Microstructure effect on mechanical properties of in situ synthesized titanium matrix composites reinforced with TiB and La2O3

High temperature titanium matrix composites (TMCs) with different volume fraction of reinforcements were insitu synthesized by casting and hot forging. An effort was made to investigate the mechanical properties as a function of the microstructure of composites. Tensile tests were performed at room temperature, 600 °C, 650 °C and 700 °C respectively. Creep behavior at 650 °C was characterized in the stress range of 200-300 MPa. Results indicated that the composite with 2.11 vol.% reinforcements had the highest tensile strength and lowest steady state creep rate. Morphology of TiB whiskers was critical to mechanical properties of TMCs. TiB whiskers fracture and debonding acted as the dominant failure modes.     

Effects of ferrous ions on the reductive dechlorination of trichloroethylene by zero-valent iron

The surface characteristics of zero-valent iron (ZVI) and the efficiency of reductive dechlorination of trichloroethylene (TCE) in the presence of ferrous ions were studied. The experimental results indicated that the acid-washing of a metallic iron sample enhanced the efficiency of TCE degradation by ZVI. This occurred because acid-washing changed the conformation of oxides on the surface of iron from maghemite (gamma-Fe(2)O(3)) to the more hydrated goethite (alpha-FeOOH), as was confirmed by XPS analysis. However, when ferrous ions were simultaneous with TCE in water, the TCE degradation rate decreased as the concentration of ferrous ion increased. This was due to the formation of passive precipitates of ferrous hydroxide, including maghemite and magnetite (Fe(3)O(4)), that coated on the surface of acid-washed ZVI, which as a result inhibited the electron transfer and catalytic hydrogenation mechanisms. On the other hand, in an Fe(0)-TCE system without the acid-washing pretreatment of ZVI, ferrous ions were adsorbed into the maghemite lattice which was then converted to semiconductive magnetite. Thus, the electrons were transferred from the iron surface and passed through the precipitates, allowing for the reductive dechlorination of TCE.     

Microstructure evolution and oxidation behaviour of Tif/TiAl3 composites

In this paper, Ti_f/TiAl₃ composites were fabricated by infiltration–in situ reaction method and its oxidation behaviours were investigated by cyclic oxidation testing at 700 °C, 800 °C and 900 °C. The microstructure evolution and oxidation of Ti_f/TiAl₃ composites were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray diffraction (EDX). The reaction between Ti₃Al particles and Al was more violent than that of Ti fibres and Al. Ti₃Al/Al reaction consumed a large amount of Al and inhibited the reaction of Ti fibres indirectly. Reactant of Ti fibres was TiAl₃ at 700 °C, and four reaction layers surrounding Ti fibre (Ti₃Al, TiAl, TiAl₂ and TiAl₃ from inner to outside) were observed above 800 °C. The thickness of the total reaction layers increased little with temperature and time, while the thickness of inner reaction layers increased remarkably. A model corresponding to the microstructure evolution process was drawn schematically. Oxidation resistance of Ti_f/TiAl₃ composites decreased with increasing of temperature, and changed from cubic law at 700 °C to parabolic law at 900 °C. The oxidation weight gain of Ti_f/TiAl₃ composite was dominated by the exposed Ti fibres. Due to outward diffusion of Ti and Al element, the oxide of Ti fibre at 900 °C changed to mushroom-shape. Fortunately, when TiAl₃ was oxidized, a thin and continuous Al₂O₃ layer was formed, protecting matrix from further oxidation.     

The effect of temperature on toluene sorption by granular activated carbon and its use in permeable reactive barriers in cold regions

Granular activated carbon (GAC) has been used as an adsorbent for hydrocarbons in a range of permeable reactive barriers. This work investigates the influence of temperature on adsorption performance. In particular, the influence of temperature in the range of 20 °C to 4 °C on the sorption equilibrium and kinetics of toluene on GAC surface were investigated. The results show that low temperature leads to decreased toluene sorption by GAC and slower reaction kinetics. Sorption kinetics studies show that diffusion coefficients are also lower at 4 °C (3.65 × 10⁻¹³ m² s⁻¹) than 20 °C (5.112 × 10⁻¹³ m² s⁻¹).     

