Properties of CNTs/MoSi2 composites prepared by spark plasma sintering

Molybdenum disilicide(MoSi_2) based composites with various contents of carbon nanotubes(CNTs) were fabricated by spark plasma sintering(SPS) in vacuum under a pressure of 25 MPa.The composites obtained under a sintering temperature of 1500 °C and time of 10 min exhibited optimum mechanical properties at room temperature in terms of fracture toughness and transverse rupture strength.MoSi_2 based composite with 6.0% CNTs(volume fraction) had the highest fracture toughness,transverse rupture strength and hardness,which were improved by about 25.7%,51.5% and 24.4% respectively,as compared with pure MoSi_2.A Mo_(4.8)Si_3C_(0.6) phase was detected in CNTs/MoSi_2 composites by both X-ray diffraction(XRD) method and microstructure analysis with scanning electron microscopy(SEM).It is believed that the fine grains and well dispersed small Mo_(4.8)Si_3C_(0.6) particles had led to a higher hardness and strength of CNTs/MoSi_2 composites because of their particle pullout,crack deflection and micro-bridging effects.

Effect of porous structure on mechanical properties of C/PLA/nano-HA composites scaffold

Nonporous and porous C/PLA/nano-HA composites were fabricated by the process of solvent blending and freeze-drying technique, and the effect of porous structure on the mechanical properties of C/PLA/nano-HA composites scaffold was investigated and analyzed. The results show that the effects of porous structure on the bending strength, modulus and curves of stress and strain were obvious. Compared with nonporous sample, the curves of stress and strain of porous sample show more rough, and alternative phenomenon of stress increase and stress relaxation appears. It is strongly suggested that the fracture model of C/PLA/nano-HA composites scaffold transforms from the local to global load due to the porous structure.

Influence of thermomechanical processing on the structure and properties of Cu-Ag alloy in situ composites

The influences of the thermomechanical processing, including the solidification conditions, the cold deformation and the intermediate annealing treatment, on the structure and properties of the Cu-10Ag alloy in situ composite were studied in this paper. The cast structure and the structural changes in the cold deformation and intermediate annealing process were observed. The properties including the ultimate tensile strength (UTS) and the electrical conductivity were determined. A two-stage strain strengthening effect for the Cu-10Ag alloy in situ filamentary composite was observed. The factors influencing the UTS and conductivity were discussed. The solidification conditions in the range of 10-1000 K/s cooling rates and the intermediate heat treatment showed obviously influence on the structure and properties on the Cu-10Ag alloy in situ filamentary composite. The typical properties of the Cu-Ag alloy in situ filamentary composites through thermomechanical processing were reported.

Microstructure and Mechanical Performance of Cu-SnO_2-rGO based Composites Prepared by Plasma Activated Sintering

A novel chemical technique combined with unique plasma activated sintering（PAS） was utilized to prepare consolidated copper matrix composites（CMCs） by adding Cu-SnO2-rGO layered micro powders as reinforced fillers into Cu matrix. The repeating Cu-SnO2-rGO structure was composed of inner dispersed reduced graphene oxide（r GO）, SnO2 as intermedia and outer Cu coating. SnO2 was introduced to the surface of rGO sheets in order to prevent the graphene aggregation with SnO2 serving as spacer and to provide enough active sites for subsequent Cu deposition. This process can guarantee rGO sheets to suffi ciently disperse and Cu nanoparticles to tightly and uniformly anchor on each layer of rGO by means of the SnO2 active sites as well as strictly control the reduction speed of Cu^2＋. The complete cover of Cu nanoparticles on rGO sheets thoroughly avoids direct contact among rGO layers. Hence, the repeating structure can simultaneously solve the wettability problem between rGO and Cu matrix as well as improve the bonding strength between rGO and Cu matrix at the well-bonded Cu-SnO2-rGO interface. The isolated rGO can effectively hinder the glide of dislocation at Cu-rGO interface and support the applied loads. Finally, the compressive strength of CMCs was enhanced when the strengthening effi ciency reached up to 41.

