二氧化硅含量对光固化硅基陶瓷微观组织及性能的影响

以硅基陶瓷为研究对象,通过调整浆料内固相二氧化硅陶瓷粉末的体积分数(40%、42%、44%、46%、48%和50%)来控制浆料浓度,使用光固化快速成型技术获得不同二氧化硅含量的样品。采用扫描电子显微镜和高温抗折强度测试仪研究固相含量对光固化硅基陶瓷型芯微观形貌和力学性能的影响。结果表明,经光固化成形和1 300℃烧结后,样品收缩率和孔隙率随SiO_2含量增加而降低;抗折强度随SiO_2含量增加而增强。     

光固化3D打印SiC：粉体氧化处理提升浆料UV固化性能

为了进行碳化硅(SiC)的光固化3D打印,本文提出采用表面氧化处理提升SiC浆料的光固化性能。采用扫描电子显微镜、X射线衍射仪、X射线光电子能谱等研究了SiC颗粒的氧化过程以及氧化温度与保温时间对氧化过程的影响;采用动态流变仪、紫外分光光度计、数字千分尺等研究了浆料的流变性能和光固化性能。结果表明：经表面氧化处理后的SiC颗粒紫外反射率有显著的提高,最高为48.11%,为未氧化SiC颗粒的1.8倍;配制的浆料光固化性能有明显的改善,曝光5 s时固化厚度最高为76μm,为未氧化的3.6倍。随着氧化温度的上升以及保温时间的延长,氧化层厚度持续增长,最高达到144.8 nm。考虑到过度氧化不利于后续SiC陶瓷的烧结成型,最终选择使用1100℃保温3.0 h的氧化SiC粉末,并以1%(质量分数)的KOS163为SiC浆料的分散剂,制备了固含量为45%(体积分数)的SiC浆料,成功实现了SiC陶瓷坯体的光固化3D打印。     

聚氨酯模板法低温制备氧化铝泡沫陶瓷过滤器

利用聚氨酯海绵浸渍电熔氧化铝粉末与磷酸二氢铝制成的浆料,得到挂浆素坯,素坯经800℃热解制备了氧化铝泡沫陶瓷过滤器。研究了磷酸二氢铝含量对氧化铝泡沫陶瓷微观形貌、体积密度、线收缩率与抗折强度的影响。结果表明:磷酸二氢铝含量低于10%时,制备的泡沫陶瓷孔筋存在断筋与坍塌缺陷,力学性能较差;随磷酸二氢铝含量的增加,泡沫陶瓷的线收缩率有轻微增大,而体积密度与抗折强度都大幅提高,在磷酸二氢铝含量为30%时,可制得线收缩率为0.85%、体积密度为1.21 g/cm3、抗折强度达4.55 MPa的氧化铝泡沫陶瓷。     

复杂精密铸件整体式陶瓷铸型间接自由成形工艺

将光固化成形技术和凝胶注模成型技术结合在一起,提出了一种面向复杂精密铸件整体式陶瓷铸型间接自由成形新工艺。讨论了水基陶瓷浆料制备、光固化树脂原型工艺系统设计策略及其热解工艺、陶瓷坯体烧结等问题,并以空心涡轮叶片为实例,证实了新工艺的可行性和有效性。     

多层片式PTCR热敏陶瓷注凝成型工艺

研究了用注凝成型工艺制备片式PTCR热敏陶瓷.采用PMAA-NH4为分散剂,丙三醇为增塑剂,并加入适量的有机单体AM制备了高固相含量、低粘度的BaTiO3半导瓷浆料,研究了浆料粘度及坯体的性能与浆料固相体积分数、有机单体含量及增塑剂含量之间的关系.研究表明:浆料固相体积分数对坯体的干燥及烧结行为有较大影响,当浆料固相体积分数在45%以上时,可有效避免制品干燥和烧结过程中收缩过大而产生的变形开裂缺陷;当有机单体的质量分数为2%～4%,丙三醇的体积分数为3%～6%时,可获得有一定强度和柔韧性的生坯;研究了注凝成型PTCR陶瓷的微观结构及陶瓷元件的PTCR性能,成功地制备了层数为5、室温电阻为0.8Ω、电阻温度系数为13.40%/℃、升阻比大于105的多层片式PTCR元件.     

