Laser cladding in-situ carbide particle reinforced Fe-based composite coatings with rare earth oxide addition

Particulate reinforced metal matrix composite(PR-MMC) has excellent properties such as good wear resistance,corrosion resistance and high temperature properties.Laser cladding is usually used to form PR-MMC on metal surface with various volume fractions of ceramic particles.Recent literatures showed that laser melting of powder mixture containing carbon and carbide-forming elements,was favorable for the formation of in-situ synthesized carbide particles.In this paper,rare earth oxide(RE2O3) was added into t...

Fabrication and Properties of Three-dimensional Braided Carbon Fiber Reinforced SiO2-rich Mullite Composites

In order to enhance the fracture toughness of mullite, three-dimensional braided carbon fiber reinforced mullite(C/mullite) composites were prepared using the Al2O3-SiO2 sol with a high solid content as raw material. Mullitization behavior of the sol was characterized. Then, the microstructure, mechanical properties and oxidation resistance of C/mullite composites were investigated. It is found that the SiO2-rich mullite with desirable sintering shrinkage can be synthesized at 1 300 ℃ from the sol with an Al2O3/SiO2 mass ratio of 1:1. The C/mullite composites with a total porosity of 21.5% were fabricated by repeating 18 cycles of vacuum impregnation-drying-heat treatment, showing a flexural strength of 234.5 MPa and a fracture toughness of 13.1 MPa·m1/2. Since carbon fibers were protected by compact matrix, the C/mullite composites show favorable oxidation resistance during 1 200 ℃-1 600 ℃ even if an open porosity of 10.3% was detected.

Effects of SiC interfacial coating on mechanical properties of carbon fiber needled felt reinforced sol-derived Al2O3 composites

3D carbon fiber needled felt and polycarbosilane-derived SiC coating were selected as reinforcement and interfacial coating,respectively,and the sol-impregnation-drying-heating(SIDH)route was used to fabricate C/Al2O3 composites.The effects of Si C interfacial coating on the mechanical properties,oxidation resistance and thermal shock resistance of C/Al2O3 composites were investigated.It is found that the fracture toughness of C/Al2O3 composites was remarkably superior to that of monolithic Al2O3 ceramics.The introduction of SiC interfacial coating obviously improved the strengths of C/Al2O3 composites although the fracture work diminished to some extent.Owing to the tight bonding between SiC coating and carbon fiber,the C/SiC/Al2O3 composites showed much better oxidation and thermal shock resistance over C/Al2O3 composites under static air.

Preparation of three-dimensional braided carbon fiber reinforced mullite composites from a sol with high solid content

To prepare the three-dimensional braided carbon fiber reinforced mullite （3D C/mullite） composites, an Al2O3-SiO2 solwith a solid content of 20% （mass fraction） and an Al2O3/SiO2 mass ratio of 2：1 was selected as the raw material. Characteristics andmullitization of the sol were analyzed throughly. It is found that the formation of mullite is basically completed at 1300℃ and thegel powders exhibit favorable sintering shrinkage. The 3D C/mullite composites without interfacial coating were fabricated throughthe route of vacuum impregnation-drying-heat treatment. Satisfied mechanical properties with a flexural strength of 241.2 MPa anda fracture toughness of 10.9 MPa·m1/2are obtained although the total porosity reaches 26.0%. Oxidation resistances of the compositesat 1200, 1400 and 1600 ℃ were investigated. Due to the further densification of matrix, the 3D C/mullite composites show tiny massloss and their mechanical properties are well retained after oxidation at 1600 ℃ for 30 min.

Study on Diffusion Welding Parameters of Particle reinforced Aluminium Matrix Composite Al_2O_(3p) /6061Al

Effects of diffusion welding process parameters on strength of welded joint based on particle reinforced aluminium matrix composite Al 2O 3p /6061Al have been studied through comparing with aluminium matrix alloy. The mechanism for loss of joint strength has been analyzed. It should be pointed out that key processing parameters affecting the strength of joint was welding temperature. The high quality joint can be successfully obtained with appropriate diffusion welding parameters.

