates in engineering fields owing to their various merits. Compared with traditional SiC CLSs, SiC triply periodic minimal surface (TPMS) CLSs could possess more outstanding properties, making them more promising for wider applications. Since SiC CLSs are hard to be fabricated through stereolithography techniques because of inferior light performance, the laser powder bed fusion (LPBF) process via selective sintering is an effective method to prepare near-net-shaped SiC TPMS lattices. As the mechanical performances of lattice structures are the foundation for future practical applications, it is of great significance to optimize the preparation process, thus improving the mechanical properties of SiC TPMS structures. In this work, the optimal printing parameters of the LPBF and liquid silicon infiltration process for SiC ceramic TPMS CLSs with three different volume fractions were systematically illustrated and analyzed. The effects of the printing parameters and carbon densities on the fabrication accuracy, microstructure, and mechanical performance of SiC TPMS CLSs were defined. The mechanism of the reactive sintering process for the SiC TPMS lattice structure was revealed. The results reveal that Si/SiC TPMS CLSs with optimum preparation have superior manufacturing accuracy (most less than 6%), relatively high bulk densities (about 2.75 g/cm³), low residual Si content (6.01%), and excellent mechanical properties (5.67, 15.4, and 44.0 MPa for Si/SiC TPMS CLSs with 25%, 40%, and 55% volume fractions, respectively).     

Effects of ZrO2 nanoparticles on the microstructure and mechanical properties of ZrO2/AlSi10Mg composites manufactured by laser powder bed fusion

In this work, the nano-ZrO₂ particles were mixed into AlSi10Mg alloy to prepare ZrO₂/AlSi10Mg composites with different x wt.% ZrO₂ (x = 0, 0.15, 0.3, 0.45, 0.6, 0.75). The microstructure, mechanical properties and the anisotropy of the ZrO₂/AlSi10Mg composites fabricated by laser powder bed fusion (LPBF) were studied. The results show that nano-ZrO₂ particles can be uniformly dispersed on the AlSi10Mg powder by the method of pre-dispersion and mechanical mixing. When the mass ratio of ZrO₂ in ZrO₂/AlSi10Mg composites is 0.3 wt%, the values of the tensile strength, yield strength and elongation are 493.64 MPa, 321.30 MPa and 11.74%, respectively. Compared with AlSi10Mg alloy, the tensile strength of ZrO₂/AlSi10Mg composites with 0.3 wt% is increased by 30–55 MPa and the elongation is increased by 3–5%. In addition, the mechanical properties of AlSi10Mg alloy and ZrO₂/AlSi10Mg composites of 0.3 wt% exhibit antistrophic behavior in different direction, which is due to the differences of microstructure, texture and stress distribution between transverse direction (TD) and build direction (BD). Compared with other AlSi10Mg matrix composites, ZrO₂/AlSi10Mg composites of this work show excellent strength and plasticity matching.     

Correlation of reuse extent with degradation degree of PA 12 powder during laser powder bed fusion and mechanical behavior of sintered parts

The development of an effective powder utilization is key to maximizing the potential of polyamide 12 (PA 12) for commercial laser-based powder bed fusion of polymers (PBF-LB/P). This requires an extensive study of relationships between the powder reuse extent, macroscopic properties of the powder, and mechanical properties of sintered parts. This work investigates the effects of the extent of PA 12 powder reuse during PBF-LB/P on the powder's degradation degree and mechanical properties of the sintered parts. Powder reuse extent was expressed in terms of cumulative build time while degradation degree was assessed in terms of deviations in the properties of the reused powders from those of virgin powder. Increase in the powder reuse extent led to increased thickness of crystallite, melting temperature, and sintering window of the powder while the crystallization temperature, crystallinity degree, and melt flow rate decreased with increased reuse extent. The mechanical strength and modulus of the sintered parts initially decreased with an increase in number of build cycles to reach a minimum at the sixth build cycle, after which it increased. This study is a step further towards achieving an efficient PA 12 powder management and a systematic control of quality of sintered parts.     

