Flexural behavior of composite beams after the ultimate limit state externally strengthened with CFRP sheets bonded with high-temperature resistant matrix

In this paper the alkali-activated slag cementitious materials(AASCM)which strength at 600 ℃ is larger than that of AASCM at room temperature,were prepared to paste CFRP sheets to strengthen four simply supported unbonded prestressed composite beams encased circular steel tube truss after ultimate limit state.Test on flexural behavior of these four beams was performed.Moreover,normal section load-bearing capacity of these beams and the curve load-deflection at mid-span were obtained.Experimental results show that it is feasible to strengthen concrete members with CFRP sheets bonded with AASCM.Based on the experimental results and theoretical study,computational method of stiffness is proposed for calculating bending rigidity and normal section load-bearing capacity of concrete simply supported beams strengthened with CFRP sheets bonded with AASCM.Formula of bending rigidity calculation was founded which results are in good agreement with testing data.

Pt-Al₂OM₃Composite Material Designed for Cyclic Production of Optical Glasses under High Temperature Conditions

The article considers one of the possible approaches to the solution of an urgent issue of metal consumption reduction, increase of operating life and maximum operating temperature as well as reduction of irrecoverable losses of platinum products and alloys when operating under high temperature conditions, particularly for glassblowing and single crystal growing crucibles. A two-layered composite material based on platinum-group metals and corundum plasma ceramics is thoroughly investigated. A successful experience of crucibles exploitation, designed for production of high temperature optical glasses from the composite and results of the research on composite material specimens are described.

Experimental investigation of high temperature thermal contact resistance with interface material

Thermal contact resistance plays a very important role in heat transfer efficiency and thermomechanical coupling response between two materials,and a common method to reduce the thermal contact resistance is to fill a soft interface material between these two materials.A testing system of high temperature thermal contact resistance based on INSTRON 8874 is established in the present paper,which can achieve 600 C at the interface.Based on this system,the thermal contact resistance between superalloy GH600 material and three-dimensional braid C/C composite material is experimentally investigated,under different interface pressures,interface roughnesses and temperatures,respectively.At the same time,the mechanism of reducing the thermal contact resistance with carbon fiber sheet as interface material is experimentally investigated.Results show that the present testing system is feasible in the experimental research of high temperature thermal contact resistance.

结构钢电沉积Co-W/CeO_(2)复合镀层及其性能研究

选择CeO_(2)颗粒作为复合相,利用电沉积技术在普通结构钢表面制备出Co-W/CeO_(2)复合镀层,并研究镀液中CeO_(2)颗粒浓度对复合镀层的微观形貌、化学成分、结合力、硬度、耐磨性能以及高温抗氧化性能的影响。结果表明:Co-W/CeO_(2)复合镀层与基体结合牢固,表面分布着类似胞状的晶粒团聚体,其化学成分为Co、W、Ce和O元素。随着镀液中CeO_(2)颗粒浓度从2 g/L升高到15 g/L,复合镀层的晶粒团聚体尺寸差异先减小后增大,吸附在晶粒团聚体表面及边界处的CeO_(2)颗粒量先增多后减少,导致复合镀层的硬度、耐磨性能和高温抗氧化性能都呈先增强后下降的趋势。当镀液中CeO_(2)颗粒浓度为8g/L时,Co-W/CeO_(2)复合镀层的晶粒团聚体大小较为均匀,具有良好的致密性,其表面粗糙度仅为0.39μm。该复合镀层的硬度较Co-W合金镀层增大约76 HV,表现出良好的耐磨性能和高温抗氧化性能,摩擦系数和氧化增重量仅为0.43和0.74mg/cm^(2)。

Oxidation behavior of in-situ Al_2O_3/TiAl composites at 900°C in static air

In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2＋Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.

