自成核行为在CF/PPS复合材料中的差异性与普适性

以半结晶高分子为基体的碳纤维增强热塑性复合材料,其基体的结晶行为将受到碳纤维表面性质与热历史的共同影响。当这种材料在经历反复加热冷却的热循环过程时,基体会产生自成核行为,其结晶过程变得更加复杂。通过三种T300级碳纤维分别制备了碳纤维增强聚苯硫醚(CF/PPS)复合材料,并探究了二次熔融温度与CF/PPS复合材料结晶行为的关系,揭示了不同碳纤维表面性质对CF/PPS复合材料自成核行为的影响。在此基础上阐明了CF/PPS复合材料基体自成核与CF异相成核的竞争关系。最后,通过冲压成型制得具有自成核行为的CF/PPS复合材料角片,验证了自成核对于CF/PPS复合材料二次热成型技术的有效性与重要性。

Phase-Field Simulation of Sintering Process:A Review

Sintering,a well-established technique in powder metallurgy,plays a critical role in the processing of high melting point materials.A comprehensive understanding of structural changes during the sintering process is essential for effective product assessment.The phase-field method stands out for its unique ability to simulate these structural transformations.Despite its widespread application,there is a notable absence of literature reviews focused on its usage in sintering simulations.Therefore,this paper addresses this gap by reviewing the latest advancements in phase-field sintering models,covering approaches based on energy,grand potential,and entropy increase.The characteristics of various models are extensively discussed,with a specific emphasis on energy-based models incorporating considerations such as interface energy anisotropy,tensor-form diffusion mechanisms,and various forms of rigid particle motion during sintering.Furthermore,the paper offers a concise summary of phase-field sintering models that integrate with other physical fields,including stress/strain fields,viscous flow,temperature field,and external electric fields.In conclusion,the paper provides a succinct overview of the entire content and delineates potential avenues for future research.

Spark Plasma Sintering of Boron Carbide Using Ti_(3)SiC_(2) as a Sintering Additive

Boron carbide has unique properties for wide application possibilities;however,poor sinterability limits its applications.One approach to overcome this limitation is the addition of secondary phases into boron carbide.Boron carbide based composite ceramics are produced by the direct addition of secondary phases into the structure or via reactive sintering using a sintering additive.The present study investigated the effect of Ti_(3)SiC_(2) addition to boron carbide by reactive spark plasma sintering in the range of 1700-1900℃.Ti_(3)SiC_(2) phase decomposed at high temperatures and reacted with B4C to form secondary phases of TiB2 and SiC.The results demonstrated that the increase of Ti_(3)SiC_(2) addition(up to 15 vol%)effectively promoted the densification of B4C and yielded higher hardness.However,as the amount of Ti_(3)SiC_(2) increased further,the formation of microstructural inhomogeneity and agglomeration of secondary phases caused a decrease in hardness.

Effect of Sintering Temperature on the Microstructure and Mechanical Properties of Nanocrystalline Cemented Carbide

WC-Co nanocrystalline nitrogen-containing cemented carbides were prepared by vacuum sintering and low pressure sintering.The sintering processes of Cr_(2)(C,N)doped nano WC-Co powders were studied by using thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).The effect of sintering temperature on the microstructure and mechanical properties of nanocrystalline cemented carbide was studied by scanning electron microscope(SEM),high resolution transmission electron microscope(HRTEM)and mechanical property test.The results showed that the nano WC grains began to grow in the solid phase sintering stage.A high-performance nano-nitrogen-containing cemented carbide with uniform microstructure and good interfacial bonding can be obtained by increasing the sintering temperature to 1380℃.It has a transverse rupture strength(TRS)of 5057 MPa and a hardness of 1956 HV30.