Use of additives for porosity control in the manufacturing of MAX phase components by powder bed fusion processes

Porosity is a major concern in the manufacturing of MAX phase components through powder bed fusion process. Three factors, powder characteristics, processing parameters, and internal reactions have been identified as key factors governing densifications of these printed parts. While investigations on the first two factors are quite common, the last one seems less explored. In this study, micro-alloying (substitution) on the M-site was selected as a possible way of tuning the internal reaction. A lower diffusion material niobium was adopted as a substitutional component through the relation $(2-x)\mathrm{Ti}:(1+x)\mathrm{Al}:\mathrm{C}:y\mathrm{Nb}$,that combine three pre-existing concepts on powder mixture, including stoichiometric, near-stoichiometric, and the solid solution on M-site. Two powder mixtures in prescribed ratio related to two different combinations of x and y values arbitrarily chosen denoted by Nb1 and Nb3 were considered for investigation. A comparison of density and area fraction quantifying the distribution of pores and compact areas on the upper surface of the sample was made. A skeletal density of 94.85% and a compact area fraction of 68.24% were outstanding characteristics displayed in the Nb1 and Nb3 series, respectively, with a significant dependence on the processing parameters. The advantages and disadvantages of these two powder mixtures are discussed.     

One-step fabrication of Li2TiO3 ceramic pebbles using pulsed YAG laser

A large amount of Li-containing ceramic breeder pebbles is packed in the solid breeding blanket of a nuclear fusion reactor. Several pebble fabrication technologies have been proposed in previous studies, including wet process, emulsion method, extrusion spheronization, additive manufacturing, and melt process. However, a simple, energy-effective, and scalable fabrication technology remains to be developed for the automated mass production and reprocessing of used radioactive pebbles post-operation. Selective laser melting potentially enables the quick and automated fabrication of breeder pebbles. Herein, we employ a high-power density pulse laser to produce ceramic breeder pebbles. A pulsed YAG laser was irradiated over a lithium metatitanate (Li₂TiO₃) powder bed in air, and the corresponding temperature was monitored using fiber-type infrared pyrometers. Spherical Li₂TiO₃ pebbles were successfully fabricated in a single step with an average diameter of 0.78 ± 0.13 μm and the sintering density of 87.4% ± 5.6% (input power: 7.9 J/pulse). The irradiated Li₂TiO₃ powder melted and turned spherical under surface tension and rapidly solidified, resulting in uniaxial fine grains and a decrease in the degree of long-range cation ordering.     

Hierarchically porous alumina ceramic catalyst carrier prepared by powder bed fusion

Hierarchical porous ceramic catalyst carriers, which exhibit good catalytic performance, are widely used in the petrochemical industry. However, the fabrication of ceramic carriers with hierarchically porous structures is highly challenging for conventional preparation processes. Thus, a strategy for designing and manufacturing hierarchically porous alumina ceramic catalyst carriers using aluminium trihydrate as raw material and powder bed fusion (PBF) as the forming process is proposed herein. PBF process parameters were optimised to define the processing window for creating ceramics with complex structures. Controllable pore characteristics in nano- and microscales has been achieved by combining dehydroxylation, PBF, and post-sintering processes. The effects of raw material composition and process parameters on crush strength, porosity, and specific surface area were systematically investigated. The resulting porous ceramics exhibit a crush strength of 86.03 ± 18.10 N/cm, specific surface area of 1.958 ± 0.123 m²/g, and porosity of 64.85 ± 1.15% with a multipeak distribution at 95 ± 1.23 nm and 17.76 ± 0.14 μm. The possibility of complicated monolithic catalyst carrier structures with bionic leaf vein characters has been validated for potential industrial applications.     