SiO_(2)-BNNSs杂化材料对磷酸盐复合涂层高温摩擦学性能的影响

目的通过在磷酸盐复合涂层中添加二氧化硅杂化氮化硼纳米片材料(SiO_(2)-BNNSs)来提升磷酸盐复合涂层的硬度和耐高温磨损性能。方法以正硅酸四乙酯(TEOS)为硅源,利用溶胶凝胶法制备SiO_(2)-BNNSs杂化材料,并作为纳米增强相加入到涂层中。通过X射线光电子能谱(XPS)、场发射扫描电子显微镜(FE-SEM)和透射电子显微镜(TEM)对SiO_(2)-BNNSs杂化材料的化学组成和微观形貌进行表征。另外,采用喷涂法制备不同含量BNNSs和SiO_(2)-BNNSs的磷酸盐复合涂层,通过高温摩擦磨损试验探究涂层的摩擦磨损行为,对涂层磨痕形貌进行表征,并探讨涂层在高温条件下的磨损机理。结果XPS、SEM和TEM的分析结果表明,SiO_(2)成功修饰在BNNSs表面。SiO_(2)-BNNSs磷酸盐涂层相比零含量BNNSs涂层和纯BNNSs涂层表现得更加均匀致密,400℃条件下,质量分数为0.4%的SiO_(2)-BNNSs涂层硬度高达261.2HV。高温摩擦试验表明,BNNSs和SiO_(2)-BNNSs的加入,可以减轻涂层的磨损现象。同时,温度越高,涂层的耐磨损性能越好,400℃条件下,0.4%SiO_(2)-BNNSs涂层的摩擦因数和磨损率分别为0.48和66.24×10–6mm^(3)/(N·m),耐高温磨损性能表现为最佳。结论SiO_(2)-BNNSs杂化材料的添加可以明显提升磷酸盐复合涂层的耐高温磨损性能。

High-temperature oxidation behavior of Al_2O_3/TiAl matrix composite in air

The oxidation behavior of Al2O3/TiAl in situ composites fabricated by hot-pressing technology was in-vestigated at 900℃ in static air.The results indicate that the mass gains of the composites samples decrease gradually with increasing Nb2O5 content and the inert Al2O3 dispersoids effectively increase the oxidation resistance of the composites.The higher the Al2O3 dispersoids content,the more pro-nounced the effect.The primary oxidation precesses obey approximately the linear laws,and the cyclic oxidation precesses follow the parabolic laws.The oxidized sample containing Ti2AlN and TiAl phases in the scales exhibits excellent oxidation resistance.The oxide scale formed after exposure at 900 ℃ for 120 h is multiple-layered,consisting mainly of an outer TiO2 layer,an intermediate Al2O3 layer,and an inner TiO2+Al2O3 mixed layer.From the outer layer to the inner layer,TiO2+Al2O3 mixed layer presents the transit of Al-rich oxide to Ti-rich oxide mixed layer.Near the substrate,cross-section micrograph shows a relatively loose layer,and micro-and macro-pores remain on this layer,which is a transition layer and transferres from Al2O3+TiO2 scale to substrate.The thickness of oxide layer is about 20 μm.It is also found that continuous protective alumina scales can not be observed on the surface of oxida-tion scales.Ti ions diffuse outwardly to form the outer TiO2 layer,while oxygen ions transport inwardly to form the inner TiO2+Al2O3 mixed layer.Under long-time intensive oxidation exposure,the internal Al2O3 scale has a good adhesiveness with the outer TiO2 scale.No obvious spallation of the oxide scales occurs.The increased oxidation resistance by the presence of in situ Al2O3 particulates is at-tributed to the enhanced alumina-forming tendency and thin and dense scale formation.Al2O3 particu-lates enhance the potential barrier of Ti ions from M/MO interface to O/MO interface,thereby the TiO2 growth rate decreases,which is also beneficial to improve the oxidation resistance.Moreover,the multi-structure of the TiO2+Al2O3 mixed layer decreases the indiffusion of oxygen ions and also avails to improve the high temperature oxidation resistance of the as-sintered composites.