Low temperature extrusion of 6061 aluminum matrix composite reinforced with SnO2-coated Al18B4O33 whisker

The 6061 aluminum matrix composite reinforced with SnO₂-coated Al₁₈B₄O₃₃ whisker was fabricated by squeeze casting and following by extrusion extruded at elevated temperatures from 300 °C to 400 °C. Optimization of the extruding process, microstructure, texture and mechanical properties of the extruded composites were investigated. The lowest extrusion temperature at which a composite rod with high surface quality was successfully produced was 300 °C. The yield strength of composites is much improved after extrusion, and especially their elongation is increased by 300%. Such big improvements depend on a fact that SnO₂ coating can introduce low-melting-point Sn phase into the interface through an interfacial reaction. The melting of interphase and their surrounding areas is the main reason for the excellent extrusion ability of the composite. Besides, detailed X-ray diffraction analysis of the extruded composite textures reveals the significant effects of extrusion temperatures on their features.     

Direct patterning of SnO2 composite films prepared with various contents of Pt nanoparticles by photochemical metal-organic deposition

The optical and electrical characteristics of SnO₂ composite films with various contents (0, 0.05, 0.1, 0.2, and 0.3 at.%) of Pt nanoparticles were evaluated. The Pt nanoparticles were synthesized by a methanol reduction method and their average size was controlled to 3 nm using poly(N-vinyl-2-pyrrolidone) as a protecting agent. The lowest resistivity of 2.031 × 10^− 2 Ω cm was obtained in the SnO₂ film containing 0.2 at.% Pt nanoparticles after annealing at 700 °C while its average transmittance in the visible region was 85.24%. The enhanced electrical properties were attributed to the increase of the carrier concentration and crystallinity of the films due to donation from Pt nanoparticles as well as the increased annealing temperature. Meanwhile, the slight degradation of the transmittance was due to scattering from the introduction of Pt nanoparticles and the increased crystallite size due to the increase of the annealing temperature to 700 °C. Well-defined 20-μm wide direct-patterned composite SnO₂ films containing Pt nanoparticles were formed by a simple photochemical metal-organic deposition process involving a photosensitive starting precursor, UV exposure, and removal of the unpatterned area by rinsing with solvent. Based on the results of this study, we suggest that direct-patternable SnO₂ films with Pt nanoparticles can be easily applied to transparent electrodes in electrical devices without requiring an expensive and toxic process such as dry etching.     

Allyloxy-modified starch with low degree of substitution for fiber reinforced thermoset starch composites

In the present work dough moulding compound premixes of allyl glycidyl ether modified (AGE)-potato starch, (DS) = 0.2, has been prepared and tested for its fiber reinforced composite properties. The AGE-starch was hydrolyzed with α-amylase under neutral condition for 6 h at 45 °C for improved process ability. The grafting and hydrolytic scission was confirmed by nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC), respectively. Homogeneous composite premixes of AGE-starch, wood fibers, various amount of glycerol and ethylene glycol dimethacrylate were successfully mixed with a Brabender-kneader at 55 °C and cured by compression molding at 150 °C using 2 wt% of dibenzoyl peroxide. Adding 5 wt% of glycerol did not reduce the ultimate strength of the composites; 10% glycerol reduced the strength from 60 MPa to 40 MPa, and 16% glycerol to 14 MPa. The results with 5 wt% glycerol are comparable with earlier achieved results. The water absorption rate increased with increased glycerol content and the mechanical strength of the composites was lost completely when the moisture uptake reached 15 wt%.     