Preparation of SiC_p/Al_2O_3-Al Composites by Directed Metal Oxidation

SiCp/Al2O3-Al composites were synthesized by means of direct metal oxidation method. The composition and microstructures of the composites were investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） and metallurgical microscope. The effects of technical parameters on the properties of the product were analyzed. The results indicate that the composite possesses a dense microstructure, composed of three interpenetrated phases. Of them, SiO2 layer prohibits the powdering of the composites; Mg promotes the wetting and infiltration of the system and Si restricts the interfacial reaction while improving the wetting ability between reinforcement and matrix.

Oxidation behaviors of carbon fiber reinforced multilayer SiC–Si_(3)N_(4) matrix composites

Oxidation behaviors of carbon fiber reinforced SiC matrix composites(C/SiC)are one of the most noteworthy properties.For C/SiC,the oxidation behavior was controlled by matrix microcracks caused by the mismatch of coefficients of thermal expansion(CTEs)and elastic modulus between carbon fiber and SiC matrix.In order to improve the oxidation resistance,multilayer SiC–Si_(3)N_(4) matrices were fabricated by chemical vapor infiltration(CVI)to alleviate the above two kinds of mismatch and change the local stress distribution.For the oxidation of C/SiC with multilayer matrices,matrix microcracks would be deflected at the transition layer between different layers of multilayer SiC–Si_(3)N_(4) matrix to lengthen the oxygen diffusion channels,thereby improving the oxidation resistance of C/SiC,especially at 800 and 1000℃.The strength retention ratio was increased from 61.9%(C/SiC–SiC/SiC)to 75.7%(C/SiC–Si_(3)N_(4)/SiC/SiC)and 67.8%(C/SiC–SiC/Si_(3)N_(4)/SiC)after oxidation at 800℃for 10 h.

Tensile Strength and Oxide Analysis of Carbon Steel in Concrete Exposed in Atmospheric Environment for 53 Years

The tensile strength of a corroded rebar in a 53-year-old concrete structure was studied. The microstructure of the metallic substrate, the fracture surface, and the corrosion product layers were investigated. Metallographic observation results showed that the carbon steel was constituted of ferrite and some pearlite. The tensile test results indicated that the corroded rebar presented low strength and elongation. In addition, the fracture surface of the rebar in the tensile test displayed dimple fracture behavior. The Raman spectroscopy results indicated that corrosion products at the general corrosion zone were obviously different from those at the localized corrosion zone. The rust layer at the general corrosion zone was composed of goethite （α-FeOOH）, magnetite （Fe304）, and hematite （α-Fe203）, while that of the pitting zone was made of feroxyhyte （δ-FeOOH）, goethite （α-FeOOH）, and hematite （α-Fe203）. However, the general tendencies that the corrosion products were constituted of a mix of oxides and hydroxides, the oxides mainly existed in the internal part and the hydroxides more presented in the external layer were observed.

氧化石墨烯对天然水硬性石灰水化及力学性能的影响

石质文物是一类重要的文化遗产,然而裂隙会导致其产生失稳、渗水、风化等病害,因此,开发一种合适的灌浆材料用于石质文物裂隙修复具有重要意义。本文将氧化石墨烯(GO)掺入天然水硬性石灰(NHL2)制备灌浆材料,采用SEM、TG、XRD和FT-IR等测试研究了GO掺量对NHL2水化进程及水化产物的影响,通过力学性能测试和模拟灌浆试验评价了该材料用于石质文物灌浆加固的可行性。结果表明:添加GO可加速NHL2的水化进程,促进规整致密的花状聚集态水化产物的形成;当GO掺量为0.05%(质量分数)时,试样的水化产物含量最多,力学性能最好,28 d抗压强度和抗折强度分别达2.83和1.63 MPa,相比空白试样分别提高了19.91%和23.40%。此外,灌浆材料与砂岩之间具有优异的黏结强度,两者界面结合紧密,兼容性良好。本研究为石质文物的裂隙灌浆加固提供了参考。