C/C多孔体的高温热处理对C/C-SiC复合材料摩擦磨损行为的影响

低密度C/C多孔体的结构与性能调控是制备具有优异摩擦磨损性能的C/C-SiC复合材料的关键。本研究采用化学气相渗积法制备了C/C多孔体,并对其进行2100℃高温热处理,再通过反应熔渗法制备了C/C-SiC复合材料,研究了C/C多孔体高温热处理对C/C-SiC复合材料微观结构、导热性能和摩擦磨损性能的影响。结果表明,经2100℃热处理的C/C多孔体孔隙率和石墨化程度增加,用其制备的C/C-SiC复合材料比C/C多孔体未经热处理的密度更大(2.22 g/cm^(3)),孔隙率由5.1%降低至3.4%, SiC陶瓷相含量比热处理前提高11.9%。石墨化程度越高,声子的平均自由程越大,因此其室温的导热率提升到3.1倍, 1200℃导热率提升到1.2倍。经过热处理的热解炭更软,摩擦面易形成连续且稳定的摩擦膜,因此摩擦系数更稳定,并且在测试载荷为3、6和9 N下磨损率均显著降低,下降幅度达到47.8%、41.9%和11.7%,平均摩擦系数分别为0.47、0.38和0.39。综上所述,对C/C多孔体进行高温热处理可使C/C-SiC复合材料的导热性能提升,更耐磨并且表现出更稳定的摩擦系数。

Wear Performance of Ni/ZrO_2 Infiltrated Composite Layer

The Ni/ZrO2 was used as raw materials to fabricate the surface infiltrated composite layer with 1-4 mm thickness on cast steel substrate through vacuum infiltrated casting technology. The microstructure indicated that the infiltrated composite layer included surface composite layer and transition layer. Wear property was investigated under room temperature and 450 ~C. The results indicated that the abrasion volume of substrate was 8 times that of the infiltrated composite layer at room temperature. The friction coefficient of infiltrated composite layer decreased with the increasing load. The wear resistance of infiltrated composite layer with different ZrO2 contents had been improved obviously under high temperature. The friction coefficient of infiltrated composite layer was decreased comparing with that at room temperature. The oxidation, abrasive and fatigue abrasion was the main wear mechanism at room temperature. Oxidation abrasion, fatigue wear and adhesive wear dominated the wearin~ process under elevated temperature.

非晶态α-烯烃共聚物/丁苯橡胶复合改性沥青的高温流变特性

采用热塑性树脂类改性剂非晶态α-烯烃共聚物(APAO)和丁苯橡胶(SBR)对沥青进行改性制备了APAO/SBR复合改性沥青,测试了其基本性能,同时采用布氏黏度仪和动态剪切流变仪考察了APAO与SBR的质量比对复合改性沥青高温流变特性的影响。结果表明,随着APAO用量的增加,APAO/SBR复合改性沥青的针入度、延度、质量损失率和相位角逐渐减小,软化点、黏度和车辙因子逐渐增大;APAO可以提升沥青的高温抗车辙性能,APAO/SBR复合改性沥青呈现出剪切变稀的现象。

石墨烯-羧基化碳纳米管水泥基复合材料的高温力学性能研究

测试了不同质量比的石墨烯-羧基化碳纳米管(G-CNT)水泥基复合材料在25、200、400、600℃下的质量损失、抗压强度和抗折强度。结果表明:400℃以内,添加G-CNT复合材料后水泥基复合材料的残余力学性能显著提高,对质量损失的影响较小,水泥基复合材料的耐高温性能提高;400℃时,掺入0.10%CNT和0.05%G的水泥基复合材料的抗压强度仅下降了21.43%;400~600℃时,结合XRD和SEM结果可知,水泥基复合材料的微观结构严重破坏,力学性能显著下降;G5C10组为最佳配比,25~400℃时,在最佳配比下,G、CNT复掺后可以延缓或抑制因为高温爆裂引起的微孔隙和裂缝的扩散,形成致密化结构,进而提高水泥基复合材料的耐高温性能。

活化煤废料替代水泥制备混凝土的基本特性

这是一篇陶瓷及复合材料领域的论文。为探索煤废料替代水泥进行混凝土制备的可行性,利用活性化处理的煤渣粉和煤矸石粉按照0、10%、20%、30%和40%的比例替代水泥进行混凝土试样的制备并对混凝土试样的坍落度、抗压和抗折强度进行测试,同时耐高温性能实验,结果证明:随着替代比的增加,坍落度、抗压强度和抗折强度均先增后减;煤废料的较优替代比为20%~30%。活化煤渣粉试样的早期强度增长率大;而活化煤矸石粉试样的长期强度增长率较大。当水灰比=0.45时,试样的抗压强度随着温度的升高先增后减,在100℃时达到极大值;当水灰比=0.5时,混凝土试样的抗压强度均随着温度的升高逐渐降低;活性煤渣粉试样界面区域的水合胶结构较最多,对照组次之,活化煤矸石粉试样较少。随着温度升高,试样表面的孔隙和裂缝明显增多且破坏面的破碎程度逐渐加剧。

