Fabrication and characterization of GNPs and CNTs reinforced Al7075 matrix composites through the stir casting process

This study investigated the effects of adding graphene nanoplates(GNPs)and carbon nanotubes(CNTs)into the Al7075 matrix via the stir casting method on the microstructure and mechanical properties of the fabricated composites.By increasing the volume fraction of rein-forcements,the fraction of porosity increased.The X-ray diffraction results showed that the addition of reinforcements into the Al7075 changed the dominant crystal orientation from(002)to(111).Field emission scanning electron microscopy images also showed the distribution of clustered reinforcements in the matrix.Between the two reinforcements,the addition of CNTs generated a lower fraction of porosities.Through the addition of 0.52vol%GNPs into the matrix,the hardness,ultimate tensile strength and uniform elongation increased by 44%,32%,and 180%,respectively.Meanwhile,the presence of 0.71vol%CNTs in the matrix increased the hardness,tensile strength and uniform elongation by 108%,129%,and 260%,respectively.

GNPs含量对Al-Si-Cu合金的摩擦磨损性能的影响

在本研究中,利用金相显微镜(OM),扫描电子显微镜(SEM),能谱分析仪(EDS),显微硬度计和摩擦磨损试验机对GNPs(石墨烯片)/Al-Si-Cu复合材料的显微组织、显微硬度和摩擦磨损性能等进行了分析和表征。研究结果表明:随着GNPs的含量的逐渐增加,磨损率和摩擦系数均呈现出先减小再增大的趋势。当GNPs的含量为12 vol.%时,复合材料中的Si相明显得到了细化,由基体合金的长条状变为复合材料的短棒状。此时复合材料的磨损率和摩擦系数均最小,分别为21.27×10^(-3) mm^(3)/m和0.358,与Al-Si-Cu基体合金相比分别降低了37.07%和15.76%,复合材料的耐磨性能达到最佳。Al-Si-Cu基体合金是以剥层磨损为主要磨损机理,其磨屑是以大尺寸的板块状磨屑为主,而12 vol.%GNPs/Al-Si-Cu复合材料是以磨粒磨损为主要磨损机理,其磨屑则是以小尺寸板块状和细颗粒为主。

Microstructure,mechanical properties and corrosion performance of selective laser melting Ti/GNPs composite with a porous structure

In this study,nano-graphene reinforced titanium matrix composites(GNPs/Ti)with a honeycomb porous structure were fabricated by selective laser melting(SLM).The effects of graphene on the microstructure,mechanical properties and corrosion performance of the SLM GNPs/Ti were systematically investigated.Results of microstructure characterization show that:1)the density of the SLM GNPs/Ti was improved as compared to that of the SLM Ti;2)abundant TiC particles were formed in the SLM GNPs/Ti.The hardness and compressive strength of the composite increased by 90%(from HV 236 to HV 503)and 14%(from 277 MPa to 316 MPa),respectively,attributed to the uniformly distributed TiC and fine GNPs in the Ti matrix.Electrochemical tests reveal that the corrosion current density of the SLM GNPs/Ti is only 0.328μA/cm^(2),that is about 25%less than that of the SLM Ti.The results indicate that the incorporation of nano-graphene is a potential method to strengthen the Ti by SLM.

Ameliorating the Strength-Modulus Synergy in GNPs Reinforced Mg-Zn-Zr Composites via Multidirectional Forging and Hot Extrusion Deformation

The integration of lightweight and high-modulus magnesium-based materials is becoming increasingly valued as structural materials due to the complexity and intelligence of industrial products like automobiles and electronics.In this study,the graphene nanoplatelets(GNPs)/Mg-Zn-Zr composites with 0.5 wt%GNPs were successfully prepared by the combination of multidirectional forging(MDF)and hot extrusion(Ex).The newly-developed composites after multi-step deformation possessed excellent strength and modulus,with a tensile strength exceeding 375 MPa and an elastic modulus reaching 54 GPa.The results revealed that the stripping and thinning of GNPs bands parallel to the extrusion direction occurred after MDF+Ex,which promoted the dynamic recrystallization and the formation of numerous fine grains.The significant improvement in comprehensive mechanical performances of the composites could be primarily ascribed to the refinement of grain size caused by the optimized distribution of GNPs,and efficient load transfer facilitated by the tight interface.