铝酸盐体系中氧化时间对碳化硅颗粒增强铝基复合材料微弧氧化膜层的影响

[目的]探究氧化时间对碳化硅颗粒增强铝基(SiC_(p)/Al)复合材料微弧氧化膜层的影响。[方法]选用铝酸盐体系作为电解液,对SiC_(p)/Al复合材料进行微弧氧化处理,分析氧化时间对膜层组织结构、物相、厚度、粗糙度、结合力、电绝缘性及耐蚀性的影响。[结果]随着氧化时间延长,膜层逐渐变得连续均匀,厚度增加。若氧化时间过长,膜层会出现层叠现象,形成大尺寸微孔及裂纹,且生长速率越来越低。膜层结合力随氧化时间延长先增大后减小,在60 min时最大,达到39.85 N。氧化时间为10 min时,膜层的电绝缘性及耐蚀性最优,100 V和500 V电压下的绝缘电阻分别达到3.11×10^(12)Ω和1.41×10^(12)Ω,腐蚀电位为-0.6298 V,腐蚀电流密度为1.332×10^(-7)A/cm^(2)。[结论]SiC_(p)/Al复合材料表面微弧氧化膜层的连续性、均匀性及生长速率均与氧化时间有关。需选择合适的氧化时间,才能制备出连续、均匀且综合性能优异的膜层。

电压对15%SiC_(p)/2009铝基复合材料微弧放电析出气体成分的影响

在硅酸盐溶液中,对15%SiC_(p)/2009铝基复合材料进行不同电压下的微弧氧化试验。通过分析微弧放电过程中复合材料析出气体的组成,评估电压对阳极析出气体成分的影响,并阐释其产生机制。结果表明:不同电压下阳极析出的气体均由H_(2)、O_(2)及少量CO组成,不同于传统电化学理论认为的阳极析出氧气。在360~440 V范围内,随着电压的升高,放电火花强度增大,微弧氧化膜生长速率加快,H_(2)含量随之增加,O_(2)含量相应降低;电压超过440 V后,H_(2)含量约为80%(体积分数),O_(2)含量约为20%,两者含量保持稳定。阳极火花放电区水热分解释放大量H_(2)和O_(2),且放电越剧烈,水分解量越多。放电区中铝和水氧化反应及高能电子轰击电离水分子也是过量H_(2)析出的重要原因。此外,SiC增强体参与成膜过程,并在放电区高温环境中被氧化,生成了少量的CO气体。

60%SiCp/2009铝基复合材料表面等离子体电解氧化膜的生长和表征

在硅酸盐溶液中采用等离子体电解氧化技术在60%SiCP(体积分数)/2009铝基复合材料表面制备陶瓷膜。研究氧化膜的显微组织、成分、润湿性及其耐腐蚀性能,探讨SiC颗粒表面火花放电的产生机理。结果表明,来自硅酸盐溶液的不溶性化合物(SiO_(2))使SiC颗粒表面产生火花放电,Al-Si-O化合物中的缺陷为SiC颗粒表面放电电流的传导提供优先路径。1200s时铝基复合材料表面形成5.5μm厚的均匀膜层,膜层的表面自由能在40s时达到最大值37.10 m J/cm^(2),并在1200 s时下降到25.95 m J/cm^(2)。此外,等离子体电解氧化处理可以显著提高复合材料的耐蚀性。

热法增强型PVDF/GO中空纤维膜结构构筑与机理

目前,膜生物反应器(MBR)用中空纤维膜量大,制备过程中使用溶剂易造成二次污染,本文采用绿色稀释剂热致相分离(TIPS)法与纤维增强联用技术制备了大通量、高强度氧化石墨烯(GO)掺杂编织管增强型聚偏氟乙烯(PVDF)中空纤维膜。GO表面具有含丰富氧官能团可明显改善PVDF中空纤维膜渗透通量与亲水性(抗污染性)。结果表明:纤维增强技术可使中空纤维膜断裂强度223.75MPa,随GO含量增加,增强型PVDF中空纤维膜水接触角值从102.04°降低至89.71°,纯水通量从920.74L/(m_(2)·h)增至1417.45L/(m_(2)·h)。经实验用MBR小试装备测试膜活性污泥过滤表明,其截留率大于99.50%,稳定运行后截留率仍大于98%。因此,本文全流程绿色制备的增强型PVDF中空纤维膜对替代目前市场二次污染中空纤维膜可提供科学依据与技术支撑。