A machine-learning-enabled approach for bridging multiscale simulations of CNTs/PDMS composites

Benefitting from the interlaced networking structure of carbon nanotubes(CNTs),the composites of CNTs/polydimethylsiloxane(PDMS)have found extensive applications in wearable electronics.While hierarchical multiscale simulation frameworks exist to optimize the structure parameters,their wide applications were hindered by the high computational cost.In this study,a machine learning model based on the artificial neural networks(ANN)embedded graph attention network,termed as AGAT,was proposed.The datasets collected from the micro-scale and the macro-scale simulations are utilized to train the model.The ANN layer within the model framework is trained to pass the information from micro-scale to macro-scale,while the whole model is aimed to predict the electro-mechanical behavior of the CNTs/PDMS composites.By comparing the AGAT model with the original multiscale simulation results,the data-driven strategy is shown to be promising with high accuracy,demonstrating the potential of the machine-learning-enabled approach for the structure optimization of CNT-based composites.

Development of EPDM composites reinforced by CNTs@SiO_(2)for thermal protection systems of aerospace propulsion:Significant improvement in oxidation and ablation resistance properties

Carbon Nanotubes(CNTs)reinforced Polymer-Matrix Composites(PMCs)is widely used as insulation materials in thermal protection system of aerospace propulsion.However,CNTs are prone to oxidation and have high thermal conductivities,which makes it difficult to improve the ablation resistance of insulation materials that contain CNTs.SiO_(2)was encapsulated onto the surface of CNTs(CNTs@SiO_(2)),which were then added to Ethylene Propylene Diene Monomer(EPDM)rubber to prepare the insulation materials.Thermogravimetric analysis and ablation test were used to evaluate the resistance of the insulation materials to thermal oxidation and ablation.Additionally,scanning electron microscopy was performed to analyze their microstructures.Results revealed that the addition of CNTs@SiO_(2)could visibly reduce the effects of hot corrosion and ablation on insulation materials.The C-CNTs@SiO_(2)-1 formulation had the best ablative resistance.Further,compared with the unencapsulated formulation(C-CNTs-10),the C-CNTs@SiO_(2)-1 formulation reduced the line ablation rate by 51%to 0.0130 mm/s after oxygen-acetylene experiments.Lastly,the ablation mechanism was investigated based on the effects of the CNTs@SiO_(2)additive on their properties.Thus,the improvement in ablation performance may be attributed to CNTs@SiO_(2)-induced decreases in thermal conductivity,improvement in the hot corrosion resistance in the char layer,and changes in the microstructure.

Thermodynamic property of sandwich cylindrical shell structure with metallic wire mesh:Numerical modeling and experimental analysis

As a new addition to lightweight composite structures,the sandwich cylindrical shell with a metallic wire mesh core has emerged as a promising solution for thermodynamic performance analysis at elevated temperatures.The intricate interwoven cellular formations within the metallic wire mesh pose difficulties for thermo-mechanical modeling and property evaluation.First,the constitutive models employed to characterize hysteresis phenomena were presented,comprising isotropic elasticity,Bergstrom-Boyce model,Ogden hyper-elasticity,and parameter identification through mechanical examinations at varying temperatures.Second,the finite element modeling of cylindrical shell structures was determined for modal and steady-state dynamic analyses.Third,the experimental procedures were carried out,including the preparation of the sandwich cylindrical shell and the dynamic testing platform.The first-order natural frequency of the cylindrical shell structure is close to the resonance frequency of the dynamic test results,with a maximum error of 6.5%,demonstrating the accuracy of the simulation model.When compared to the solid-core cylindrical shell,the average insertion loss of the sandwich cylindrical shell structure within the frequency range of 10–1000 Hz at room temperature is up to 11.09 dB.Furthermore,at elevated temperatures,the average insertion loss of the sandwich cylindrical shell decreases but fluctuates as the temperature changes.

Constructing orthogonally structured graphene nanointerface on SiC nanowires reinforced carbon/carbon composites to boost mechanical strength and strength retention rate