水基凝胶注Ti-6Al-4V合金坯体

将凝胶注模工艺应用于金属Ti6Al4V合金粉末的成形,研究了高固相含量的Ti6Al4V合金粉末的料浆的制备,比较了金属浆料与陶瓷浆料的不同。结果表明粉末的颗粒形状是影响浆料固相含量的重要因素,浆料的固相含量随分散剂的增加而增加。最后制备出了固相含量为54%(体积分数,下同)的钛合金粉末浆料和形状复杂的坯体。坯体的抗弯强度随气雾化(GA)Ti6Al4V含量增加先增大后减小,随着坯体的固相含量增大而减小。当GA-Ti6Al4V含量为80%,固相含量为50%时生坯抗弯强度最大,为18.5 MPa。     

工艺参数对Mo/Cu粉末凝胶注模成形的影响（英文）

采用甲基丙烯酸羟乙酯(HEMA)-1,6-己二醇二丙烯酸酯非水基凝胶注模体系制备了浓Mo/Cu粉末浆料。研究了分散剂用量、单体含量和固相体积分数对浆料流变行为的影响,并讨论了单体含量、单体/交联剂比例、引发剂用量、温度等工艺参数对固化行为和坯体抗弯强度的影响。结果表明,固相体积分数对浆料流变行为的影响最大,其次是引发剂用量和单体含量。随着单体含量的增加和单体/交联剂比例的减小,坯体抗弯强度增加;引发剂用量对坯体抗弯强度的影响较小。根据上述结果,Mo/Cu粉末非水基凝胶注模的合理工艺参数如下:HEMA含量为25%~30%(体积分数),单体/交联剂比例为10:1~15:1,引发剂用量为1.5%~2.5%(体积分数),固化温度在60~80℃之间。     

工艺参数对Mo/Cu粉末凝胶注模成形的影响

本文采用甲基丙烯酸羟乙酯（HEMA）-1,6-己二醇二丙烯酸酯非水基凝胶注模体系制备了浓Mo/Cu粉末浆料。研究了分散剂用量、单体含量和固相体积分数对浆料流变行为的影响。并研究了单体含量、单体/交联剂比例、引发剂用量、温度等工艺参数对固化行为和坯体抗弯强度的影响。结果表明,固相体积分数对浆料就变行为的影响最大,其次是引发剂用量和单体含量。随着单体含量的增加和单体/交联剂比例的减小,坯体抗弯强度增加;引发剂用量对坯体抗弯强度的影响较小。根据上述结果,Mo/Cu粉末非水基凝胶注模的合理工艺参数如下：HEMA含量为25 vol.% ~ 30 vol.%, 单体/交联剂比例为10：1 ～ 15：1,引发剂用量为1.5 vol.% ~ 2.5 vol.%,固化温度在60℃与80℃之间。     

胶态成型优化工艺制备氮化硅陶瓷及耐磨机理

以氮化硅粉末为原料,利用胶态注浆成型制备出先进耐磨陶瓷材料.统计模式识别分析可得目标优化区域,经逆映射法预报了未知区域中的工艺参数并得到第2次实验验证.进一步的实验研究还表明,当浆料中固相体积分数为40%时,可制得高密度素坯,其烧结体断裂韧性达7.19 MPa·m1/2,优于传统干压成型法(～6.2 MPa·m1/2).抗磨损实验研究表明,氮化硅陶瓷在干摩擦和水润滑条件下的磨损机理分别为微断裂磨损和陶瓷表面氧化物的水解剥落.     

锶铁氧体胶态振动注模成形技术研究

通过絮凝、振动脱水工艺处理,获得固相体积分数达50%的锶铁氧体浆料,实现了高质量锶铁氧体坯体的胶态振动注模成形.分析了工艺条件对成形过程及样品质量的影响.实验表明:胶态注模成形比凝胶注模成形需要加入更多的单体与交联剂才能得到坯体强度相当的坯体;烧成后的锶铁氧体的剩余磁感应强度为420 mT,矫顽力H_(cb)为270 kA/m,最大磁能积(BH)_(max)为34 kJ/m~3.     