补强剂和硫化剂对硅橡胶胶料耐热氧老化性能的影响

以甲基乙烯基硅橡胶(以下简称硅橡胶)为主体材料,气相法白炭黑或沉淀法白炭黑为补强剂,硫化剂双25或铂金硫化剂为硫化剂,研究补强剂和硫化剂对硅橡胶胶料耐热氧老化性能的影响。结果表明:补强剂对硅橡胶胶料的耐热氧老化性能的影响更显著。随着老化时间的延长,气相法白炭黑补强的硅橡胶胶料的交联密度呈现增大的趋势,硬度增大,拉伸强度先增大后减小,拉断伸长率减小;沉淀法白炭黑补强的硅橡胶胶料的交联密度先减小后增大,硬度、拉伸强度、拉断伸长率均呈减小趋势,综合而言,沉淀法白炭黑补强的硅橡胶胶料的耐热氧老化性能略优。使用不同硫化剂的硅橡胶胶料热氧老化前的性能相当,热氧老化后,与使用硫化剂双25的硅橡胶胶料相比,使用铂金硫化剂的硅橡胶胶料的交联密度和硬度略小,拉断伸长率增大,耐热氧老化性能略优。

A Novel Multiscale Reinforcement by In-Situ Growing Carbon Nanotubes on Graphene Oxide Grafted Carbon Fibers and Its Reinforced Carbon/Carbon Composites with Improved Tensile Properties

In-situ growing carbon nanotubes （CNTs） directly on carbon fibers （CFs） always lead to a degraded tensile strength of CFs and then a poor fiber-dominated mechanical property of carbon/carbon composites （C/ Cs）. To solve this issue, here, a novel carbon fiber-based multiscale reinforcement is reported. To synthesize it, carbon fibers （CFs） have been first grafted by graphene oxide （GO）, and then carbon nanotubes （CNTs） have been in-situ grown on GO-grafted CFs by catalytic chemical vapor deposition. Characterizations on this novel reinforcement show that GO grafting cannot only nondestructively improve the surface chemical activity of CFs but also protect CFs against the high-temperature corrosion of metal catalyst during CNT growth, which maintains their tensile properties. Tensile property tests for unidirectional C/Cs with different preforms show that this novel reinforcement can endow C/C with improved tensile properties, 32% and 87% higher than that of pure C/C and C/C only doped with in-situ grown CNTs. This work would open up a possibility to fabricate multiscale C/Cs with excellent global performance.

高性能TEMPO功能化木粉-聚乙烯醇/锂铝水滑石复合材料的制备及性能

【目的】探究聚乙烯醇/锂铝水滑石(PVA/LDH)分散液对巴沙木加工剩余物理化性能的影响,为构建高性能木质复合材料提供理论依据,实现木材加工剩余物的高值化利用。【方法】受天然贝壳“砖-泥”有序结构启发,以巴沙木加工剩余物(木粉)为主要原料,经脱木素和氧化改性,获得2,2,6,6-四甲基哌啶-1-氧自由基(TEMPO)功能化改性木粉(T-WP),向其中加入不同比例PVA/LDH分散液,通过真空抽滤自组装过程将无机纳米片水滑石插层,构建天然有机聚合物与无机纳米片复合的高性能新型木质层状复合材料,基于FTIR、XPS、Zeta电位、力学性能等测试与分析,探究各组分间的相互作用及机械性能协同增强机制。【结果】1)木粉粒径100目时,纯T-WP薄膜的力学拉伸强度和韧性最大,分别为(225.25±0.82)MPa和(5.18±0.36)MJ·m^(-3)。2)PVA/LDH纳米片体系在T-WP上成功插层,并与T-WP分子链上的含氧官能团形成氢键、静电相互作用以及共价交联作用。3)对不同PVA/LDH添加量的T-WP-PVA/LDH复合材料进行力学性能分析,PVA/LDH添加量为20 wt%时,T-WP-PVA/LDH复合材料的拉伸强度和杨氏模量最大,分别为(287.29±4.91)MPa和(14.21±2.60)GPa,是纯T-WP的1.28和2.40倍。4)在相对湿度90%、温度25℃条件下放置16 h,T-WP-PVA/LDH复合材料的吸湿率为45.43%,力学拉伸强度为105.40 MPa;在湿润土壤中,T-WP-PVA/LDH复合材料表现出较好的可生物降解特性。【结论】T-WP-PVA/LDH仿生层状复合材料中,T-WP分子链上的活性含氧基团与PVA/LDH体系形成氢键、静电相互作用以及Al—O—C共价交联作用,构建协同增强体系,赋予T-WP-PVA/LDH复合材料优异的力学性能。木质层状复合材料优异的特性使其在包装、地膜、一次性餐盒等领域具有广泛应用前景,有望替代部分聚乙烯、聚丙烯等石油基产品。