Carbon/carbon composites with higher mechanical strength and better reliability at elevated tempera-tures are urgently needed to satisfy the practical applications requirements.SiC nanowires(SiCNWs)modified C/C(SC-CC)composites have attracted an abundance of attention for their excellent mechanical performance.To further boost the mechanical strengths of composites and maximize the reinforcing efficiency of SiCNWs,we introduce orthogonally structured graphene nanosheets(OGNs)into SC-CC composites,in which OGNs are grafted on the SiCNWs via chemical vapor deposition(CVD)method,forming SC-G-CC composites.Benefiting from the nano-interface effects,uniform stress distribution,strong SiCNWs/PyC interfacial bonding and elevated stress propagation efficiency in the PyC matrix are achieved,thus SC-G-CC composites accomplish brilliant mechanical properties before and after 1,600℃ heat treatment.As temperature rises to 2,100℃,SiCNWs lose efficacy,whereas OGNs with excellent thermal stability continue to play the nano-interface role in the PyC matrix.Therefore,SC-G-CC com-posites show better mechanical performance after 2,100℃ heat treatment,and the mechanical strength retention rate(MSR)of interlaminar shear strength,out-of-plane and in-plane compressive strength of SC-G-CC composites reach 61.0%,55.7%and 55.3%,respectively.This work proposes an alternative thought for maximizing the potentiality of nanomaterials and edifies the mechanical modification of composites.

Microstructures and properties of Cu/Ag(Invar) composites fabricated by powder metallurgy

The Ag(Invar)composite powder prepared by ball milling was used to fabricate the Cu/Ag(Invar)composites.Microstructures and properties of the composites were studied after sintering and thermo-mechanical treatment.The results indicatethat during ball milling,micro-forging weld and work-hardening fracture result in that the average particle size of the Ag(Invar)powder increases rapidly at first,and then decreases sharply,finally tends to be constant.Compared with the Cu/Invar ones,thesinterability of the composites is greatly improved,resulting in that the pores in them are smaller in amount and size.After thethermo-mechanical treatment,the Cu/Ag(Invar)composites are nearly fully dense with the optimum phase composition and elementdistribution.More importantly,Cu and the Invar alloy in the composites distribute continuously in a three-dimensional(3D)networkstructure.Cu/Invar interface diffusion is effectively inhibited by the Ag barrier layer,leading to a great improvement of themechanical and thermal properties of the Cu/Ag(Invar)composites.

Structure and Tribological Property of TiBN Nanocomposite Multilayer Synthesized by Ti-BN Composite Cathode Plasma Immersion Ion Implantation and Deposition

A Ti-BN complex cathode is made from Ti and h-BN powders by the powder metallurgy technology, and TiBN coating is obtained by plasma immersion ion implantation and deposition with this Ti-BN composite cathode. The TiBN coating shows a self-forming multilayered nanocomposite structure while with relative uniform elemental distributions. High resolution transmission electron microscopy images reveal that the multilayered structure is derived from different grain sizes in the nanocomposite. Due to the existence of h-BN phase, the friction coefficient of the coating is about 0.25.

CNTs对多道次低温轧制Mg-2Zn合金板材动态再结晶及力学性能的影响

采用多道次轧制技术制备了不同碳纳米管(CNTs)含量的Mg-2Zn基复合材料板材,利用EBSD、TEM等技术研究了板材的微观组织演变规律,结合拉伸实验分析了板材的强化机理。结果表明:在轧制过程中晶界处的CNTs能够阻碍位错运动,使位错在晶界处堆积,导致局部应力集中,促进变形孪晶的产生。变形孪晶诱发动态再结晶(DRX)发生,在孪晶内和孪晶界区域发剧烈的动态再结晶(DRX),导致终态高CNTs含量(CNTs含量为0.6%)的板材的基面织构强度趋弱。CNTs主要影响了板材的织构状态,随着CNTs含量的增加,板材的(0001)基面强度逐渐降低,从轧向(RD)向横向(TD)劈裂,降低了基面织构的强度。在CNTs、细晶和织构强化下,0.4%CNTs/Mg-2Zn复合材料的抗拉强度为283 MPa、屈服强度为260 MPa、伸长率为4%。

球磨方式对CNTs/Al复合材料显微组织与力学性能的影响

采用湿法球磨和干法球磨两种方式制备碳纳米管(carbon nanotubes,CNTs)和铝的复合粉体,再使用放电等离子烧结结合热挤压的工艺制备碳纳米管增强铝基(CNTs/Al)复合材料,系统研究了制备工艺-组织结构-材料性能之间的关系。结果表明,相较于干法球磨,湿法球磨可以更好地分散碳纳米管,且显著减少对其结构的破坏;乙醇球磨介质具有冷却作用,在减少粉体冷焊的同时有助于细化Al基体晶粒,从而使复合材料获得出色的力学性能。乙醇湿法球磨6 h后烧结并热挤压的2%CNTs/Al复合材料抗拉强度达到207 MPa。