Spark Plasma Sintering of Mg-based Alloys:Microstructure,Mechanical Properties,Corrosion Behavior,and Tribological Performance

Within the past ten years,spark plasma sintering(SPS)has become an increasingly popular process for Mg manufacturing.In the SPS process,interparticle diffusion of compressed particles is rapidly achieved due to the concept of Joule heating.Compared to traditional and additive manufacturing(AM)techniques,SPS gives unique control of the structural and microstructural features of Mg components.By doing so,their mechanical,tribological,and corrosion properties can be tailored.Although great advancements in this field have been made,these pieces of knowledge are scattered and have not been contextualized into a single work.The motivation of this work is to address this scientific gap and to provide a groundwork for understanding the basics of SPS manufacturing for Mg.To do so,the existing body of SPS Mg literature was first surveyed,with a focus on their structural formation and degradation mechanisms.It was found that successful Mg SPS fabrication highly depended on the processing temperature,particle size,and particle crystallinity.The addition of metal and ceramic composites also affected their microstructural features due to the Zener pinning effect.In degradative environments,their performance depends on their structural features and whether they have secondary phased composites.In industrial applications,SPS'd Mg was found to have great potential in biomedical,hydrogen storage,battery,automotive,and recycling sectors.The prospects to advance the field include using Mg as a doping agent for crystallite size refinement and using bulk metallic Mg-based glass powders for amorphous SPS components.Despite these findings,the interactions of multi-composites on the processing-structure-property relationships of SPS Mg is not well understood.In total,this work will provide a useful direction in the SPS field and serve as a milestone for future Mg-based SPS manufacturing.

Fabrication of YAG:Ce^(3+) and YAG:Ce^(3+),Sc^(3+) Phosphors by Spark Plasma Sintering Technique

In this study,a single-doped phosphors yttrium aluminum garnet(Y_(3)Al_(5)O_(12),YAG):Ce^(3+),single-doped YAG:Sc^(3+),and double-doped phosphors YAG:Ce^(3+),Sc^(3+) were prepared by spark plasma sintering(SPS)(lower than 1 200℃).The characteristics of synthesized phosphors were determined using scanning electron microscopy(SEM),X-ray diffraction(XRD),and fluorescence spectroscopy.During SPS,the lattice structure of YAG was maintained by the added Ce^(3+) and Sc^(3+).The emission wavelength of YAG:Ce^(3+) prepared from SPS(425-700 nm) was wider compared to that of YAG:Ce^(3+) prepared from high-temperature solid-state reaction(HSSR)(500-700 nm).The incorporation of low-dose Sc^(3+) in YAG:Ce^(3+) moved the emission peak towards the short wavelength.

Spark plasma sintering of tungsten-based WTaVCr refractory high entropy alloys for nuclear fusion applications

W-based WTaVCr refractory high entropy alloys (RHEA) may be novel and promising candidate materials for plasma facing components in the first wall and diverter in fusion reactors. This alloy has been developed by a powder metallurgy process combining mechanical alloying and spark plasma sintering (SPS). The SPSed samples contained two phases, in which the matrix is RHEA with a body-centered cubic structure, while the oxide phase was most likely Ta2VO6through a combined analysis of X-ray diffraction (XRD),energy-dispersive spectroscopy (EDS), and selected area electron diffraction (SAED). The higher oxygen affinity of Ta and V may explain the preferential formation of their oxide phases based on thermodynamic calculations. Electron backscatter diffraction (EBSD) revealed an average grain size of 6.2μm. WTaVCr RHEA showed a peak compressive strength of 2997 MPa at room temperature and much higher micro-and nano-hardness than W and other W-based RHEAs in the literature. Their high Rockwell hardness can be retained to at least 1000°C.

重庆沃尔夫化工推出超级PPS材料为新能源电机行业保驾护航

重庆沃尔夫化工有限公司利用独特的PPS树脂处理技术和改性技术,在三电行业隆重推出耐高温老化电气性能不衰减、超级防水的PPS材料,经过200℃老化2000 h后,绝缘电阻继续保持在同一数量级,CTI值继续保持在老化前水平。在水泡15 d后,绝缘电阻继续保持在泡水前水平。

Research on Adaptive Cluster Sampling Method Based on PPS

This paper introduces the principle of PPS-based adaptive cluster sampling method and its modified HH estimator and HT estimator calculation method. It compares PPS-based adaptive cluster sampling method with SRS sampling and SRS-based adaptive group. The difference between the group sampling and the advantages and scope of the PPS adaptive cluster sampling method are analyzed. According to the case analysis, the relevant conclusions are drawn: 1) The adaptive cluster sampling method is more accurate than the SRS sampling;2) SRS adaptive The HT estimator of the cluster sampling is more stable than the HH estimator;3) The two estimators of the PPS adaptive cluster sampling method have little difference in the estimation of the population mean, but the HT estimator variance is smaller and more suitable;4) PPS The HH estimator of adaptive cluster sampling is the same as the HH estimator of SRS adaptive cluster sampling, but the variance is larger and unstable.