超高温陶瓷复合材料研究进展

随着高速飞行器朝着更宽空域、更长时间和更高速度的方向发展,对飞行器的鼻锥、前缘和发动机燃烧室等关键结构的热防护性能提出了更加严苛的要求,发展在极端环境下使用的高性能热防护材料是当前的研究重点。超高温陶瓷复合材料具有优异的抗氧化烧蚀性能,是一类极具应用潜力的非烧蚀型热防护材料。然而,本征脆性问题限制了超高温陶瓷复合材料的工程化应用,需通过组分结构调控对其进行强韧化。同时,飞行器有效载荷提升也对超高温陶瓷复合材料提出了轻量化的要求。本文系统概述了超高温陶瓷复合材料近年来取得的主要研究进展,包括压力烧结、泥浆浸渍、前驱体浸渍裂解、反应熔渗、化学气相渗透/沉积与“固-液”组合工艺等制备方法,颗粒、晶须、软相物质、短切纤维和连续纤维等强韧化方法及其机制,抗氧化烧蚀性能与机理,以及轻量化设计等。讨论了超高温陶瓷复合材料组分、微结构和性能之间的关系,并指出了超高温陶瓷复合材料目前存在的挑战以及未来的发展趋势。

AlO(OH)/聚酰亚胺复合薄膜的制备及其耐高温性能研究

以4,4′-二氨基二苯醚为二胺单体,均苯四甲酸二酐为酸酐单体,3-氨基丙基三乙氧基硅烷(KH550)为偶联剂,异丙醇铝[Al(OPri)3]为铝源,采用溶胶-凝胶法制备以聚酰亚胺(PI)为基体,AlO(OH)为增强相的PI复合薄膜。利用扫描电子显微镜(SEM)、傅里叶变换红外光谱、X射线衍射、热重分析仪、差示扫描量热仪、水接触角仪、漆膜划格器、铅笔划痕实验仪等对复合薄膜的结构和性能进行表征。结果表明,随着铝溶胶含量的增加,复合薄膜的热稳定性呈现先上升后降低的趋势。当铝溶胶含量为10%时,AlO(OH)/PI复合薄膜具有最好的耐高温性能,其热分解5%时的温度达到567℃,玻璃化转变温度为381.4℃。

高掺量胶粉/SBS改性沥青及其混合料的路用性能

为了提高废旧轮胎利用率,降低沥青生产成本,发挥胶粉和SBS两种改性沥青的优势,通过优化制备工艺和材料掺量,研究沥青的三大指标、黏度、弹性恢复、储存稳定性,确定了胶粉/SBS复合改性沥青的胶粉最佳掺量为42%,裂解剂的最佳掺量为1.5%。以制备的高掺量复合改性沥青混合料为主要研究对象,其他5种沥青混合料为对照组,包括基质沥青混合料、3%SBS改性沥青混合料、21%普通掺量的胶粉改性沥青混合料、42%高掺量胶粉改性沥青混合料以及21%胶粉+3%SBS普通掺量复合改性沥青混合料,通过车辙试验、低温小梁弯曲试验等分析各个改性沥青混合料的性能。结果表明,比起其他5种沥青混合料,高掺量胶粉/SBS复合改性沥青混合料有优异的高温抗车辙、低温抗开裂和水稳定性,为进一步研究胶粉/SBS改性沥青的应用起到了推广作用。

激光熔覆NiCr/Cr_3C_2-WS_2自润滑耐磨涂层的高温摩擦学行为

利用激光熔覆技术在0Cr18Ni9不锈钢基体上制备NiCr/Cr3C2耐磨涂层与NiCr/Cr3C2-30%WS2耐磨自润滑涂层,采用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、能谱仪(EDS)分析了涂层的物相组成及显微组织。在室温、300℃和600℃下分别测试了上述涂层的干滑动摩擦学性能,并讨论其磨损机理。实验结果表明:添加WS2的熔覆涂层主要有Cr7C3、(Cr,W)C碳化物增强相、γ-(Fe,Ni)/Cr7C3共晶增韧相、WS2及CrS润滑相。两种涂层都随温度的升高,摩擦因数降低,而磨损率增大。在室温及300℃时,添加WS2涂层由于润滑相的作用拥有较好的减摩耐磨性能。在600℃时,由于涂层中碳化物硬质相的强度降低,两种涂层的磨损率显著增大。