烧结温度对CNTs/Cu复合材料组织和力学性能的影响

采用电泳沉积法在铜箔上沉积碳纳米管,层层堆叠后在不同烧结温度(550,650,750,850,950℃)下热压烧结制备碳纳米管增强铜基(CNTs/Cu)复合材料,研究了烧结温度对复合材料显微组织和力学性能的影响。结果表明:随着烧结温度升高,复合材料中孔隙的数量减少,尺寸减小,碳纳米管分布均匀性增大,铜晶粒尺寸增大,退火孪晶晶粒尺寸增大但数量减少;随着烧结温度升高,复合材料的抗拉强度和显微硬度均呈先减小后增大的趋势,断后伸长率变化呈非单调性变化;当烧结温度为650℃时,复合材料的抗拉强度和显微硬度适中,断后伸长率最大,综合力学性能最好。

STRUCTURES AND PROPERTIES IN IN-SITU COMPOSITES ITES OF LC70/PET

Structures and properties of the blends of thermotropic liquid crystallinepolymer(LC70)and poly(ethylene terephthalate) (PET) were investigated by usingWAXD,DSC,SEM and mechanical test.The results revealed that Wc,x markdly decreased withLC70/PET>30%,and at about LC70/PET=10%, this blend can yield better mechanicalproperties.In these blends LC70 can play the role of the nuclear agent for PET.SEMphoto showed that LC70/PET in in-situ composites possessed 'core-shell' structure andwas immiscible, but at LC70/PST=10%, the LC70 can be uniformly dispersed into matrix PET.

Effect of electrical current on tribological property of Cu matrix composite reinforced by carbon nanotubes

Cu matrix composite reinforced with 10%（volume fraction） carbon nanotubes（CNTs/Cu） and pure Cu bulk were prepared by powder metallurgy techniques under the same consolidation processing condition.The effect of electrical current on tribological property of the materials was investigated by using a pin-on-disk friction and wear tester.The results show that the friction coefficient and wear rate of CNTs/Cu composite as well as those of pure Cu bulk increase with increasing the electrical current without exception,and the effect of electrical current is more obvious on tribological property of pure Cu bulk than on that of CNTs/Cu composite;the dominant wear mechanisms are arc erosion wear and plastic flow deformation,respectively;CNTs can improve tribological property of Cu matrix composites with electrical current.

CNTs杂化粒子改性PP/PGA复合材料的结构与性能

为解决聚丙烯/聚乙醇酸(PP/PGA)共混物由于相容性较差导致力学性能存在局限性的问题,采用过硫酸铵-胺氧化还原引发体系,通过表面引发接枝聚合法(SIP)制备了碳纳米管接枝聚甲基丙烯酸缩水甘油酯杂化粒子(CNTs@PGMA),以CNTs@PGMA杂化粒子和聚丙烯接枝马来酸酐(PP-g-MAH)为协同增容体系,通过熔融共混法制备了PP/PGA/CNTs复合材料,采用傅里叶变换红外光谱仪和透射电子显微镜对CNTs@PGMA进行了表征,结果表明PGMA通过SIP成功接枝在CNTs表面。采用拉伸测试、差示扫描量热仪、热重分析、旋转流变和降解试验等方法研究了CNTs@PGMA用量对复合材料力学性能、热性能、降解性能和流变行为的影响。结果表明,在PP/PGA/PP-g-MAH体系中加入CNTs@PGMA后其相容性得到提升,随杂化粒子用量增加,复合材料拉伸强度先增大后减小,热稳定性得到提升,PGA结晶逐渐受限甚至无熔融峰出现。杂化粒子的加入形成了三维网络结构,提高了复合材料熔体弹性,熔体表现出更强的非牛顿性和剪切变稀行为,同时PGA的降解过程受到抑制。当CNTs@PGMA用量为5份时,复合材料的拉伸强度最大为41.25 MPa,断裂伸长率为66.03%,PGA在42 d时的降解率下降至10%以内,拉伸强度维持率达到91%。

