Synthesis and characterization of TiC-reinforced iron-based composites Part I On synthesis and microstructural characterization

The present investigation establishes a liquid processing route where thermit based reactions have been used to synthesize in-situ TiC-reinforced Fe-based composites in a single step. The main raw material used is siliceous sand, which is a waste product of aluminum extraction plants. A dispersion of TiC in Fe-based matrix has been obtained by aluminothermic reduction of siliceous sand, containing oxides of different elements like iron, titanium, silicon etc., in the presence of carbon. The reduction is highly exothermic in nature and leads to a self-propagating high-temperature synthesis (SHS) of the Fe-TiC composites. The matrix structure and volume fraction of TiC of the composites have been found to depend upon the amount of carbon added in the charge. It has been found that microstructures of Fe-TiC composites are not stable at high temperature due to the nonstoichiometric nature of TiC particles.     

Effect of form of carbon on the microstructure of in situ synthesized TiC-reinforced iron-based composite

TiC-reinforced iron-based composites were synthesized by aluminothermic reduction of siliceous sand (a waste product of aluminium extraction plant containing oxides of Fe, Ti, Si, etc.) in the presence of carbon. The carbon was used either in the form of only graphite, mostly cast iron or graphite plus cast iron. Results show that the microstructure as well as the volume fraction of TiC strongly depends upon the form of carbon.     

Carbon nanotube yarn and 3-D braid composites. Part II: Dynamic mechanical analysis

Macroscopic textile preforms were produced with a multi-level hierarchical carbon nanotube (CNT) structure: nanotubes, bundles, spun single yarns, plied yarns and 3-D braids. In tensile tests, reported in Part I, composites produced from the 3-D braids exhibited unusual mechanical behavior effects. The proposed physical hypotheses explained those effects by molecular level interactions and molecular hindrance of the epoxy chains with individual carbon nanotubes occupying about 40% of the composite volume. Dynamic mechanical analysis was used in this Part II to study the molecular transitions of neat epoxy resin samples and their corresponding CNT yarn composite samples with varying matrix properties. Dramatic effects on the intensity and temperature at which α-transitions occured, were recorded, as well as a marked effect on the smaller segmental motions, or β-transitions. These changes in the matrix assist in explaining the mechanical test data presented in Part I and the proposed physical explanation of those data.     

Synthesis and mechanical characterization of polymer-matrix composites containing calcium carbonate/white cement filler

With a view to develop polymer-matrix composites of high mechanical strength, composites containing 0.5% to 5.0% of each of calcium carbonate or white cement were prepared by uniformly mixing polystyrene and inorganic materials followed by casting in an aluminum mold. The values of fracture toughness, flexural strength and elastic modulus were found to increase with increasing amount of the inorganic component in the polymer. In addition, for a given percentage of inorganic components, the values of mechanical strength of white cement containing composites were found to be more than those of calcium carbonate containing composites. The optical microphotographs of the composites show that there is uniform distribution of filler in the polymers.     

Processing and mechanical characterization of lightweight polyurethane composites

A simple procedure was established to fabricate polyurethane-cenosphere particulate composite materials. Composites having four different volume fractions of cenospheres (hollow ceramic microspheres) ranging from 10 to 40% in increments of 10% were prepared and their mechanical properties were evaluated. A predictive model to estimate the fracture toughness of the composite was developed. The dynamic constitutive behavior of the composite in compression was investigated using the split Hopkinson pressure bar (SHPB) technique in conjunction with high-speed photography. The results of the material characterization indicated that addition of cenospheres decreased the density of the composite. The quasi-static stiffness, both in tension and compression, and the quasi-static fracture toughness of the composite increased with addition of cenospheres. The high strain rate constitutive behavior of 100% polyurethane showed monotonic stiffening whereas the composite at higher cenosphere volume fractions (40%) exhibited a stiffening-softening-stiffening behavior. Scanning Electron Microscopy (SEM) studies were also carried out to determine the failure mechanisms of the composite.     