Densification behaviour and three-dimensional printing of Y2O3 ceramic powder by selective laser sintering

The selective laser sintering (SLS) of an yttria (Y₂O₃) ceramic powder was studied to understand both the effects of i) the initial yttria particle characteristics on the powder bed behaviour and ii) the process conditions (laser power, scanning speed, hatching space) on the sintering/melting of three-dimensionally printed objects. The roughness of the powder bed, a sensitive indicator of the layer bed quality, was determined through three-dimensional optical profilometry and the powder bed packing density was modelled using the discrete-element method. Complex shaped objects including spheres and open rings were successfully fabricated by the SLS three-dimensional printing. In addition, SLS cube-shaped samples were characterized by X-ray diffraction and scanning electron microscopy. The open pore volume fraction significantly decreased from 41% without a post-SLS heat treatment to 31% with a post-SLS heat treatment at 1750 °C for 20 h under secondary vacuum. Finally, an anisotropy in elastic properties has been highlighted, Young's modulus reaches 11 GPa in the stiffest direction.     

Preparation of alumina/polystyrene core-shell composite powder via phase inversion process for indirect selective laser sintering applications

Indirect selective laser sintering (SLS) is one of the promising additive manufacturing (AM) methods that can process conventionally difficult or even impossible materials such as ceramics. In this work, an innovative phase inversion technique is used to fabricate spherical alumina particles coated with a thin layer of polystyrene (PS). Then, indirect SLS is used to fabricate green parts from the 6 wt% PS coated alumina particles via a Nd:YAG laser. The assessed SLS process parameters were the scan speed, laser power, scan spacing, pulse frequency, and pulse width. The characterization of the AL₂O₃/PS core-shell composite particles was described using techniques including SEM (for morphology), FT-IR (for chemical bonding at the interfaces), TGA (for mass loss), and DSC (for glass transition temperature, T_g). 3D green parts were then fabricated using proper process parameters as a proof of the feasibility of using SLS technique for AL₂O₃/PS core-shell composite powder. The results showed that using a Nd:YAG laser with less absorption by alumina and PS provides greater penetration through a powder bed. In addition, the possibility of sound connections among particles in every direction was observed due to the uniformity of the coating process in spite of a minimal amount of binder. In addition, green part density measurements show high values compared to previously reported results.     

Additive manufacturing of glass with laser powder bed fusion

Its transparency, esthetic appeal, chemical inertness, and electrical resistivity make glass an excellent candidate for small- and large-scale applications in the chemical, electronics, automotive, aerospace, and architectural industries. Additive manufacturing of glass has the potential to open new possibilities in design and reduce costs associated with manufacturing complex customized glass structures that are difficult to shape with traditional casting or subtractive methods. However, despite the significant progress in the additive manufacturing of metals, polymers, and ceramics, limited research has been undertaken on additive manufacturing of glass. In this study, a laser powder bed fusion method was developed for soda lime silica glass powder feedstock. Optimization of laser processing parameters was undertaken to define the processing window for creating three-dimensional multilayer structures. These findings enable the formation of complex glass structures with micro- or macroscale resolution. Our study supports laser powder bed fusion as a promising method for the additive manufacturing of glass and may guide the formation of a new generation of glass structures for a wide range of applications.     

重防腐熔结环氧粉末涂料与涂装

系统介绍了重防腐熔结环氧粉末涂料的特性、分类、涂装技术、涂料制造技术、主要原材料、涂层的检测标准和试验方法。     

Improved thermal conductivity of sintered reaction-bonded silicon nitride using a BN/graphite powder bed

Sintered reaction-bonded silicon nitride (SRBSN) with improved thermal conductivity was achieved after the green compact of submicron Si powder containing 4.22 wt% impurity oxygen and Y₂O₃-MgO additives was nitrided at 1400 °C for 6 h and then post-sintered at 1900 °C for 12 h using a BN/graphite powder bed. During nitridation, the BN/10 wt% C powder bed altered the chemistry of secondary phase by promoting the removal of SiO₂, which led to the formation of larger, purer and more elongated Si₃N₄ grains in RBSN sample. Moreover, it also enhanced the elimination of SiO₂ and residual Y₂Si₃O₃N₄ secondary phase during post-sintering, and thus induced larger elongated grains, decreased lattice oxygen content and increased Si₃N₄-Si₃N₄ contiguity in final SRBSN product. These characteristics enabled SRBSN to obtain significant increase (∼40.7%) in thermal conductivity from 86 to 121 W ∙ m⁻¹ ∙ K⁻¹ without obvious decrease in electrical resistivity after the use of BN/graphite instead of BN as powder bed.     