GNPs-Cu/Ti6Al4V复合材料热压烧结工艺优化及组织性能

以TC4钛合金粉为基体,石墨烯(GNPs)为增强相,采用真空热压法制备了质量分数为0.3%的GNPs-Cu/Ti6Al4V复合材料。通过正交试验探讨了烧结温度、压力、保温时间对复合材料相对密度、显微硬度和抗压强度的影响。结果表明:烧结温度是影响复合材料相对密度、显微硬度和抗压强度的关键因素,压力和保温时间对其影响较小。最优的烧结工艺为温度1150℃、压力35 MPa和保温时间40 min,此时复合材料的相对密度、显微硬度和抗压强度最佳,分别为99.34%,585.4 HV0.1和2382 MPa。GNPs-Cu/Ti6Al4V复合材料中主要除α-Ti和β-Ti外,还存在TiC和Ti_(2)Cu相,在其压缩断口有较完整GNPs存在。

Hot Deformation Behavior and Microstructures Evolution of GNP-Reinforced Fine-Grained Mg Composites

Graphene nanoplates(GNPs)-reinforced magnesium matrix composites have been attracted great attention.However,knowledge is lack for the hot deformation behavior of GNP-reinforced magnesium(GNPs/Mg)composite.In this study,the fine-grained GNPs/Mg composite was fabricated by powder metallurgy process followed by extrusion.The hot deformation behavior,microstructure evolution and dynamic recrystallization(DRX)mechanism of fine-grained GNPs/Mg composite were investigated by hot compression test and electron back-scatter diffraction(EBSD).The hot compression tests of the composite were conducted at temperatures between 423 and 573 K with the strain rates from 0.001 to 1 s^(-1).The strain compensated power law equation was established to describe the hot deformation behavior of the composites.The stress exponent and activation energy of the composite are 7.76 and 83.23 kJ/mol,respectively,suggesting that the deformation mechanism is grain boundary slip controlled dislocation climb creep.The abnormally high stress exponent and activation energy are unattainable in the composite due to the fine grain size of the composites and the absence of Zener pinning and Orowan effects of GNPs reinforcement.The grain size increases with the decrease in Zener-Hollomn(Z)parameter,which can be well fitted by power-law relationship.With the increase in grain size and decrease in Z parameter,the geometrically necessary dislocation density decreases,which shows the approximately power-law relationship.A random and weak texture was formed after hot compression.The discontinuous dynamic recrystallization and continuous dynamic recrystallization mechanism dominated the DRX behavior at 473 K/0.001 s^(-1) and 573 K/0.001 s^(-1),respectively.

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates prepared by ultrasonic assisted casting

Microstructure and mechanical properties of ADC12 composites reinforced with graphene nanoplates(GNPs)prepared by high-intensity ultrasonic assisted casting were investigated.The results indicated that high-intensity ultrasound can promote the uniform distribution of GNPs in the melt,resulting in refining theα(Al)phase and Si phase.The optimal addition of GNPs was 0.9 wt.%,and the optimal ultrasonic time was 12 min.The tensile strength,the yield strength and the hardness of the composite produced under the optimal parameters were 256.8 MPa,210.6 MPa and HV 126.0,respectively,which increased by 30.5%,42.7%,and 34.8%compared with those of the matrix,respectively.After adding the GNPs,the fracture mechanism gradually turned from a brittle fracture to a ductile fracture.The good interface and distribution allowed GNPs to play the role in fine grain strengthening,dislocation strengthening and load transfer strengthening effectively.

