成型工艺对片式PTCR素坯及瓷片性能的影响

将注凝成型、注浆成型与轧膜成型应用于片式PTCR的制备,研究了不同成型工艺对片式 PTCR素坯及瓷片性能的影响。研究发现,用注凝成型和注浆成型工艺制备的素坯比用轧膜成型更加均匀, 其陶瓷颗粒与粘结剂分布规则。在3种成型工艺所得的瓷片中,注凝成型瓷片晶粒生长最均匀,注浆成型瓷片晶粒生长较均匀,而轧膜成型瓷片晶粒生长不均匀。注凝成型和注浆成型工艺所制备瓷片的 PTC性能稍优于轧膜成型。瓷片的耐电压性能与成型工艺有较大的依赖关系。     

水基注凝成型技术的研究进展

注凝成型是一种近净尺寸陶瓷成型技术,为制备高性能复杂形状的陶瓷制品提供了一条有效的技术途径.对陶瓷水基注凝成型技术中的悬浮体的制备、凝胶体系的选择、悬浮体的真空处理和固化、坯体和烧结体的性能特点等方面的研究进行了综述,并简要介绍了该技术的国内外应用情况,同时展望了该技术的发展趋势.     

凝胶注模成型生坯强度影响因素的研究

凝胶注模成型优于传统陶瓷成型技术的一个显著特点是坯体具有足够的机加工强度,此强度的大小与单体聚合所成聚合物的聚合度和交联度有很大关系.本实验从自由基聚合角度分析了丙烯酰胺体系注凝成型氧化铝过程中,有机单体、交联剂、引发剂、催化剂、固相含量以及添加剂聚乙二醇的加入量等固化过程的内部因素对坯体强度的影响.结果表明：在注凝成型体系中,这些物质的相对含量对所成生坯的强度有很大影响,在最佳工艺条件下,氧化铝生坯强度可达到32MPa,完全可以满足机加工要求.     

凝胶注模成型生坯强度影响因素的研究

凝胶注模成型优于传统陶瓷成型技术的一个显著特点是坯体具有足够的机加工强度，此强度的大小与单体聚合所成聚合物的聚合度和交联度有很大关系。本实验从自由基聚合角度分析了丙烯酰胺体系注凝成型碳化硼一氧化铝过程中，有机单体、交联剂、引发剂、催化剂及固相含量的内部因素对坯体强度的。影响。结果表明：在注凝成型体系中，这些物质的相对含量对所成生坯的强度有很大影响，在最佳工艺条件下，碳化硼一氧化铝生坯强度可达到32MPa，完全可以满足机加工要求。     

中间相沥青制备高密度高强度炭/石墨材料

以在不同氧化温度下制备的氧化中间相沥青为原料制备了具有不同密度的炭/石墨材料, 根据对样品物理性能和微观结构的研究得出最佳的工艺条件. 以150MPa压制的坯体经过2200℃石墨化后得到具有高密度(2.02g/cm³)、低孔率(2.03%)、大体积收缩(44.86%)、高的弯曲强度和压缩强度(70.3和123.3MPa)的样品. 该样品具有均匀致密的结构. 实验证明, 氧化中间相沥青是制备高性能炭石墨材料良好的前驱体.     

注凝成型结合先驱体转化制备C/SiC复合材料研究

采用注凝成型工艺在碳纤维编织件中引入SiC微粉,然后采用先驱体转化法进一步致密化,以缩短C/SiC复合材料的制备周期.考察了不同固相含量的SiC浆料对制备周期、密度、孔隙率及力学性能的影响.结果表明,注凝成型工艺引入的SiC微粉分布在纤维束间,当固相含量达到30%(体积分数)时,后期PIP工艺周期数比PCS/二甲苯溶液反复浸渍-裂解所用周期数缩短了1/3,但引入的SiC微粉对材料力学性能影响较大.     

注凝成型超细二氧化锆悬浮体的制备

研究了注凝成型超细ZrO2粉体(d0.5=0.199μm)悬浮体的特性及制备工艺.研究表明:采用A型分散剂(聚丙烯酸盐),分散剂用量为ZrO2粉体体积的2%～2.5%;料浆pH值为10～11;研磨时间为12h,可制备出固相体积分数达到54%的料浆悬浮体,料浆黏度为0.952 Pa*s,能够满足凝胶注成型的要求.并且可得到素坯弯曲强度达到50.09MPa的坯体,1550℃保温2h获得了结构致密、晶粒细小均匀的ZrO2陶瓷烧结体.     

高精度复杂形状碳化硅陶瓷制备工艺研究

研究了一种复杂形状碳化硅陶瓷制品制备工艺—陶瓷素坯加工工艺(GCM,Green ceramic machining).采用凝胶注成型工艺制备出简单形状碳化硅陶瓷素坯,通过数控机床对素坯陶瓷进行三维加工.研究了凝胶注模成型碳化硅陶瓷素坯强度以及显微结构,并对其加工性能(钻孔、挖槽)以及加工工艺参数进行的研究,优化了加工工艺参数并制备出了复杂形状的高精度碳化硅陶瓷制品.     