Powder bed selective laser processing (sintering / melting) of Yttrium Stabilized Zirconia using carbon-based material (TiC) as absorbance enhancer

This study aimed to process 8 mol.% yttrium stabilized zirconia by powder bed selective laser processing, as well known as selective laser sintering / melting. Titanium carbide was used as absorbance enhancer to a Nd:YAG laser. Titanium carbide was chosen for having the lowest weight / absorbance ratio among four additive options: silicon carbide, carbon black, graphite, and titanium carbide. Several trials were performed using 0,25 wt.% of titanium carbide as absorbance enhancer of 8 mol.% yttrium stabilized zirconia, testing different laser powers, laser speeds, laser strategies, hatch distances and designs. A window of optimized parameters was identified within the study conditions, capable of manufacturing parts with high relative density. In addition, challenges and technical aspects are discussed by analyzing the observed phenomena.     

Numerical simulation on evolution process of molten pool and solidification characteristics of melt track in selective laser melting of ceramic powder

A three-dimensional high-fidelity physical model for selective laser melting (SLM) of ceramic powder was created based on computational fluid dynamics (CFD) to examine the physical mechanism of molten pool and solidified tracks at mesoscopic scale. The discrete element method (DEM) was used to generate a randomly packed powder bed, and the volume-of-fluid method (VOF) was applied to dynamically monitor the free surface of the molten pool. The formation mechanism and evolution characteristics of the molten pool were found and analyzed, and the effects of laser power on the typical characteristics of solidified ceramic tracks of SLM were investigated. The molten pool was eventually solidified into a concave geometric shape track by surface tension. The laser power played a significant impact on the shaping quality of solidified ceramic track. When the laser power was too low, the melt track suffers from severe porosity and distortion defects, which can be effectively solved with increasing laser power. The simulation results were validated via single track selective laser melting of TiC ceramic powder.     

Direct laser additive manufacturing of high performance oxide ceramics: A state-of-the-art review

The implementation of additive manufacturing for ceramics is more challenging than for other material classes, since most of the shaping methods require polymer binder. Laser additive manufacturing (LAM) could offer a new binder-free consolidation route, since it is capable of processing ceramics in a direct manner without post-processing. However, laser processing of ceramics, especially high performance oxide ceramics, is limited by low thermal shock resistance, weak densification and low light absorptance at room temperature; particularly in the visible or near-infrared range. An extensive review focusing only on LAM (powder bed fusion – laser beam and directed energy deposition) of high performance oxide ceramics is currently lacking. This state-of-the-art review gives a detailed summary and critical analysis about process technologies, part properties, open challenges and process monitoring in the field of oxide ceramics. Improvements in accuracy and mechanical strength are proposed that could open LAM of oxide ceramics to new fields.     

钢质管道防腐用熔结环氧粉末固化反应特性

采用示差扫描量热法(DSC)在动态条件下研究了钢质管道防腐用熔结环氧粉末的反应特性,根据不同升温速率下测得的动态DSC曲线图谱,运用温度-升温速率(T-β)图外推法获得了基础的固化工艺参数,即凝胶温度(Tg)92.76℃、固化温度(Tc)133.94℃和后处理温度(Tt)160.58℃。并采用Kissinger方程和Crane公式计算确定了体系的固化反应动力学模型方程式,在此基础上,预测了等温条件下该种管道用熔结环氧粉末涂料的固化反应特性,对今后的管道防腐涂层施工提供了理论参考。     

Spherical cellulose–nickel powder composite matrix customized for expanded bed application