Rapid fabrication of alumina-based ceramic cores for gas turbine blades by stereolithography and gelcasting

Injection moulding is accepted as one of the most important methods for shaping complex ceramic cores, which are used to form intricate internal cooling passages of gas turbine blades. But the relatively long lead time and high costs involved in the fabrication of hard tooling render it uneconomical for new products development and low-volume production. In the study, a rapid prototyping process is developed to fabricate complex-shaped alumina-based ceramic core by combining stereolithography (SL) with gelcasting. SL is utilized to fabricate an integral sacrificial resin mold, and gelcasting is utilized to form a wet ceramic core green body through polymerization of aqueous ceramic slurry. The freeze-drying process is adopted to treat the wet green body surrounded by the resin mold, the drying shrinkage is decreased, and the generation of crack can be prevented. The sintering shrinkage of ceramic core is controlled by adding magnesium oxide power and developing a novel sintering process. After the resin mold is burnt out, the complex-shaped alumina-based ceramic core is obtained.     

The effects of nanoparticle addition on SiC and AlN powder–polymer mixtures: Packing and flow behavior

The development of methods to increase sintered density and improve dimensional tolerances is a crucial issue in powder metallurgy and ceramic processing. Increasing the packing density of starting powders is one effective route to achieve high sintered density and dimensional precision. The current paper presents an in-depth study on the effect of nanoparticle addition on the powder content of SiC and AlN powder–polymer mixtures. In particular, bimodal mixtures of nanoscale and sub-micrometer particles were found to have significantly increased powder volume fraction (solids loading) in the mixtures for injection molding. This observation to increasing packing density by using nanoparticles is surprising and novel since nanoparticles are known to inherently exhibit poor packing behavior. Additionally, for a given volume fraction of powder, the bimodal μ-n suspensions had a lower viscosity at any shear rate compared to the monomodal μ-suspensions. The ability to lower the suspension viscosity by adding nanoparticles to micron-sized particles has important implications for processing of particulate suspensions by powder injection molding (PIM), extrusion, slip casting and tape casting. Samples made from bimodal powders exhibited slower polymer removal during debinding and higher densification with lower shrinkage on sintering compared to the corresponding samples made from monomodal powder mixtures.     

氧化铝陶瓷凝胶铸成型工艺的研究

对氧化铝陶瓷的凝胶铸成型工艺进行研究、研究低粘度、高固相体积分数悬浮体的制备及其固化过程．研究成型坯体干燥和成型剂脱除工艺．并通过凝胶铸成型工艺制备出形状复杂、致密的陶瓷部件。制成的AI2O3陶瓷部件组织结构均匀、尺寸精确,坯体体积密度不低于50vol％,坯体允许进行机械加工．干燥和脱除成型剂后坯体无变形开裂。     

Metal filled resin for stereolithography metal part

A new route to produce metallic parts through stereolithography is explored in this work. Stereolithography of metallic materials consists of a UV curable metallic suspension prepared with a pre-polymer acting as the binder material, a photo-initiator, metallic powder and additives. The critical material and process parameters are investigated in order to identify appropriate photosensitive metallic suspensions for stereolithography, based on their rheological and photochemical properties. Two different types of resins, unsaturated polyester and epoxy resin were considered in this study, to get a better understanding of free radical, cationic and hybrid polymerisation mechanisms, being the photo-curing reactions carried out at different light intensities. The powder used was either tungsten carbide (WC) or cobalt (Co) with different powder sizes.     

Part shrinkage anomilies from stereolithography injection mould tooling

The use of stereolithography (SL) tooling allows plastic parts to be produced by injection moulding in a very short time due to the speed of mould production. One of the supposed advantages of the process is that it provides a low volume of parts that are the same as parts that would be produced by the conventional hard tooling in a fraction of the time and cost.However, this work demonstrates different rates of polymer shrinkage are developed by parts produced by SL and conventional tooling methods. These revelations may counter the greatest advantages of the SL injection moulding tooling process as the parts do not replicate those that would be produced by conventional hard tooling.This work identifies the different shrinkage that occurs in mouldings produced by an SL mould as compared to those produced from an aluminium mould. The experiments utilise two very different types of polymers and two mould geometries, which are processed in the same manner so that the heat transfer characteristics of the moulds are isolated as the only experimental variable.The work demonstrates how the two mould materials exhibit very different rates of expansion due to the temperature profiles experienced during moulding. This expansion must be compensated for to establish the total amount of shrinkage incurred by moulded parts. The compensation is derived by a mathematical approach and by modelling using finite element analysis. Both techniques depend upon knowledge of the thermal conditions during moulding. Knowledge of these thermal conditions are obtained by real-time data acquisition and simulated by FEA modeling. The application of the findings provide knowledge of the complete shrinkage values relating to the mould material and polymer used which would enable the production of geometrically accurate parts.     