Forming behavior and workability of 6061/B4CP composite during hot deformation

Compression tests of 6061/B₄C_P composite have been performed in the compression temperature range from 300 °C to 500 °C and the strain rate range from 0.001 s⁻¹ to 1 s⁻¹. The flow behavior and processing map have been investigated using the corrected data to elimination of effect of friction. The processing maps exhibited two deterministic domains, one was situated at the temperature between 300 °C and 400 °C with strain rate between 0.003 s⁻¹ and 0.18 s⁻¹ and the other was situated at the temperature between 425 °C and 500 °C with strain rate between 0.003 s⁻¹ and 0.18 s⁻¹.The estimated apparent activation energies of these two domains, were 129 kJ/mol and 149 kJ/mol, which suggested that the deformation mechanisms were controlled by cross-slip and lattice self-diffusion respectively. The optimum parameters of hot working for the experimental composite were 350 °C - 0.01 s⁻¹ and 500 °C - 0.01 s⁻¹. In order to exactly predict dangerous damaging mechanism under different deformation conditions exactly, Gegel’s criterion was applied to obtain processing map in the paper. The result showed that the processing map used Gegel’s criterion can be effectively to predict the material behavior of the experimental composite.     

In situ processing and aging behaviour of an aluminium/Al2O3 composite

Reactive sintering involving a displacement reaction between aluminium and CuO powders was applied to fabricate an aluminium based composite. The two powders were mixed in a ball mill and uniaxially pressed before sintering in nitrogen atmosphere at 900 °C. During sintering a displacement reaction between CuO and aluminium occurred, which resulted in in situ synthesis of alumina particles. Differential thermal analysis (DTA), X-ray diffractometry (XRD), optical and scanning electron microscopies were used to investigate the phase and microstructural changes taking place during processing of the composite. Results revealed that no chemical reaction occurred during ball milling and Al₂O₃ phase developed in two stages during sintering of the compact. Below 700 °C, amorphous alumina formed which transformed to crystalline alumina at higher temperature. Aging response of the composite was examined as a function of time in temperature range of 180–220 °C. Composite attained a peak hardness value of 133 H_v after 4 h of aging at 200 °C.     

High temperature fracture behavior of tungsten fiber reinforced copper matrix composites under dynamic compression

W_f/Cu₈₂Al₁₀Fe₄Ni₄ composite was fabricated by flow casting method. Dynamic compression tests with strain rate of 1600 s⁻¹ at 20 °C, 200 °C, 400 °C and 600 °C were finished by means of Split Hopkinson Pressure Bar (SHPB). The results showed that the composites possessed obvious high temperature softening behaviors. The damages of W_f/Cu₈₂Al₁₀Fe₄Ni₄ composites all occurred within the tungsten fibers when compressed at 20 °C, 200 °C and 400 °C, indicating that the interface strength of the composites was high. While the damages of the composites occurred either in the tungsten fibers or in the matrix at 600 °C, in addition, the melt of matrix alloy also occurred. Microstructure of the composites after dynamic compressing at 600 °C was analyzed by transmission electron microscope (TEM), observation revealed that there were a lot of high-density dislocations, stacking faults and twins existing in the matrix. It was also found that the precipitated phase in the matrix played the role of the second phase strengthening.     

Ablation behavior and mechanism of 3D C/ZrC composite in oxyacetylene torch environment

Ablation property of three dimensional carbon fiber reinforced zirconium carbide composite (3D C/ZrC composite) was determined using oxyacetylene torch test with a heat flux of 4187 kW/m² and flame temperature of over 3000 °C. C/ZrC composite exhibited an excellent configurational stability with a surface temperature of over 2000 °C during 60-300 s period, while 3D C/SiC composite was perforated at 55 s. After ablation for 300 s, the composite showed a mass loss rate of 0.006 g/s and a linear recession rate of 0.004 mm/s. The formation of zirconia melt on the surface of the C/ZrC composite contributed mainly the ablation property improvement. The C/ZrC composite after ablation showed four different layers due to the temperature and pressure gradients: the melting layer, the loose tree-coral-like ZrO₂ layer, the undersurface oxidation layer, and the composite layer.     

