Structure and properties of boron/aluminium composites

The influence of heat treatment on the structure and strength of boron/aluminium composites has been studied. Matrix material around a fibre is assumed to be hardened by dispersed particles of boron-containing compounds, presumably magnesium borides. Such a material is expected to have higher yield strength and greater brittleness compared to the original matrix material. A fibre and its surrounding zone is a prospective site of microcracking under loading. These zones grow as heat treatment proceeds. When neighbouring zones become linked to each other, the size of a possible brittle microcrack is doubled and a fall in the composite strength follows. A corresponding microstructural model of the composite failure is constructed.

Without having direct observation of magnesium borides, the model of composite behaviour is supported by (i) dependence of the composite strength on the size of the influence zone; (ii) dependence of the strength on the effective time, the latter being determined by the activation energy of magnesium diffusion in aluminium; (iii) observation of failure surfaces of composites subjected to various heat treatments; and (iv) a correlation of changes of matrix state detected by changes in X-ray diffraction patterns with a hypothetical picture of the development of the influence zones.     

Dielectric properties of carbon black: SBR composites

A series of styrene–butadiene rubber (SBR) composites have been prepared with different weight ratios of polyacetylene based conducting carbon black (CCB) (0–90 phr). The SBR–CCB systems are characterized for dimensional stability which is enhanced by increasing the CCB loading because of enhancement in polymer-filler interaction. The electrical properties such as dielectric constant (ε_r), dissipation factor (tan δ) and dielectric loss (ε″) of the composites have been studied. The influence of different loading of CCB (0–90 phr), frequency of ac (100 Hz–30 MHz) and temperature (25–75 °C) on the electrical properties was studied. An increase in dielectric constant and tan δ of the SBR composites was observed with increase in CCB content and ac frequency. This is due to enhancement of filler–filler interaction and the increase in continuity of conducting phase. The surface morphology has been studied using scanning electron microscopy (SEM).     

电纺PLLA/PCL/PEG共混纤维膜的结构及性能

采用静电纺丝技术制备了聚乳酸（PLLA）/聚己内酯（PCL）/聚乙二醇（PEG）共混纤维膜,考察了溶剂体积比、共混物共混质量比、溶液浓度对电纺纤维形貌的影响,研究了共混纤维膜的热稳定性、结晶性、力学性能及亲水性。结果表明加入PEG有效提高了共混纤维膜的热稳定性和结晶性,提高了共混纤维膜的拉伸强度、弹性模量和亲水性能。     

无压渗透法制备Al／AlN复合材料及其性能

在常压下通过熔渗工艺将AlSi7Mg合金渗入由AlN粉末模压成形、预烧所获得的预烧结坯中,得到了不同Al含量的Al／AlN复合材料。采用X射线衍射仪对复合材料的相组成进行了测试,采用金相显微镜和SEM对其显微组织进行了观测,并对不同Al含量的Al／AlN复合材料的维氏硬度、抗弯强度、热膨胀系数及导热系数等进行了测试分析...     

EVA-g-PU/SBR/OMMT复合材料的制备与性能表征

采用熔融共混与熔融插层相结合的方法,制备了EVA-g-PU/SBR/OMMT复合材料.采用x-射线衍射仪(XRD)与透射电镜(TEM)研究了蒙脱土在聚合物基体中的分散状态,用电子万能试验机、摩擦磨损试验机测试了材料的力学性能及耐摩擦磨损性能,并通过扫面电镜分析了材料的磨损机理.结果表明,蒙脱土主要以插层型分布在聚合物基...     

Structure and mechanical properties of nanocrystalline Ag/MgO composites

Nanocrystalline Ag/MgO composites were prepared by the ultrafine-powder-compaction method. The structure was investigated for the first time by high-resolution electron microscopy. Nanometre-sized Ag grains and MgO grains in the composites bonded directly without any intermediate phase layer. Certain preferred orientation relationships were observed between the Ag and MgO grains. The nanocrystalline Ag/MgO composites retained their grain size during annealing up to 873 K. Vickers microhardness measurements were performed on the as-compacted and annealed specimens. Generation and propagation of cracks were less active in the nanocrystalline Ag/MgO composites than in a single-phase nanocrystalline MgO. The Vickers microhardness of the nanocrystalline Ag/MgO composites remained up to 1073 K. Hot-pressing deformation tests showed that the nanocrystalline Ag/MgO composites deformed plastically at 1073 K.     