Expanded bed adsorption (EBA) is an integrated technology for capturing target biomolecules directly from particle‐containing feedstock. The adsorbents are the key base to achieve the EBA process and should be designed specially. In present work a new type of composite particles for EBA application was prepared with cellulose as the skeleton, and nickel powder as the densifier through the method of water‐in‐oil suspension thermal regeneration. Two fractions of spherical particles with mean sizes of 101–119 μm and 168–217 μm were obtained and the effects of nickel powder addition on the physical properties of composite particles were analyzed. The results indicated that the cellulose–nickel powder composite particles prepared have appropriate wet density of 1.14–1.78 g/mL, water content of 51–75%, porosity of 81–93%, pore radius of 41–59 nm, and specific surface area of 30–42 m²/mL of wet particles. The bed expansion factor at the range of 2–3 was investigated and correlated with Richardson–Zaki equation. In addition, the bed stability with composite particles prepared was demonstrated with the observation of liquid mixing in expanded bed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 740–747, 2007     

Easysizer20型激光粒度仪测定炭素粉末粒度分析

在电碳工业研究中,炭素粉末粒度的分析是炭素材料的重要技术指标之一,是炭素制品研究人员对工艺创新,提高产品质量的重要保证。本文通过激光粒度分析仪对石墨粉粒度测量进行的重复性试验,测试结果分析表明：激光粒度仪适合碳素粉末的粒度测量,同时讨论了激光粒度仪测量误差的主要来源,即来自仪器测量本身与测试前样品处理过程两个方面,其中样品处理过程是粒度测量中误差的主要来源。     

Crack-reduced alumina/aluminum titanate composites additive manufactured by laser powder bed fusion of black TiO2−x doped alumina granules

Laser powder bed fusion is an emerging industrial technology, especially for metal and polymer applications. However, its implementation for oxide ceramics remains challenging due to low thermal shock resistance, weak densification and low light absorptance in the visible or near-infrared range. In this work, a solution to increase the powder absorptance and to reduce cracking during laser processing of alumina parts is given. This is achieved by the use of a homogeneously dispersed and reduced titanium oxide additive (TiO_2?x) within spray-dried alumina granules leading to formation of aluminum titanate with improved thermal shock behavior during powder bed fusion. The impact of different reduction temperatures on powder bed density, flowability, light absorption and grain growth of these granules is evaluated. Crack-reduced parts with a density of 96.5%, a compressive strength of 346.6 MPa and a Young's modulus of 90.2 GPa could be manufactured using powders containing 50 mol% (43.4 vol%) TiO_2?x.     

选择性激光烧结用聚合物基材料制备研究进展

选择性激光烧结（selective laser sintering, SLS）是一种重要的3D打印加工技术,可制备传统加工无法制备的任意复杂形状的制件,广泛应用于航空航天、国防装备、医疗器械以及汽车等高新技术领域。本文介绍了SLS技术的加工原理和优势,综述了SLS技术加工成形用材料种类及聚合物基粉体材料的制备方法,主要包括相分离法、机械粉碎法、溶液法和喷雾干燥法。重点对SLS技术制备聚合物基压电复合材料及制品的国内外研究现状进行总结。虽然SLS打印制造技术面临聚合物原料种类少、功能缺乏、粉体生产成本高以及难以批量制备等瓶颈问题,但经过不断地创新与发展,SLS打印技术将成为高性能多功能高分子复合材料及其大型复杂制件的极佳制造方法。     

Adhesives for bead fusion of recycled expandable polystyrene

Expandable polystyrene (EPS) is a plastic cellular material that is commonly used in the packaging industry. Its growing uses have led to environmental concerns over resource sustainability and the dwindling availability of landfill spaces. Although existing approaches to control and manage EPS wastes are available, much effort is still needed to recycle as much of the used materials via developing new processes or applications. This article looks into a new approach using adhesives to promote EPS bead fusion. Two sets of test specimens made of 100% recycled EPS using spray adhesive and powder adhesive were investigated. Their mechanical behaviors of these two adhesive EPS samples were studied. These specimens were compared with the commercially available ones produced using steam injection molding and direct microwave molding. From the findings, the powder adhesive specimens were found to be quite comparable to the steam‐injected ones in terms of better cushioning property, shape definitions, smaller dimensional and density variations than those of sprayed adhesive and microwave ones. The results highlight that powder adhesive mixed with 100% recycled EPS offer a new “green” approach in EPS production with low initial capital outlay and shorter production lead time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 456–462, 2002