Simulataneous pentachlorophenol decomposition and granular activated carbon regeneration assisted by dielectric barrier discharge plasma

An integrated granular activated carbon (GAC) adsorption/dielectric barrier discharge (DBD) process was applied to the treatment of high concentration pentachlorophenol (PCP) wastewater. The PCP in water firstly was adsorbed onto GAC, and then the degradation of PCP and regeneration of exhausted GAC were simultaneously carried out by DBD. The degradation mechanisms and products of PCP loaded on GAC were analyzed by EDX, FT-IR and GC–MS. The results suggested that the CCl bonds in PCP adsorbed by GAC were cleaved by DBD plasma, and some dechlorination and dehydroxylation products were identified. The adsorption capacity of adsorption/DBD treated GAC could maintain relatively high level, which confirmed that DBD treatment regenerated the GAC for subsequent reuse. The adsorption of N₂, Boehm titration and XPS were used to investigate detailed surface characterizations of GAC. It could be found that DBD plasma not only increased the BET surface area and pore volume in micropore regions, but also had remarkably impact on the distribution of the oxygen-containing functional groups of GAC.     

Microstructure and mechanical properties of SiCp/AZ91 composite deformed through a combination of forging and extrusion process

In this paper, 10 vol.% SiCp/AZ91 magnesium matrix composites were fabricated by stir casting technology. The as-cast ingots were forged at 420 °C with 50% reduction, and then extruded at 370 °C with the ratio of 16 at a constant ram speed of 15 mm/s. The results showed that the grains were refined during forging. A much finer grain size (∼2.7 μm) of composite matrix was obtained by subjecting the as-forged composite to hot extrusion. The fine SiC particulates restricted the dynamic recrystallized grain growth during the hot extrusion processing, resulting in a remarkable grain refinement. The yield stress and ultimate tensile stress were increased in the as-extruded composite, with the reasons of eliminated casting flaws, the uniform particle distribution and grains refinement. The grain refinement and uniform particle distribution caused an obvious increase in work hardening rate in the as-extruded composite during tensile deformation at room temperature.     

Influence of thermal treatment on the structure and adsorption properties of layered zinc hydroxychloride

Layered zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O) synthesized by hydrolyzing the ZnO particles in aqueous ZnCl₂ solutions at 100 °C for 48 h was outgassed at different temperatures ranging from 100 to 250 °C for 2 h and the structure and adsorption properties of the products were examined by various means. Outgassing at 100-150 °C eliminated the H₂O molecules in interlayer of zinc hydroxychloride. The layered structure of zinc hydroxychloride was disintegrated at 175 °C by breaking the OH?Cl hydrogen-bond in interlayer to form curled thin films composed of poorly crystallized β-Zn(OH)Cl and ZnO, leading to the increment of the specific surface area from 4 to 39 m²/g. The β-Zn(OH)Cl was decomposed at 225 °C to form ZnO. The crystallinity of ZnO was increased on elevating the outgassing temperature, giving rise to the UV absorption property. The H₂O and CO₂ adsorption measurements revealed that the zinc hydroxychloride outgassed at 100-150 °C possessed a high H₂O and CO₂ adsorption selectivity, and the selectivity diminished by the formation of thin films of ZnO above 175 °C.     

Impression creep behaviour of magnesium alloy-based hybrid composites in the transverse direction

The creep behaviour of a creep-resistant AE42 magnesium alloy reinforced with Saffil short fibres and SiC particulates in various combinations has been investigated in the transverse direction, i.e., the plane containing random fibre orientation was perpendicular to the loading direction, in the temperature range of 175–300 °C at the stress levels ranging from 60 to 140 MPa using impression creep test technique. Normal creep behaviour, i.e., strain rate decreasing with strain and then reaching a steady state, is observed at 175 °C at all the stresses employed, and up to 80 MPa stress at 240 °C. A reverse creep behaviour, i.e., strain rate increasing with strain, then reaching a steady state and then decreasing, is observed above 80 MPa stress at 240 °C and at all the stress levels at 300 °C. This pattern remains the same for all the composites employed. The reverse creep behaviour is found to be associated with fibre breakage. The apparent stress exponent is found to be very high for all the composites. However, after taking the threshold stress into account, the true stress exponent is found to range between 4 and 7, which suggests viscous glide and dislocation climb being the dominant creep mechanisms. The apparent activation energy Q_c was not calculated due to insufficient data at any stress level either for normal or reverse creep behaviour. The creep resistance of the hybrid composites is found to be comparable to that of the composite reinforced with 20% Saffil short fibres alone at all the temperatures and stress levels investigated. The creep rate of the composites in the transverse direction is found to be higher than the creep rate in the longitudinal direction reported in a previous paper.     