CNTs/纳微米PZT/水泥压电复合材料的研究

研究制备了一种新型0-3CNTs/纳微米PZT/水泥压电复合材料。该复合材料的基体相为硅酸盐水泥,压电活性相为锆钛酸铅(PZT)压电陶瓷,压电增强相为纳米碳管(CNTs)。PZT采用溶胶-凝胶法合成,其粒径大多分布在几十至几百纳米之间。CNTs采用Fenton/UV法分散处理。研究了CNTs对该水泥基压电复合材料压电和介电性能的影响。CNTs可改善水泥基复合材料的导电性,使其可在室温中进行极化,提高了压电相的极化效率,从而显著提高复合材料的压电性能。0.9vol%CNTs/70vol%PZT/水泥复合材料的压电应变常数(d33)值可达到54.5pC/N,显示出该类水泥基压电复合材料用作土木领域传感器的良好前景。

CNTs/SiC/Cu复合材料制备及性能

以碳纳米管(CNTs)、碳化硅(SiC)粉体、锌(Zn)粉和CuSO4.5H2O为主要原料,用化学镀的方法制备CNTs/Cu复合粉体,再采用非均相沉淀法制备CNTs/SiC/Cu复合粉体。在750℃、100MPa的制度下进行真空热压烧结后制得CNTs/SiC/Cu复合材料,其中Cu的含量(体积分数,下同)为70%,CNTs的含量(体积分数,下同)分别为0,3%,5%,8%,12%。利用XRD、SEM分析样品的物相组成和显微结构;利用阿基米德排水法、显微硬度计、三点弯曲法测试了复合材料的密度、显微硬度和抗弯强度。结果表明,随着碳纳米管含量的增加,CNTs/SiC/Cu复合材料的密度、显微硬度和抗弯强度等性能发生相应变化,其中,抗弯强度呈现逐渐升高趋势。与未添加碳纳米管的30SiC/70Cu复合材料相比,添加12%CNTs的12CNTs/18SiC/70Cu样品,抗弯强度提高了21.45MPa。

Elastic and Plastic Behaviors of Laminated Ti-TiBw/Ti Composites

The novel laminated Ti-TiBw/Ti composites composed of pure Ti layers and TiBw/Ti composite layers have been successfully fabricated by reactive hot pressing. Herein, two-scale structures formed： the pure Ti layer and TiBw/Ti composite layer together constructed a laminated structure at a macro scale. Furthermore, TiBw reinforcement was distributed around Ti particles and then formed a network microstructure in TiBw/Ti composite layer at a micro scale. The laminated Ti-TiBw/Ti composites reveal a superior combination of high strength and high elongation due to two-scale structures compared with the pure Ti, and a further enhancement in ductility compared with the network structured composites. Moreover, the elastic modulus of the laminated composites can be predicted by H-S upper bound, which is consistent with the experimental values.

Single-source-precursor derived Sioc ceramics with in-situ formed CNTs and core-shell structured CoSi@C nanoparticles towards excellent electromagnetic wave absorption properties

In this work,novel carbon nanotube(CNT)/CoSi/SiOC nanocomposite ceramics with in-situ formed multi-walled CNTs and core-shell structured CoSi@C nanoparticles were successfully prepared via a single-source-precursor derived ceramic approach.Ppolymericprecursor characterization as well as phase evolution,microstructure,and electromagnetic wave(EMW)absorption properties of the ceramics were investigated in detail.The results show that the in-situ formed CNTs and magnetic CoSi@C nanoparticles provide a synergistic effect on both dielectric loss(tand:)and magnetic loss,leading to outstanding EMW absorption properties of the ceramics annealed at only 1100 C.(i)For the Co feeding of 6.25 wt%,the minimum reflection loss(RLmin)is-53.1 dB,and the effective absorption bandwidth(EAB)is 4.96 GHz(7.12-12.08 GHz)with a ceramic-paraffin hybrid sample thickness of 3.10 mm,achieving full X-band coverage;(i)for the Co feeding of 9.09 wt%,the RLmin value of-66.4 dB and the EAB value of 3.04 GHz(8.40-11.44 GHz)were achieved with a thickness of only 2.27 mm.Therefore,the present CNT/CoSi/SiOC nanocomposite ceramics have potential applications for thin,lightweight,and efficient EMW absorption in harsh environments.