高温气相环境对PTFE/PPS复合膜性能影响

聚四氟乙烯/聚苯硫醚(PTFE/PPS)复合膜是除尘领域运用最广泛的复合膜之一,其使用寿命受烟气参数影响显著.本研究针对PTFE/PPS复合膜的实际应用条件,通过高温气相腐蚀对PTFE/PPS复合膜进行抗老化性能测试,在120~240℃温度范围内,以空气为气氛,研究了氧存在条件对PTFE/PPS复合膜的耐老化性能影响;基于腐蚀气体(SO_(2))浓度、腐蚀温度与时间,建立了膜材料拉伸强度的响应曲面模型.研究结果表明,氧气使复合膜中的PPS支撑体产生氧化交联反应使其纬向断裂强力有所上升,200℃老化48 h后达到最大值2132.2 N;由响应面可知,增加温度与SO_(2)浓度对PTFE/PPS复合膜的断裂拉伸性能的衰减影响显著,当温度从180℃增加到240℃时,其经向断裂强力衰减至初始值的90.97%;当SO_(2)浓度由2096 mg/m^(3)增加至2620 mg/m^(3)时,经向断裂强力衰减至初始值的98.12%.该工作为复合膜在烟气净化中的应用条件优化提供了依据.

酚酞型聚芳醚酮与硅烷偶联剂协同改性CF/PPS复合材料

本文使用不同浓度的KH570溶液和0.5wt%的PEK-C溶液依次对碳纤维进行改性处理,并通过模压成型制备了CF/PPS复合材料,使用X射线光电子能谱仪(XPS)、扫描电子显微镜(SEM)、X射线衍射仪(XRD)、万能材料试验机等手段表征改性后的CF/PPS复合材料。结果表明,使用2wt%的KH570溶液和0.5wt%的PEK-C溶液依次处理碳纤维后,复合材料的界面性能和弯曲性能大幅提升,相较于未经改性处理的CF/PPS复合材料,其弯曲强度由709 MPa提高至953 MPa,提升约34.4%,ILSS则由23.8 MPa提高至53.3 MPa,提升约123.9%。

老化对PTFE/PPS复合涂层的疏水和防结冰性能的影响

目的飞机表面涂层在服役过程中受到高温、太阳光辐射作用,容易引起微观结构的破坏,失去原有的性能。本文探究了老化对PTFE/PPS复合涂层疏水、防结冰性能的影响。方法利用一步喷涂法在TC4基体上制备出PTFE/PPS复合涂层,使用SEM和三维形貌仪进行表面形貌分析,利用傅里叶红外光谱仪以及XPS分析涂层元素组成,在对制得的PTFE/PPS复合涂层进行高温热老化(24、48、96 h)以及太阳辐射光老化(24、48、96 h)实验后,对其进行疏水防结冰性能测试。结果原始的PTFE/PPS复合涂层和经过24、48、72高温热老化后PTFE/PPS复合涂层的表面粗糙度分别为8.075μm、5.383μm、4.583μm、5.466μm,静态水接触角由139.70°降至132.36°、131.13°、130.36°,结冰时间由最初的346 s缩短至326 s、309 s、294 s,冰晶黏附力由最初的8.65 N增加至8.90 N、9.15 N、9.65 N。经过24、48、72 h太阳辐射光老化后,PTFE/PPS复合涂层的表面粗糙度分别为10.549μm、10.974μm、9.969μm,静态水接触角由139.70°降至135.83°、133.85°、129.97°,结冰时间由最初的346 s缩短为317 s、269 s、242 s,冰晶黏附力由最初的8.65 N增加至9.05 N、9.15 N、9.40 N。结论热老化和光老化虽然会使PTFE/PPS复合涂层的疏水、防结冰性能有所下降,但与基体相比仍能保持良好的疏水、防结冰性能。