低黏结剂含量SiC素坯的选区激光烧结

Al/SiC是SiC基复合材料, 具有优异的力学性能和热学性能, 在大功率电子器件、5G基站关键冷却组件、电动汽车、高速刹车片、空间探测器操作装置等相关领域具有不可替代的作用。传统制备工艺的局限性使得近净成形的无压浸渗法成为制备Al/SiC复合材料的一种较好的方法。得到高质量的碳化硅(SiC)陶瓷素坯是熔渗技术的先决条件, 选区激光烧结技术是获得高质量陶瓷素坯的一种新方法。该方法具有快速、高效的优点, 无需模具即可成型制备大规模、复杂形状部件。本研究以热塑性酚醛树脂为黏结剂, 利用机械混合与喷雾造粒的方法制备了复合粉体, 采用选区激光烧结技术制备SiC素坯, 制备了黏结剂体积分数低至15%的样品, 并对其力学性能和微观结构进行表征。当树脂含量增大到体积分数25%时, SiC坯体的强度增量为702.1%。对于喷雾造粒粉体制备的样品而言, 喷雾干粉的多孔结构使得SiC生坯的孔隙率较高(71.18%), 导致生坯强度下降。     

注浆胶凝法陶瓷成型工艺

利用一种含钙和铝的复合盐类，使高固相含量的硅酸盐泥浆原位凝固，实现了不用多孔吸水性模具注浆成型。用这种注浆胶凝法工艺成型出各种陶瓷素坯，如陶瓷肥皂盒、陶瓷薄板、厚块、螺纹等。此工艺制备的素坯强度略低于用传统注浆成浆成型所产生的素坯的强度，而干燥收缩略大于传统的素坯。     

Microstructure and mechanical properties of hot extruded 6016 aluminum alloy/graphite composites

The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/(0-20 wt%) graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases(free graphite and in-situ formed carbides) on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide(SiC) and aluminum carbide(Al_4 C_3). The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.     

Fabrication of semi-conductive ceramics by combination of gelcasting and reduction sintering

In this study, we propose a new process to fabricate electrically semi-conductive alumina by the combination of gelcasting and reduction sintering. The process is similar to the conventional gelcasting method except for varying amounts of methacrylamide monomer dosages at 2.83, 5.50, and 8.04 wt% relative to the mass of the slurry. Correspondingly, the rheological evaluation of aqueous slurry was conducted. The resulting fluidity exhibited that monomer dosage until 8.04 wt% yielded slurry viscosity of 1628 MPA·s at shear rate of 20 s⁻¹, which was feasible for gelcasting without noticeable casting defects. The freshly gelled bodies were demolded, carefully dried, and then sintered at different schedules in nitrogen atmosphere. The reduction-sintered samples were re-sintered in air for comparative evaluation of physical property. The sintered alumina body was characterized by electrical resistance, X-ray diffraction, and scanning electron microscopy. The results showed that monomer additions and sintering schedule significantly affect in lowering electrical resistivity. The obtained lowest value was 3.6 × 10⁶ Ω-cm with 8.04 wt% monomer dosage and sintering at 1550°C with 2 h holding time. The resulting material is classified as semi-conductive, which is potential for electrostatic shielding applications. The effect of physical property and microstructure on electrical conductivity and the corresponding reaction mechanism were discussed in details.     

氧化铝陶瓷凝胶注模成型工艺的研究

探讨了陶瓷凝胶注模成型的机理和特点,研究了固相体积含量、pH值、分散剂等对制备低粘度、高固相体积含量的氧化铝陶瓷悬浮液的影响.实验结果表明,固相体积分数为55%,浆料的粘度可以满足注模的需要时坯体抗弯强度可达30MPa.控制pH值为9左右,加入8%(质量分数)的PMAA-NH4分散剂,可制得粘度低、流动性好适宜于复杂形状制品注模的陶瓷浆料.     

HEMA-TBA凝胶体系制备多孔氧化铝陶瓷

采用HEMA-TBA凝胶体系制备具有高气孔率, 高强度的多孔氧化铝陶瓷, 研究多孔氧化铝陶瓷的浆料和坯体制备工艺, 并系统研究了分散剂含量和固相体积分数对浆料粘度和悬浮稳定性的影响、干燥和单体含量对生坯性能的影响以及固相体积分数和烧结温度对烧结体微观结构的影响。结果表明: 加入柠檬酸可以使浆料粘度降低, 稳定性提高, 柠檬酸加入量达到2wt%后浆料粘度和稳定性趋于稳定; 固相体积分数的增加会导致浆料粘度和稳定性的增加; 生坯在干燥过程中的收缩比水基体系小很多, 干燥时间也相对更短; 单体含量对生坯强度影响较大, 当单体含量为25wt%时, 生坯强度较高; 通过选择不同的固相体积分数和烧结温度, 可以有效地控制烧结体的微观结构, 气孔率的变化范围在40%~65%, 同时烧结体强度也会随之发生变化, 变化范围在5.7~91.2 MPa。     

凝胶注模成形Ti6Al4V钛合金的组织和性能研究

目的 为了实现低成本、低能耗、高效率制备大尺寸复杂形状钛合金的问题,以凝胶注模技术为成形手段,制备近净成形Ti6Al4V合金,并研究其组织及性能.方法 通过溶液包覆法,在Ti6Al4V钛合金球形粉末表面包覆石蜡(PW),分析有机包覆层在凝胶注模过程中的作用机制及流变行为的影响,测定包覆前后不同粉末进行凝胶注模烧结后的组...     