The effects of thermal fatigue on a SiC fibre/aluminosilicate glass composite

The thermal fatigue (TF) of ceramic matrix composites introduces stresses within the composite due to the thermal expansion mismatch of fibre and matrix; this will affect the lifetime and dimensional stability of the composite. A review of various laboratory TF methods is given, and the controlled, photon heating method used in this research is explained. A Nicalon fibre/glass matrix composite was subjected to rapid, controlled TF from 250 to 700 °C and 250 to 800 °C under no load and dead load conditions in order to illustrate a variety of elastic and inelastic cyclic strain conditions. To characterize simple environmental exposure at elevated temperature, ageing experiments were also run. After TF, the surfaces of the composites were characterized using SEM for evidence of thermal damage and microcracking. The composites were then tested for flexural strength. Results show that the tensile modulus after TF testing remains constant, and that dimensional changes are slight, except near any local hot spots. The 700 °C maximum TF specimens showed appreciably greater embrittlement and lower strength than the 800 °C maximum TF specimens. Observations in the SEM of the surfaces of the 700 °C specimens showed little matrix flow of the type which could decrease oxygen infiltration. Greater matrix flow was observed for the 800 °C specimens. Thermally aged specimens gave results similar to those for the TF experiments.     

Enchanced high-temperature performances of SiC/SiC composites by high densification and crystalline structure

We report the enchanced in situ performances of tensile strength and thermal conductivity at elevated temperatures of the PCS-free SiC/SiC composite with a high fiber volume fraction above 50% fabricated by NITE process for nuclear applications. The composite was fabricated by the optimized combination of the fiber coating, the matrix slurry and the pressure-sintering conditions, based on our previous composites’ study history. The composite showed the excellent tensile strength up to 1500 °C, that it retained approximately 88% of the room-temperature strength. Also, the thermal conductivity of the composites represented over 20 W/m K up to 1500 °C, which was enough high to take the advantage of the assumed design value for nuclear applications. Microstructural observation indicated that the excellent high-temperature performances regarding tensile strength and thermal conductivity up to 1500 °C were the contribution to the high densification and crystalline structure in matrix.     

Dynamic compressive behavior of unidirectional IM7/5250-4 laminate after thermal oxidation

Fiber reinforced high temperature polymer matrix composites are currently gaining wide usage in aircraft structures, especially in airframe and engine inlet casing. The failure of composites in worst-case operational conditions mandates the extensive investigation of the mechanical behavior, and the durability in long-term performance and service life under thermal oxidation. In this work, unidirectional IM7 carbon fiber reinforced high-temperature BMI resin composite (IM7/5250-4) were isothermally aged in air for 2 months at 195 °C and 245 °C, respectively. The dynamic behavior of thermally aged composites was investigated on a split Hopkinson pressure bar (SHPB) in three principal directions. The results indicate that thermal oxidation leads to significant reduction in both stiffness and strength of the composites. Optical micrographs of fracture surface and failure pattern of composite after SHPB impact reveals oxidation induced debonding along the fiber–matrix interface due to oxygen diffusion under long-term exposure to elevated temperatures.     

Effect of multidirectional forging on microstructures and tensile properties of a particulate reinforced magnesium matrix composite

A particulate reinforced magnesium matrix composite prepared with stir casting was subjected to multidirectional forging (MDF). The results showed that after 1 MDF pass the grain size of matrix in the composites decreased compared with as-cast composite, and increased with increasing the MDF temperature from 370 °C to 450 °C. With increasing the MDF passes at 370 °C, the particle distribution of the composite was improved until 3 MDF passes while the grain size of matrix in the composite reached a minimum after 4 MDF passes. Both the yield strength and the ultimate tensile strength of the composite were enhanced with increasing the MDF passes.