(GNPs+B)/TC4复合材料组织和硬度研究

采用放电等离子烧结技术(SPS),制备石墨烯纳米片(GNPs)、硼粉(B)增强TC4钛基复合材料(TiMCs)。利用扫描电镜、拉曼光谱对混合粉末以及烧结后材料的组织进行了研究。利用维氏硬度仪对复合材料进行硬度测试。结果表明:GNPs和B与基体原位反应生成TiC颗粒(TiCp)和TiB晶须(TiBw)构成的非连续网状结构能有效细化晶粒,使晶粒粒径从118.8μm减小到33.1μm。GNPs和B的加入可以显著提高材料的维氏硬度,GNPs/TC4和(GNPs+B)/TC4复合材料的维氏硬度分别为3.91和4.15 GPa,相比于TC4钛合金(3.37 GPa)分别提高了16%和23%。GNPs/TC4和(GNPs+B)/TC4复合材料硬度的提升可以归因于晶界处的硬质颗粒(TiBw和TiCp)的存在。

GNP法制备固体氧化物燃料电池复合阳极材料Cu_xCo_(1-x)-SDC的研究

采用甘氨酸-硝酸盐法制备了CuxCo1-xO-SDC复合阳极材料。利用电化学工作站测试了其电化学性能,使用SEM、电导率、红外、差热-热重分析仪对CuxCo1-xO-SDC进行表征。研究结果表明,在Cu基阳极中加入一种具有高催化活性的金属钴,阳极表现出很好的催化活性,提高了电池的电化学性能。

La_(0.8)Ca_(0.2)CrO_3钙钛矿复合氧化物的GNP法合成与表征

采用GNP(Glycine-Nitrate Process)法合成La_(0.8)Ca_(0.2)CrO_3初级粉料,研究甘氨酸用量对产物的晶体结构和显微形貌的影响,并测试烧结体的相对密度和电导率。研究结果表明,甘氨酸与金属离子的摩尔比(G／M^(n+))控制在2.0～2.5时可得到颗粒尺寸细小、均匀(100nm～200nm)的单相钙钛矿粉体,烧结温度为1350℃时样品的相对密度达到91.0％,测试温度为800℃时样品的电导率达到30.5 S．cm^(-1)。与常规固相法相比,GNP法制备的样品具有更好的烧结活性和导电性能。

Effect of Process Parameters on the Agglomeration Behavior and Tensile Response of Graphene Reinforced Magnesium Matrix Composites Based on Molecular Dynamics Model

The mechanical properties of graphene reinforced composites are often hampered by challenges related to the dispersion and aggregation of graphene within the matrix.This paper explores the mechanism of cooling rate,process temperature,and process pressure’s influence on the agglomeration behavior of graphene and the tensile response of composites from a computer simulation technology,namely molecular dynamics.Our findings reveal that the cooling rate exerts minimal influence on the tensile response of composites.Conversely,processing temperature significantly affects the degree of graphene aggregation,with higher temperatures leading to the formation of larger-sized graphene clusters.In contrast,processing pressure exhibits negligible impact on the degree of graphene aggregation,and increasing pressure effectively mitigates the formation of large-sized graphene clusters.Moreover,we elucidate the intrinsic factors governing the mechanical response to variations in processing parameters.Notably,we observe that the stretching process facilitates the decomposition of large-sized graphene clusters into smaller ones.This research contributes to the advancement of lightweight metal matrix composites by offering insights into optimizing processing parameters.Additionally,it provides crucial theoretical underpinnings for developing high-performance graphene-reinforced composites.

Graphite Nanoplatelets Composite Materials: Role of the Epoxy-System in the Thermal Conductivity

Polymers typically have intrinsic thermal conductivity much lower than other materials. Enhancement of this property may be obtained by the addition of conductive fillers. In this research, epoxy nanocomposites with exfoliated graphite nanoplatelets are prepared and characterized. The chosen approach requires no surface treatment and no sophisticated equipments allowing one to produce composites on a pilot scale. A significant increase of the thermal conductivity with the increasing of the graphite fillers content is nevertheless observed on 4 mm thick specimens. Our results viewed in the latest scientific findings suggest that the choice of resin is an important parameter to move towards composite materials with high thermal conductivity.