C/C-SiC复合材料模压成型工艺与性能研究

利用碳纤维编织布为增强体,采用混合粉料模压成型工艺制备C/C-SiC复合材料,分析了各个因素对C/C-SiC复合材料密度及强度影响的大小以及显著性。研究表明,树脂与石墨粉比例和纤维含量对C/C-SiC复合材料密度的影响比较大,而硅粉含量以及配比浓度的影响较小且基本相同;同时树脂与石墨粉比例这一因素对C/C-SiC复合材料强度影响也非常显著。并且随着树脂含量的减少,C/C-SiC复合材料强度降低。     

甲基硅酸盐/硅酸盐复合膜的组成和性能研究

采用两步法制备甲基硅酸盐/硅酸盐复合膜,通过扫描电子显微镜(SEM)及EDS分析、红外光谱(FT-IR)分析、接触角测试、中性盐雾实验和极化曲线等对膜层的微观形貌、化学组成、疏水性及耐腐蚀性能进行了研究,并与单独的硅酸盐膜、甲基硅酸盐膜进行对比.利用电化学阻抗谱和等效电路拟合分析甲基硅酸盐/硅酸盐复合膜的防腐蚀机理.结果表明:甲基硅酸盐/硅酸盐复合膜层的外层与单独甲基硅酸钠膜的成分含量基本一致,但其微观形貌与单独甲基硅酸盐膜表面布满裂纹不同,复合膜层的表面均匀平整、没有开裂,膜层附着性好.单独硅酸盐膜为亲水性膜层,甲基硅酸盐/硅酸盐复合膜表现出疏水性,与单独硅酸盐膜相比,复合膜对腐蚀的阴极过程的抑制明显增强,极化阻抗增加至单独硅酸盐膜的5倍以上,复合膜的总阻抗值超过100 kΩ·cm2,复合膜的腐蚀电流密度比单独硅酸盐膜的降低了60％.     

Structure and tensile properties of polypropylene/carbon nanotubes composites prepared by melt extrusion

Polypropylene/carbon nanotubes (PP/CNTs) nancomposites were prepared with a single screw extruder by adding maleic anhydride-grafted poplypropylene (PP-g-MAH) as compatibilizer to polypropylene (PP) with different amounts of carbon nanotubes (CNTs) in the range of 0.1–0.7 wt.%. Structure and morphology of the prepared samples were examined by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), polarizing light microscopy (PLM) and X-ray diffraction (XRD). The results showed that PP spherulites decreased in size when CNTs were introduced into the polymer. Mechanical properties of the samples were also studied. Tensile tests showed that with increasing amount of CNTs the strain at break decreased whereas the Young’s modulus was improved of 16.41 % to 36.05 % and tensile strength of 36.67 % to 64.70 % compared to pristine PP. The SEM microphotographs showed that majority of the CNTs were dispersed individually and oriented along the shear flow direction.     

Structure and mechanical properties of mechanically alloyed Al/Al-Cu-Fe composites

Quasicrystalline (QC) powder was prepared by mechanical alloying and subsequent annealing of Al₆₅Cu₂₃Fe₁₂ composition. Obtained quasicrystals were milled together with pure aluminium in the ratios of Al-20 wt% QC and Al-10 wt% QC. A hot consolidation of samples was performed under pressure of 4.5 GPa at elevated temperatures. X-ray diffraction study of the as-consolidated samples shows that the quasicrystalline phase remained in the samples if consolidation temperature was lower than 500°C. Consolidation at higher temperatures results in disappearing of the QC and formation of crystalline phases, such as Al₂Cu and Al₇Cu₂Fe by reaction between QC and aluminium matrix. SEM study of microstructure of the composite alloys shows an absence of open porosity in the consolidated bulk samples. Besides rather large particles of reinforcing phase of about 20 μm there are also very small particles of less than 1 μm. The uniformity of particles distribution in the matrix increases with increase in the milling duration. Microhadrness measurements and compression tests were performed, an effect of the treatment parameters on the compressive strength was studied.     

聚丙烯/镁盐晶须复合材料的形态结构与性能研究

采用哈克单螺杆挤出机制备了聚丙烯/镁盐晶须复合材料,着重研究了增容剂聚丙烯接枝马来酸酐（PP-g-MAH）对复合材料的晶体结构与球晶形态、结晶和熔融行为、热稳定性以及力学性能的影响。研究表明镁盐晶须具有明显的诱导β-晶型的异相成核作用,使聚丙烯结晶温度大幅度提高,球晶尺寸细化。增容剂的加入改善了树脂与晶须的界面性能,界面粘结作用明显增强,提高了拉伸强度和冲击性能,并进一步提高了结晶温度和晶须的成核能力,但降低了β-晶型的含量,不利于β-晶型的生成。     

Mechanical properties investigation of carbon/carbon composites fabricated by a fast densification process

Carbon/carbon (C/C) composites were prepared by thermal gradient chemical vapor infiltration with a fast densification rate. The fracture morphology and mechanical properties were examined by scanning electron microscopy and mechanical testing, respectively. The effects of preform type and heat treatment temperature (HTT) on the mechanical properties of C/C composites were analyzed. The results show that the average flexural strength drops from 47.8 MPa to 38.6 MPa as the HTT increases from 2100 °C to 2500 °C. C/C composites with felt as preform show brittle fracture and samples with needle-punched felt as reinforcement present obvious pseudoplastic property. The interlaminar shear strength of needle-punched felt reinforced composites is higher than that of sample with felt as preform by 44.26% owing to the needle-punched fiber in the thickness direction. The strength of interfacial bonding plays a key role to mechanical properties and failure behavior of C/C composites.     