电沉积RE-Ni-W-B-B_4C-MoS_2复合镀层的性能研究

研究了RE Ni W B B4 C MoS2 复合镀层在不同氧化温度和时间下的抗高温氧化性。结果显示 ,当温度小于80 0℃时 ,RE Ni W B B4 C MoS2 复合镀层被氧化的程度较小 ;温度超过 80 0℃ ,氧化膜的增重呈直线增加。RE Ni W B B4 C MoS2 复合镀层的硬度随着热处理温度的升高而增加 ,当热处理温度达到 4 0 0℃时 ,复合镀层的硬度升到极大值 (136 8HV) ;若继续升高温度 ,镀层硬度逐渐降低。RE Ni W B B4 C MoS2 复合镀层的耐磨性经 4 0 0℃热处理后最好。工艺条件对RE Ni W B B4 C MoS2 复合镀层的表面形貌影响较大 ,随着电流密度或镀液温度的升高 ,复合镀层结晶粗 ,晶粒大 ;反之 ,镀层结晶细 ,表面晶粒细小。RE Ni W B B4 C MoS2 复合镀层的镀态下以非晶态为主 ,部分已晶化 ;当经 5 0 0℃热处理后 ,复合镀层已晶化 ;经 80 0℃热处理后 ,CeO2 和B4 C仍以化合物的形式存在 ,由此可以说明 ,CeO2 和B4 C的加入 ,可以提高RE Ni W B B4 C MoS2

Ti-6Al-4V钛合金表面激光熔覆自润滑耐磨涂层的高温稳定性

以NiCr/Cr3C2-10%CaF2(质量分数,%)复合粉末为原料,采用激光熔覆技术在Ti-6Al-4V合金表面成功制备出了γ-NiCrAlTi/TiC/CaF2高温自润滑耐磨复合涂层。为研究该复合涂层的高温稳定性,在600℃下分别对该复合涂层保温24、48、96 h,并分别研究了不同保温时间下复合涂层的物相、显微硬度、摩擦学性能的变化及其机理。结果表明:高温处理前后复合涂层物相组成基本不变,由于γ-NiCrAlTi固溶体的溶解,涂层显微硬度下降约110 HV0.3;高温处理前后涂层的摩擦系数及磨损率变化较小,在长时间高温保温情况下,涂层的组织和摩擦学性能都表现出良好的高温稳定性。

浆料浸渍法制备C/C-SiC-ZrB_2超高温复合材料及其烧蚀性能研究

采用浆料浸渍法引入ZrB2微粉作为耐超高温相,以炭纤维为增强体,以热解炭和SiC为基体,制备了ZrB2含量不同的耐超高温C/C-SiC-ZrB2复合材料;通过电弧风洞考核材料的抗烧蚀性能,通过XRD、SEM和EDS分析材料的烧蚀机理。结果表明:在Ma 6电弧风洞条件下,C/C-SiC-ZrB2复合材料的抗烧蚀性能优于C/C-SiC,且随着ZrB2含量的增加,抗烧蚀性能随之提高;在高温阶段形成的ZrO2-SiO2玻璃态熔融层起到了抗氧化烧蚀的作用。

双(N-间乙炔基苯基邻苯二甲酰亚胺)醚改性甲基二苯乙炔基硅烷

甲基二苯乙炔基硅烷(MDPES)聚合后具有耐高温、低介电损耗等优异性能,但力学性能低。采用双(N-间乙炔基苯基邻苯二甲酰亚胺)醚(DAIE)添加到MDPES中进行共聚改性。通过二者不同质量配比的共聚反应发现,当MDAIE/MMDPES=4∶5时,共聚后改性效果较好,在氮气中的Td5(质量损失5%时的温度)为467℃,800℃时质量保留率为82.7%,所制备的复合材料在常温下弯曲强度达到274 MPa;高温弯曲强度保留率为88.5%。在频率为1 MHz时介电常数为4.18,介电损耗角正切tanδ为2.5×10-3。