白炭黑增强天然橡胶的热氧再生

研究了使用少量大豆油溶胀白炭黑增强天然橡胶(SNR)在不同温度和时间下的再生规律,并测定了再生产物的化学组分和微观形态。结果表明,在160~240℃温度范围内,经过20份(质量)大豆油溶胀后的SNR中溶胶含量随着温度升高而不断增加,当在220℃时再生15 min后再生产物中溶胶质量分数增至50.5%,而在200℃时再生产物中溶胶质量分数仅为28.7%,表明220℃是SNR再生中重要的转折温度;再生产物中氧元素含量的增加源于SNR在再生过程中发生了剧烈的氧化反应。此外,随着再生程度的增加,白炭黑表面松散层结合胶层厚由25 nm减至8 nm,表明热氧再生能够实现纳米白炭黑与其表面结合胶的高度剥离。

聚羟基脂肪酸酯/氧化石墨烯复合材料的制备及性能表征

采用熔融机械共混技术制备了聚羟基脂肪酸酯(PHA)/氧化石墨烯(GO)复合材料,通过拉伸性能测试、差示扫描量热分析、X射线衍射和扫描电子显微镜表征等手段,系统研究了GO对PHA基体材料力学性能、热性能、结晶行为和微观形貌的影响。结果表明,适量GO(0.04%)的引入可显著提高PHA的拉伸强度和断裂伸长率。PHA/GO复合材料的结晶度均随GO含量的增加而提高,说明GO能够促进PHA的结晶。GO在PHA基体中分散良好,与PHA基体具有良好的相容性。综上所述,GO是一种理想的PHA基体增强增韧改性剂。

无机氧化物填料对硅橡胶泡沫材料力学和阻燃性能的影响

以氧化铜、二氧化钛和高岭土作为无机增强填料,分别与羟基、乙烯基和含氢硅油进行复合,在室温和铂催化下,通过硅氢加成和硅氢缩合脱氢反应制备了一系列硅橡胶泡沫复合材料,探讨了不同无机填料对硅橡胶泡沫材料微观形貌、力学和阻燃性能的影响,以及泡孔结构与力学和阻燃性能的关系。结果表明,高岭土能够更好地分散于硅橡胶泡沫材料中,还能明显增强材料的力学和阻燃性能,热释放量和产烟量显著下降。与空白硅橡胶泡沫材料相比,含高岭土硅橡胶泡沫材料的拉伸强度、扯断伸长率、压缩强度、极限氧指数及UL-94等级分别提升至106.1 kPa、42.3%、35.2 kPa、32.7%和V-0级,总热释放量和总产烟量分别下降了51.1%和84.2%。

氧化石墨烯对水泥基复合材料微观结构和力学性能的影响（英文）

研究了不同掺量下氧化石墨烯(GO)对水泥石以及胶砂微观结构和力学性能的影响。含16.5%水的水泥浆、0.05%GO及3倍于水泥的沙子共混物作为添加剂制备成砂浆。通过SEM、液氮吸附仪和一系列标准实验分别对水泥石的微观形态、孔隙结构、抗压抗折强度以及水泥净浆的流动度、黏度、凝结时间进行表征;考察不同GO掺量下水泥水化放热的变化情况。结果表明:GO对水泥浆有显著增稠和促凝作用;GO的掺入可以有效降低水泥的水化放热量;GO对水泥石有显著的增强增韧效果,28天龄期时,GO质量分数为0.05%的水泥石,3、7和28 d抗压强度和抗折强度同比对照组分别增加52.4%、46.5%、40.4%和86.1%、68.5%、90.5%,胶砂的抗压强度和抗折强度同比对照组分别增加43.2%、33%、24.4%和69.4%、106.4%、70.5%;GO在水泥硬化过程中对水泥石中晶体产物的产生有促进作用并能规整晶体的排布而形成针状晶体簇,改善水泥石中的孔结构,降低水泥石中微孔的体积,增加水泥石的密实度,对水泥石有显著地增强增韧效果。