Synthesis and mechanical properties of niobium aluminide-based composites

Niobium aluminide-based composites reinforced with in situ and externally added Al₂O₃ and TiC particulates were fabricated by hot-pressed sintering at 1400 °C. In particular, Nb₂Al–Al₂O₃–TiC in situ composites were successfully obtained from the raw powder mixtures of Nb60Al40 (in at.%)–TiO₂20C8 (in wt.%) by means of this process. The influences of ceramic particulates on the microstructures, flexural strength and fracture toughness were examined. The experimental results indicate that the presence of ceramic particulates yielded a remarkable improvement in both the strength and fracture toughness in comparison with previous results for monolithic niobium aluminide compounds.     

Synthesis and characterization of polyaniline rubber composites

Composite films of polyaniline and synthetic rubber (cis-1,4-polyisoprene) were studied to understand the charge transport under pressure and temperature. Films of different compositions were prepared to measure current–voltage curves across the film thickness. The results reveal that these materials exhibit electrical conductivity as predicted by the classical theory of percolation. This has been discussed in the light of microscopic interaction between rubber and polyaniline aggregates. Pressure dependent electrical conductivity of these composites can be best explored to develop low cost pressure sensing materials.     

Elaboration and mechanical characterization of multi-phase alumina-based ultra-fine composites

Al₂O₃-10 vol.% YAG and Al₂O₃-10 vol.% ZrO₂ bi-phase composites as well as Al₂O₃-5 vol.% YAG-5 vol.% ZrO₂ tri-phase composite were developed by controlled surface modification of an alumina powder with inorganic precursors of the second phases. Green bodies were produced by dry pressing and slip casting and then sintered at 1500 °C. In particular, slip casting led to fully dense, defect-free, and highly homogenous samples, made of a fine dispersion of the second phases into the micronic alumina matrix, as observed by SEM. The mechanical characterization proved the predominant role of the final density on the Vickers hardness, while the elastic modulus was affected by the volume fraction of the constituent phases, in fairly good agreement with the rule of mixture prediction. The fracture toughness values of the bi- and tri-phase materials were similar, and their crack paths revealed the importance of the thermal residual stresses at the matrix-reinforcement interfaces, promoting inter-granular propagations.     

Fabrication,characterization and mechanical properties of SiC-whisker-reinforced Y-TZP composites

The microstructure and mechanical properties of hot-pressed yttria-stablized tetragonal zirconia polycrystals (Y-TZP) reinforced with up to 30 vol % SiC whiskers were investigated. The homogeneously dispersed and fully dense SiC whisker/Y-TZP composites were fabricated by wet-mixing the constitutents and uniaxially hot-pressing the resulting powder. The grain size of the matrix depended on the whisker volume fraction and the hot-pressing temperature. The significant increase of fracture toughness of about MPa m^1/2 at 10 Vol % SiC and a small increase in strength were achieved by uniformly dispersing the whiskers in the Y-TZP matrix. Fracture surfaces revealed evidence of toughening by the mechanisms of crack deflection, pullout, and crack bridging by the whiskers and also a phase transformation of ZrO₂. The observed increase in the fracture toughness of Y-TZP due to the addition of SiC whiskers was correlated with existing models of toughening mechanisms. Good agreement was achieved between the theoretical predictions and the experimental toughness values, obtained from the Y-TZP/SiC_w composites.     

Synthesis, characterization and mechanical properties of nano alumina particulate reinforced magnesium based bulk metallic glass composites

Mg₆₇Zn₂₈Ca₅ bulk metallic glass reinforced with 0.66-1.5 vol% of nano alumina particulates were successfully synthesized using disintegrated melt deposition technique. Microstructural characterization revealed reasonably uniform distribution of alumina particulates in a metallic glass matrix. The reinforced particles have no significant effect on the glass forming ability of the monolithic glass matrix. Mechanical characterization under compressive loading showed improved micro hardness, fracture strength and failure strain with increase in nano alumina particulate reinforcement. The best combination of strength, hardness and ductility was observed in Mg/1.5 vol% alumina composite with fracture strength of 780 MPa and 2.6% failure strain.     