粉末增塑挤压制备Al2O3/430L复合型蜂窝材料的组织与性能

为制备性能优良的Al_2O_3/430L复合型蜂窝载体材料,本文以430L不锈钢合金粉末、Al_2O_3粉末、粘结剂为原料,采用粉末增塑挤压技术挤压成形,并在1 100℃真空中烧结2 h获得Al_2O_3/430L复合型蜂窝材料.借助SEM、XRD及万能试验机,研究了添加Al_2O_3对Al_2O_3/430L复合型蜂窝材料的组织与性能的影响.研究表明:金属粉末颗粒在烧结过程中结合形成的基体组织为α-Fe(Cr),在基体晶粒间孔隙处和表面弥散分布着Al_2O_3颗粒.添加少量的Al_2O_3可提高烧结密度,制件表面光滑.随着Al_2O_3添加量增加,蜂窝材料表面负载催化涂层的能力增强;抗压强度随Al_2O_3添加量的增加先升高后降低,在Al_2O_3含量为2.5wt.%时,最大抗压强度达27 MPa.添加2.5wt.%Al_2O_3所制备的Al_2O_3/430L复合型蜂窝材料力学性能最佳、表面负载催化涂层的能力优良.     

燃料电池YSZ薄膜凝胶-流延成型的制备研究

结合流延法和凝胶法的优点,形成了水溶液丙烯酰胺体系的凝胶－流延成型方法。以固相含量为５４ｖｏｌ％的ＹＳＺ 体为浆料,利用此方法制备了厚度小、致密度高、气孔少的固体电解质ＺｒＯ２薄片,并从粉体特性、分散剂和ｐＨ值对悬浮体性能的影响、素坯及烧结体密度等多角度探讨了工艺的特点。研究表明与干压法、流延法相比,用凝胶－流延成型的薄片成型的薄片致密度高,气孔少、适合制备固体电解质ＹＳＺ薄膜。     

机械球磨制备碳微球及其吸附性能研究

分别以球墨铸铁和石墨为原料,采用机械球磨法成功制备了碳微球.采用XRD、SEM等测试手段对产物进行了形貌分析和结构表征,结果表明,所制备的碳微球产量高,并且以石墨为原料所得产物的颗粒大小均匀、分散性好.对碳微球进行了低温N_2吸附分析,结果表明,产物主要为介孔结构含有少量微孔,且具有较大的比表面积.     

激光增材制造用SiC粉末制备及成形工艺探索

为制备高强度复杂形状SiC陶瓷零件,以酚醛树脂(PF)为粘接剂,分别采用机械混合法(SPM)和搅拌蒸发法(SPC)制备两种SiC复合粉末,并对两种粉末进行了SEM电镜扫描、SLS成形、碳化和渗硅反应烧结处理.研究表明,在激光功率10 W,分层厚度0.1 mm,扫描速2 000 mm/s,扫描间距0.2 mm时,SLS坯体密度大(1.259 g/cm3),生产效率高.利用SPC粉末制得的SLS坯体内部孔隙更多,碳化和渗硅烧结后坯体密度明显增加.采用SPC粉末所制零件最终力学性能更好,更适于生产.在最优工艺条件下,制备了复杂形状的高性能SiC零件.     

A Novel Manufacturing Route for Automobile Parts through Two-Wire-Arc Thermal Spray Process

The present work deals with a novel manufacturing route that can be used to fabricate automobile sheet parts such as bonnet/bumper by metal alloy coating through two-wire-arc thermal spray (TWATS) process. Later the coating is supported with fiber through cladding process and becomes a freestanding composite coating. The coating has a metallic look and is free from oxidation. This novel manufacturing process is rapid and customized. A case study, where aluminum alloy wire was used to produce freestanding coating, was performed by response surface method optimization of the two-wire-arc spray process factors: the voltage, current, spray distance, gas pressure, and selection of mold/substrate material that was used to fabricate automobile bonnet. Initial experiments were performed on the four different substrates materials, viz., steel, aluminum, ceramic, and graphite; the graphite substrate showed some promising results and was selected to run the experimental array to optimize the process parameters. Spray distance more than 150 mm, voltage 30 V, current 250 A, and primary atomizing gas (nitrogen) pressure 100 psi (0.689 MPa) may be used. The freestanding aluminum coating was evaluated analyzing its performance, in terms of desirable microstructure and mechanical properties.