Finite Element Prediction of the Thermal Conductivity of GNP/Al Composites

A 3 D multi-scale finite element model was developed to predict the effective thermal conductivity of graphene nanoplatelet(GNP)/Al composites.The factors influencing the effective thermal conductivity of the GNP/Al composites were investigated,including the orientation,shape,aspect ratio,configuration and volume fraction of GNPs.The results show that GNPs shape has a little influence on the thermal conductivity of GNP/Al composites,and composites with elliptic GNPs have the highest thermal conductivity.In addition,with increasing the aspect ratio of GNPs,the thermal conductivity of GNP/Al composites increases and finally tends to be stable.The GNPs configuration strongly influences the thermal conductivity of GNP/Al composites,and the thermal conductivity of the composites with layered GNPs is the highest among the five configurations.The effective thermal conductivity is sensitive to volume fraction of GNPs.Ideally,when the volume fraction of layered GNPs reaches 1.54%,the thermal conductivity of GNP/Al composites is as high as 400 W/m K.The findings of this study could provide a good theoretical basis for designing high thermal conductivity GNP/Al composites.

掺纳米石墨烯片的水泥基复合材料的压敏性

研究了掺入少量纳米石墨烯片(GnPs)的水泥基复合材料的力学性能、电学性能和压敏性,结果表明,GnPs的掺入显著提高了水泥砂浆的早龄期抗压强度,但对后期抗压强度的影响不大。GnPs表面积较大,将阻塞离子移动通路,故少量GnPs(体积掺量低于0.15%)对改善水泥砂浆导电性的作用效果不明显。GnPs水泥基复合材料能感知应力、应变,GnPs的掺入提高了其灵敏度和重复性。

纳米石墨烯片/石蜡复合相变蓄热材料的热性质研究

采用两步法,通过磁力搅拌和超声振荡,制备了以纳米石墨烯片GnPs为导热增强相的纳米GnPs/石蜡复合相变蓄热材料。红外光谱分析结果表明GnPs与石蜡之间未发生化学反应,仅是简单的物理复合作用。差示扫描量热分析(DSC)表明,复合材料的相变温度几乎保持不变,但其相变潜热随纳米GnPs含量的增加呈降低趋势,在质量分数为1%时,熔化和凝固过程的相变潜热较纯石蜡分别下降约9.6%和10.1%。此外,复合材料的导热系数随GnPs质量分数增加而增加,在质量分数为2%时,导热系数相对提高率为34.2%,表现出良好的强化导热效果。

石墨烯/铝复合材料热挤压过程组织演变

采用冷等静压后热挤压变形工艺制备高含量石墨烯增强6061Al复合材料,研究热挤压变形过程中复合材料显微组织的演化特征。结果表明：冷等静压后坯锭的致密度达到92.5%,在挤压温度480℃、挤压比25∶1的条件下,复合材料棒材的致密度达到99.7%。随着塑性变形量的增大,石墨烯团聚体逐渐被打散,并沿挤压方向呈不连续状分布;由于热挤压保温温度远低于热压烧结温度,热挤压态复合材料中石墨烯与铝合金未发生界面反应;冷等静压后进行高温塑性变形可获得高致密度的复合材料,同时避免了石墨烯与铝合金之间生成Al_4C_3的界面反应。