Anti-sintering behavior and combustion process of aluminum nano particles coated with PTFE:A molecular dynamics study

The characteristic of easy sintering of aluminum nanoparticle(ANP)limits its application in solid propellants.Coating ANP with fluoropolymer could effectively improve its combustion performance.To find out how the coating layer inhibits sintering and promotes complete combustion of particles from an atomic view,a comparative study has been done for bare ANP and PTFE coated ANP by using reactive molecular dynamics simulations.The sintering process is quantified by shrinkage ratio and gyration radius.Our results show that,at the same heating rate and combustion temperatures,bare ANPs are sintered together after the temperature exceeds the melting point of aluminum but the decomposition of PTFE coating layer pushes particles away and increases reaction surface area by producing small Al-F clusters.The sintering of ANPs which are heated in PTFE is alleviated compared with particles heated in oxygen,but particles still sinter together due to the lack of intimate contact between PTFE and alumina surface.The effect of temperature on the combustion of PTFE coated ANPs is also studied from 1000 to3500 K.The number density analysis shows the particles will not be sintered at any temperature.Aluminum fluoride prefers diffusing to the external space and the remained particles are mainly composed of Al,C and O.Fast ignition simulations are performed by adopting micro canonical ensemble.With the expansion of aluminum core and the melting of alumina shell,bare ANPs are sintered into a liquid particle directly.For PTFE coated ANPs,the volatilization of gaseous aluminum fluoride products continually endows particles opposite momentum.

Influences of oxide content and sintering temperature on microstructures and mechanical properties of intragranular-oxide strengthened iron alloys prepared by spark plasma sintering

How to increase strength without sacrificing ductility has been developed as a key goal in the manufacture of high-performance metals or alloys. Herein, the double-nanophase intragranular yttrium oxide dispersion strengthened iron alloy with high strength and appreciable ductility was fabricated by solution combustion route and subsequent spark plasma sintering, and the influences of yttrium oxide content and sintering temperature on microstructures and mechanical properties were investigated. The results show at the same sintering temperature,with the increase of yttrium oxide content, the relative density of the sintered alloy decreases and the strength increases. For Fe–2wt%Y_(2)O_(3)alloy, as the sintering temperature increases gradually, the compressive strength decreases, while the strain-to-failure increases. The Fe–2wt%Y_(2)O_(3)alloy with 15.5 nm Y_(2)O_(3)particles uniformly distributed into the 147.5 nm iron grain interior sintered at 650℃ presents a high ultimate compressive strength of 1.86 GPa and large strain-to-failure of 29%. The grain boundary strengthening and intragranular second-phase particle dispersion strengthening are the main dominant mechanisms to enhance the mechanical properties of the alloy.

Evaluation of the Air Leakage Flowrate in Sintering Processes

Iron ore sintering is a pre-treatment technology by which orefines are converted into porous and permeable sin-ters,which are the used in blast furnaces.This process can be adversely affected by air leakage phenomena of various types.As experimental measurements are relatively difficult and often scarcely reliable,here a theoretical model based on typicalfluid-dynamic concepts and relationships is elaborated.Through the analysis of two extreme cases,namely,those in which leakage is due to a small hole or a full rupture,a generalized hole-bed mod-el is introduced,which for thefirst time also includes a complete bed permeability equation and can deal with different leakage position conditions.The results show that the model can evaluate the influence of leakage on the system at one time and be used to calculate theflowrate and pressure drop.Notably,the obtained results are within a 15%deviation with respect to available experiment values,used for comparison.

Effect of sintering temperature on microstructure and properties of 3D printing polysilazane reinforced Al_(2)O_(3)core