Rheological behavior of ZnO suspension with thermosensitive poly(N-isopropylacrylamide) for colloidal processing of ceramics

Novel colloidal processing using thermosensitive poly(N-isopropylacrylamide) (PNIPAM) as a coagulating agent has been developed to prepare complex-shaped ceramic components. In this work, the properties of PNIPAM aqueous solutions and the rheological behavior of ZnO suspensions with PNIPAM were investigated. The results show that the PNIPAM solutions exhibit obvious thermosensitivity and its transition temperature is around 32 °C. When the temperature is above 40 °C (T_c, the critical transition temperature of thermosensitive suspension), the 50% ZnO (volume fraction) suspension with 8 mg/mL PNIPAM has a sharp increase in viscosity and reaches up to 11.49 Pa·s at 50 °C, displaying strong elasticity. The main reasons are the increase of effective volume fraction attributed to precipitation of PNIPAM segments and the flocculation between ZnO powder particles. In addition, the maximum solid loading (volume fraction) at 20 °C is higher than that at 40 °C, which proves that the phase transition of PNIPAM can induce the flocculation of suspension.     

INJECTION MOLDED TUNGSTEN HEAVY ALLOY

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Fabrication of silica-based ceramic cores with internal lattice structures by stereolithography

Ceramic cores are widely used in investment casting, and ideal properties of cores are essential for high-quality castings. Under the circumstances requiring thick cores, solid cores are likely to encounter deformation and cracking defects due to the accumulation of shrinkage. Therefore, with the superiority of ceramic stereolithography in producing complex ceramic parts, hollow cores with lattice structures were designed and fabricated. The dimensional accuracy and properties of the green and sintered bodies were evaluated. Results show the dimensional accuracy of sintered cores is controlled within ±0.25 mm benefited from the precise green bodies. The mechanical properties are not obviously deteriorated. The bending strength reaches 11.94 MPa at room temperature and 12.87 MPa at 1,500 °C with a creep deformation of 0.345 mm. Furthermore, casting verifications prove that the hollow cores meet the requirements of investment casting. Smooth casting surfaces are obtained, at the same time, the core-removal efficiency is improved by over 3 times.

     

Multi-material stereolithography

A multi-material stereolithography (MMSL) machine was developed by retrofitting components from a commercial 3D Systems 250/50 stereolithography (SL) machine on a separate stand-alone system and adapting the components to function with additional components required for MMSL operation. The MMSL machine required construction of a new frame and the development of a new rotating vat carousel system, platform assembly, and automatic leveling system. The overall operation of the MMSL system was managed using a custom LabVIEW^® program, which included controlling a new vat leveling system and new linear and rotational stages, while the commercial SL control software (3D Systems Buildstation 4.0) was retained for controlling the laser scanning process. During MMSL construction, the sweeping process can be inhibited by previously cured layers, and thus, a deep-dip coating process without sweeping was used with low viscosity resins. Low viscosity resins were created by diluting commercial resins, including DSM Somos^® WaterShed™ 11120, ProtoTherm™ 12120, and 14120 White, with propoxylated (2) neopentyl glycol diacrylate (PNGD). Several multi-material complex parts were produced providing compelling evidence that MMSL can produce unique parts that are functional, visually illustrative, and constructed with multi-materials.     

Effects of replacing metal powder with powder space holder on metal foam produced by metal injection moulding

Porous metal has a high strength-to-weight ratio and can be produced by various methods. Powder metallurgy using a powder space holder, which is one of the metal foam fabrication techniques, can produce complex parts with a well-controlled foam structure. This work employed the metal injection moulding method with the use of a powder space holder, which was PMMA. The volume fraction of PMMA was varied from 0% to 50% to replace the metal volume fraction, while the binder volume fraction was kept constant. The results show that when more PMMA is added, the mixture of metal powder, binder and PMMA has higher wettability and became less viscous and more difficult to mix effectively and to inject. In addition, there were two competing shrinkages during sintering, which were the shrinkage due to the consolidation of the powder during sintering, which was always present, and the shrinkage of the foam structure after the power spacer was removed, which was a function of the volume fraction of PMMA. All results can be divided into two regions, which are the first region (0–35% PMMA) and the second region (35–50% PMMA). In the first region, as the volume fraction of PMMA increased, the sintered density and mechanical properties decreased, and the porosity per area decreased. For the second region, the sintered density and mechanical properties improved and the porosity per area increased as more PMMA was added. The original shape of the parts could not be retained in the second region. Microstructural observations supported these findings.