Impact characterization of RTM composites: Part I Metrics

The use of textile based architectures and the dry compaction of preform layers prior to resin infusion creates the potential for highly tailored resin transfer-moulded composites that have significantly different response to impact than traditional prepreg-based composites. The response of a number of resin transfer moulding (RTM) composites is characterized using both traditional and new metrics of performance. Impact performance maps are used to differentiate between materials response at a fundamental level and key differences are traced to differences in preform fabric architecture. Global and local differences in response based on architecture are elucidated through the determination of damage and energy absorbance, and are related to materials' specific characteristics in an attempt to allow comparison of impact response of composites on a more quantitative basis. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis,characterization and mechanical behavior of Al 3003 - TiO2 surface composites through friction stir processing

Aluminum 3003 alloy used in the gas turbine and aerospace applications possesses medium bearing capacity. This technical paper reports the fabrication of Al 3003 alloy/TiO₂ composites using friction stir processing. The weight fraction of reinforced TiO₂ particles is varied between 0% and 6% with the increment of 1.5% in sequence. The fabricated specimens have been characterized by optical microscopy (OM), Energy dispersive X-ray spectroscopy (EDAX), Field emission scanning electron microscopy (FESEM), X-ray Diffraction analysis (XRD) and electron backscattered diagram (EBSD). Composite weld zone has witnessed the homogeneous distribution of TiO₂ particles. The formation of such composite by reinforcement exhibits increase in the hardness and tensile strength of the weld. Corresponding strengthening mechanism is illustrated and correlated with the characterization studies. Fractography study shows brittle to ductile transformation with the addition of TiO₂ particles.     

Synthesis and characterization of new polyaniline/nanotube composites

New polyaniline/nanotube (PANI/NT) composites have been synthesized by “in situ” polymerization processes using both multi-wall carbon nanotubes (MWNTs) and single-wall carbon nanotubes (SWNTs) in concentrations ranging from 2 to 50 wt.%. Although no structural changes are observed using MWNTs above a concentration of 20 wt.%, the in situ synthesis results in electronic interactions between nanotubes and the quinoid ring of PANI leading to enhanced electronic properties and thus to the formation of a genuine PANI/MWNT composite material. On the other hand, using SWNTs favors the formation of inhomogeneous mixtures rather than of a homogeneous composite materials, independent of the SWNT concentration. X-ray diffraction, Raman and transport measurements show the different behavior of both classes of nanotubes in PANI/NT materials. The difficulties in the formation of a true PANI/SWNT composite are related to the far more complex structure of the SWNT material itself, i.e. to the presence of entangled bundles of SWNTs, amorphous carbon and even catalytic metal particles.     

Synthesis and characterization of nano-HA/PA66 composites

Based on the bioactivity and biocompatibility of hydroxyapatite (HA) and the excellent mechanical performance of polyamide 66 (PA66), a composite of nanograde HA with PA66 was designed and fabricated to mimic the structure of biological bone which exhibits a composite of nanograde apatite crystals and natural polymer. The HA/PA66 composite combines the bioactivity of HA and the mechanical property of PA66. This study focused on the preparation method of HA/PA66 composite and the influence of HA crystals on the characterization of the composite. HA slurry was used directly to prepare HA/PA66 composite by a solution method, in which HA is able to form hydrogen bond, i.e. chemical bonding with PA66. The nano-HA needle-like crystals treated by hydrothermal method are better in the particle size distribution and the particle dispersion. The morphology, crystal structure and crystallinity as well as crystal size of these needle-like crystals are similar to bone apatite. The nano-HA needle-like crystals dispersed uniformly in PA66 matrix with reinforcement effect and can prevent the micro-crackle spreading into cleft and fracture during the deformation process. The mechanical testing shows that the nano-HA/PA66 composite has a good mechanical property, and may be a promising bone replacement material.     