IT-SOFC复合阳极材料CDC-LSCMCo的制备及性能

采用甘氨酸-硝酸盐法(GNP法)一次性合成固体氧化物燃料电池复合阳极材料Ce0.8Ca0.2O2-La0.7Sr0.3Cr0.5Mn0.5-xCoxO3-δ(CDC-LSCMCo)。XRD、SEM和EDS分析结果表明:1350℃下烧结5h能够得到单一萤石-钙钛矿结构且粒度较小(1μm左右)的复合阳极粉体。电导率的测试研究发现,温度大于750℃时,电导率随Co含量的增加而增大。800℃时,CDC-LSCMCo0.15分别在空气与氢气气氛下的电导率分别为10.5和0.7S·cm-1。SEM和XRD分析表明:CDC-LSCMCo与La0.9Sr0.1Ga0.8Mg0.2O3-δ电解质材料有很好的热与化学相容性,是一种应用前景良好的IT-SOFC阳极材料。

轧制变形量对GNPs/Ti复合材料组织与性能的影响（英文）

采用放电等离子烧结技术(SPS)和热轧制备了石墨烯/钛基复合材料(GNPs/Ti)。重点研究了轧制变形量对GNPs/Ti复合材料的显微组织及力学性能的影响规律。采用扫描电镜观察不同变形量后的显微组织,结果显示,随着轧制变形量的增加,基体晶粒长径比增大,石墨烯取向性提高。拉伸结果表明,GNPs/Ti复合材料的抗拉强度和断后伸长率随着变形量的增加而增加,在变形60%时,最大抗拉强度达到680 MPa,相比纯钛提高了33%。采用轧制工艺可以使GNPs/Ti复合材料孔洞减少、GNPs分布具有取向性,从而提高材料的力学性能。

石墨烯增强镁合金塑性加工的组织和力学性能

为获得优异力学性能的复合材料,选用石墨烯作为增强体.本文采用粉末冶金方法,经高能球磨法、冷压、烧结、热压和热挤压制备了AZ31镁合金及石墨烯(GNPs)增强AZ31镁基复合材料棒状试样,通过光学显微镜(OM)、扫描电子显微镜(SEM)、X射线衍射(XRD)和室温拉伸、压缩表征了该材料的组织和力学性能.结果表明:制备的复合材料及基体中生成了Mg_(17)Al_(12)和MgO,加入GNPs后复合材料的屈服强度与维氏硬度都优于基体材料;加入GNPs质量分数为0.5%和1.0%的GNPs复合材料分别比基体屈服强度增加13.2%和14.2%(258和259 MPa),显微维氏硬度分别增加11.4%和14.3%(78和80 HV),主要的强化机制为载荷转移强化、奥罗万强化、热错配强化,但材料的拉伸延伸率分别降低到3.9%和4.3%,比基体分别降低了38%和32%,材料的致密度分别为99.6%、98.5%、97.8%,随着GNPs的增加,致密度降低;GNPs的加入未改变材料的断裂方式,材料的断裂方式均主要为脆性断裂;GNPs的添加使复合材料的基面{0002}织构弱化,从而降低材料的屈服不对称性.

石墨烯纳米片增强ODS钢复合材料的制备及其拉伸性能

为了提高ODS FeCrAl合金的机械性能和导热性能,采用机械合金化法将石墨烯纳米片(GNPs)和ODS FeCrAl粉末进行混合,并利用放电等离子烧结(SPS)技术制备GNPs/ODS FeCrAl复合材料。利用扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电镜(TEM)、电子万能试验机和热盘法(hot-disk法)等分析混合粉末混合前后的形貌,研究石墨烯添加对烧结态复合材料微观结构、拉伸性能和导热性能的影响。研究结果表明:在混合粉体中未检测到碳化物,而烧结态复合材料中发现了少量CrC和CrC,这表明在固结过程中部分石墨烯与基体中Cr元素发生了反应。经过高能球磨后,部分石墨烯纳米片被镶嵌在ODS钢粉末中,而其他石墨烯纳米片则保持其固有结构。烧结态GNPs/ODS钢复合材料的抗拉强度和导热系数分别达到了1 078 MPa和10.88 W/(m·K),相比未添加石墨烯的ODS钢,分别提高了18%和22%。