Ceramic cores are the key intermediate components of hollow blades for aero-engine.Conventional processes,such as hot-press molding and gel film casting,face difficulties in fabricating complex-structured ceramic cores due to the complexity of moulds and long process cycles.Stereolithography 3D printing provides a new idea for the fabrication of complex-structured ceramic cores.The effect of sintering temperature on open porosity,bulk density,weight loss rate,shrinkage rate,flexural strength and microstructure of the Al_(2)O_(3)-based ceramic core doped with 10vol.%polysilazane(PSZ)was studied.The sintering mechanism of PSZ-reinforced ceramic cores was analyzed.Results show that the optimum sintering temperature of PSZ-reinforced ceramic cores is 1,450°C.At this temperature,the open porosity of the ceramic core is 36.60%,bulk density is 2.33 g·cm^(-3),weight loss rate is 22.11%,shrinkage rate along the X,Y,Z directions is 5.72%,5.01%,9.61%,respectively;the flexural strength is 28.794 MPa at 25°C and 13.649 MPa at 1,500°C.Properties of 3D printing PSZ-reinforced ceramic cores can meet the casting requirement of superalloy hollow blades,which is expected to promote the industrial application of 3D printing complex structure ceramic cores.

Preparation of coated sand for selective laser sintering and optimization of baking process of sand moulds

A cold method was used to prepare coated sand for application in the selective laser sintering(SLS)process.Tensile strength,loss on ignition,gas evolution,and accuracy of the SLS samples were tested and analyzed,and the baking process was thoroughly investigated.Compared with coated sand prepared by the hot method,the cold method yields a more uniform and complete resin film on the sand's surface,resulting in enhanced tensile strength and accuracy.Additionally,the cold method requires a lower binder content to meet the same strength requirements,thereby minimizing gas evolution,reducing porosity defects,and ultimately improving casting quality.The coated sand samples prepared through the cold method exhibit superior accuracy,with a size error of within±0.4 mm.In contrast,the coated sand samples prepared by the hot method display a lower accuracy,with an average negative error of 2.1993 mm.The highest tensile strength could be attained by controlling the baking temperature within a suitable range(180-190°C),which can effectively reduce the generation of gas,thus contributing to improved overall performance.

Effect of steam spraying on a sintering bed on sinter quality and the emission of flue gas pollutants

The technology for spraying a sintering bed and thus improving sinter quality indicators while reducing the emission of flue gas pollutants has recently become an important research topic.The impacts on sinter quality and emissions when spraying the sintering surface with different amounts and flow rates of steam were investigated in this study.The sinter quality indicators were most effectively improved by spraying 180 g of steam flow continuously at a rate of 0.02 m^(3)/min for 15 min after ignition for 8 min.The optimal effect on emission reduction was obtained by spraying 90 g of steam flow continuously at a rate of 0.01 m^(3)/min for 15 min after ignition for 8 min.

LiCoO_(2) sintering aid towards cathode-interface-enhanced garnet electrolytes

Garnet-type Li_7La_(3)Zr_(2)O_(12)(LLZO) has high ionic conductivity and good compatibility with lithium metal.High-temperature processing has been proven an effective method to decrease the interface resistance of cathodeILLZO.However,its application is still hindered by the interlayer co-diffusion with the cathode and high sintering temperature(>1200℃).In this work,a new garnet-type composite solid-state electrolyte(SSE) Li_(6.54)La_(2.96)Ba_(0.04)Zr_(1.5)Nb_(0.5)O_(12)-LiCoO_(2)(LLBZNO-LCO) is firstly proposed to improve the chemical stability and electrochemical properties of garnet with high-temperature processing.Small doses of LCO(3%) can significantly decrease the LCOISSE interface resistance from 121.2 to 10.1 Ω cm~2,while the sintering temperature of garnet-type LLBZNO decreases from 1230 to 1000℃.The all-solid-state battery based on the sintered LLBZNO-LCO SSE exhibits excellent cycling stability.Our approach achieves an enhanced LCOISSE interface and an improved sintering activity of garnet SSE,which provides a new strategy for optimizing the comprehensive performance of garnet SSE.

Sintering Densification of Boron Carbide Materials and Their Research Progress

Boron carbide(B_(4)C)has excellent high-temperature oxidation resistance,high hardness,low relative density,high melting point and excellent abrasive resistance,which is widely used in fields such as refractories,wear-resistant materials and lightweight protective materials.The research progress and application of B_(4)C materials in China and overseas in recent years were summarized.The influences of sintering processes(pressureless sintering,hot-pressing sintering,hot isostatic pressing sintering,spark plasma sintering and microwave sintering)and sintering additives(simple substances,oxides and carbides)on the B_(4)C densification were analyzed.The development of B_(4)C materials was prospected.