Behaviour of photopolymerized silicate glass fibre-reinforced dimethacrylate composites subjected to hydrothermal ageing Part II Hydrolytic stability of mechanical properties

The flexural properties and failure morphologies of dimethacrylate-copolymer composites reinforced with either S2-glass® or quartz fibres (33–66 vol%) were examined after hydrothermal ageing (0–3 mon at 37 °C). Initially the S2-glass® composites were generally stiffer and stronger than comparably reinforced quartz composites, but within 1 wk the properties of S2-glass® composites decreased by 12%–26%. The properties ofquartz composites were relatively stable, except for those of composites with the least reinforcement (35 vol%), which decreased by roughly 15%. Scanning electron microscopy revealed that in all composites buckling had occurred at the site of load application. Evidence of good fibre–matrix adhesion was observed for both types of composites under all conditions. Modelling of degradation between 1 wk and 3 mon revealed that: (1) the only temporal change was a slight increase in the stiffness of S2-glass® composites; and (2) higher reinforcement levels reduced the retention of strength in S2-glass® composites but had the opposite effect (on both properties) for quartz composites (p<0.05). For the most highly reinforced S2-glass® composites, susceptibility to degradation was offset by high initial properties; and after ageing (elastic modulus 50 GPa, strength 1.2 GPa), these composites were still, on average, approximately 25% stiffer and 50% stronger than the more hydrostable quartz counterparts. © 1998 Kluwer Academic Publishers     

聚丙烯/海泡石复合材料的制备、表征及力学性能

采用十六烷基三甲基溴化铵(CTAB)对海泡石(SEP)进行有机化改性,制备有机改性海泡石(OSEP)和聚丙烯(PP)/SEP复合材料。经SEM、XRD、FT-IR、TG和CA分析,表明海泡石表面吸附有一定量的季铵盐分子,并且部分季铵盐分子顺利进入海泡石孔道。经TG分析,800℃时OSEP的残留质量比SEP提高17.63%。复合材料的拉伸、冲击和WAXD测试表明,OSEP的加入减少了β晶型的含量,增加了α晶粒的含量,有效提高了复合材料的力学性能。当OSEP含量为1.5%时,能获得力学性能较优的复合材料。     

Influence of heat treatment on microstructure and mechanical properties of iron-based coating

Iron-based alloys were deposited on the low carbon steel by plasma cladding process. Furnace annealing was conducted at 600 °C for 40 min. Resulting microstructure and phases were observed and investigated by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD). Effect of post heat treatment on the mechanical properties of coatings was also studied by instrumented indentation technique. It was found that solid solution γ-(Fe, Ni, Cr) and carbide reinforced phases Cr₇C₃ were the main phases of as-cladding coatings while iron carbide became the main carbide reinforced phase for annealed coatings. For all coatings, hardness and reduced elastic modulus showed obvious load dependence, namely decreased with the indentation load increasing. It was found that calculated values of annealed coatings were generally lower than those of as-cladding coatings as a result of the dissolution of the eutectic structure which decreased the effect of dispersion strengthening.     

可反应性纳米SiO2/尼龙1010复合材料的制备和力学性能

以可反应性纳米SiO2(RNS)为填料,用熔融共混法制备SiO2/尼龙1010纳米复合材料,表征其力学性能并研究了增强和增韧机理.结果表明,在熔融共混过程中RNS与尼龙1010发生了强烈的界面相互作用,提高了材料的拉伸强度、断裂伸长率和弹性模量;而纳米SiO2的表面有机修饰层使材料的韧性有所提高.纳米SiO2质量分数为1.0%的复合材料拉伸强度最大,比纯尼龙1010的高4%;而0.7%纳米SiO2的复合材料断裂伸长率和弹性模量最大,分别比纯尼龙的高16.6%和13.4%.