Structure and properties of refractory compounds deposited by direct evaporation

This paper reports on the structure and properties of refractory compound deposits of TiB₂, ZrB₂, ZrC, 55% TiB₂?45% ZrB₂ and 60% ZrC?40% ZrB₂. The deposits were prepared by direct evaporation of TiB₂, ZrB₂ and ZrC from water- cooled copper crucibles using an electron beam as the heat source. The vapors were condensed on a Mo substrate which had a temperature gradient ranging from 650°C to 1600°C. The deposition rate was 1–3 μm min^-1, and the thickness ranged from 25 to 75 μm.The deposits were characterized by optical and scanning electron microscopy, X-ray diffraction analysis, energy-dispersive analysis and microhardness determinations.     

Structure and mechanical properties of polyethylene-fullerene composites

The microhardness of films of fullerene-polyethylene composites prepared by gelation from semidilute solution, using ultrahigh molecular weight polyethylene (PE) (6×10⁶), has been determined. The composite materials were characterized by optical microscopy and X-ray diffraction techniques. The microhardness of the films is shown to increase notably with the concentration of fullerene particles within the films. In addition, a substantial hardening of the composites is obtained after annealing the materials at high temperatures (T _a=130 °C) and long annealing times (t _a=10⁵s). The hardening of the composites with annealing temperature has been identified with the thickening of the PE crystalline lamellae. Comparison of X-ray scattering data and the microhardness values upon annealing leads to the conclusion of phase separation of C₆₀ molecules from the polyethylene crystals within the material. The temperature dependence is discussed in terms of the independent contribution of the PE matrix of the C₆₀ aggregates to the hardness value.     

Effect of blend composition on the morphology and mechanical properties of microfibrillar composites

Various blend compositions of polyethyleneterphthalate (PET) and polyamide 6 (PA 6) were used to prepare microfibrillar composites (MFC's) in form of thin ribbons. Steps for preparation were: (1) blending, (2) extrusion, (3) fibrillation, and (4) isotropization. The latter step was performed at a temperature condition above the melting temperature of PA 6, but below that of PET. In this way PET microfibrils remained as reinforcing elements in the PA 6-matrix. Depending on the actual PET/PA 6 ratio, various fibril arrangements in terms of fibril length and uniformity of fibril distribution could be achieved. A reasonable improvement in mechanical properties was reached already at 30 wt. % PET in PA 6 which was in terms of tensile strength higher than a 30 wt. % short glass fiber filled PA 6 system.     

PU/PVDF共混中空纤维膜结构与性能

采用熔体纺丝后拉伸的方法制备了聚氨酯(PU)/聚偏氟乙烯(PVDF)共混中空纤维膜,研究了拉伸对共混膜形态结构的影响,通过测定水通量随透膜压力的变化讨论了PU/PVDF共混中空纤维膜的压力响应性能,并对不同拉伸倍数所得膜压力响应性能差异进行了研究.结果表明,拉伸过程增大了聚合物间界面微孔的通透性,有效地提高了膜的水通量;且随拉伸倍数的提高,PU/PVDF共混中空纤维膜界面微孔的回复性有所提高.     

Structure and properties of highly oriented polyoxymethylene/multi-walled carbon nanotube composites produced by hot stretching

Highly-oriented polyoxymethylene (POM)/multi-walled carbon nanotube (MWCNT) composites were fabricated through solid hot stretching technology. With the draw ratio as high as 900%, the oriented composites exhibited much improved thermal conductivity and mechanical properties along the stretching direction compared with that of the isotropic samples before drawing. The thermal conductivity of the composite with 11.6 vol.% MWCNTs can reach as high as 1.2 W/m K after drawing. Microstructure observation demonstrated that the POM matrix had an ordered fibrillar bundle structure and MWCNTs in the composite tended to align parallel to the stretching direction. Wide-angle X-ray diffraction results showed that the crystal axis of the POM matrix was preferentially oriented perpendicular to the draw direction, while MWCNTs were preferentially oriented parallel to the draw direction. The strong interaction between the POM matrix and the MWCNTs hindered the orientation movement of molecules of POM, but induced the orientation movement of MWCNTs.