Microstructure and oxidation behaviour of SiC fibre-reinforced Si3N4-AlN-Al2O3-Y2O3 matrix composites

A series of SiC fibre-reinforced Si₃N₄-AlN-Al₂O₃-Y₂O₃ matrix composites with different matrix compositions are fabricated by slurry infiltration followed by hot pressing at 1600°C for 30 min. The diffusion of yttrium and aluminium into fibres is apparent during the high temperature processing. All the as-processed composites show fracture with fibre pull-out. After heat treatment in air at 1000°C for 60 min, composites with minimal Y₂O₃ and Al₂O₃ in the matrix composition demonstrate the fracture behaviour with most extensive fibre pull-out. Composites with the highest aluminium and yttrium oxide content form an yttrium–aluminium–garnet phase and an aluminosilicate glassy phase. The latter phase provides an oxygen diffusion path, resulting in the removal of the carbon-rich interphase by oxidation. This results in catastrophic fracture without fibre pull-out after heat treatment of the composite in air.     

Factors affecting the microstructure and mechanical properties of Ti-Al3Ti core-shell-structured particle-reinforced Al matrix composites

This work studied the effects of matrix powder and sintering temperature on the microstructure and mechanical properties of in situ formed Ti–Al₃Ti core–shell-structured particle-reinforced pure Al-based composites. It has been shown that both factors have significant effects on the morphology of the reinforcements and densification behaviour of the composites. Due to the strong interfacial bonding and the limitation of the crack propagation in the intermetallic shell during deformation by soft Al matrix and Ti core, the composite fabricated using fine spherical-shaped Al powder and sintered at 570 °C for 5 h has the optimal combination of the overall mechanical properties. The study provides a direction for the optimum combination of high strength and ductility of the composites by adjusting the fabrication parameters.     

Dissolution of Al2O3-polystyrene latex composites: a fluorescence study

This work reports the use of the steady state fluorescence (SSF) technique to study dissolution of a composite film formed from a mixture of Al₂O₃ and polystyrene (PS) latex particles. The composite films were cast from dispersion of pyrene (P)-labeled PS particles in Al₂O₃ solution at room temperature and annealed at 280°C temperature for 10 min. Eight different composite films were studied in various latex contents. Toluene was used as dissolution agent. Fluorescence intensities I _P from P were monitored during dissolution. Fickian diffusion was employed to model the dissolution processes. Dissolution coefficients, D _d, were measured and found to be increased at high PS content in the composite films.     

Effects of Interface Structures on the Application Properties of Ni/Al Clad Composite

The Ni/Al clad metal composite can be applied for the ultrasonic welding of nickel and aluminum structures for lithium-ion cell packaging. The roll bonding Ni/Al clad sheets with 0.15 mm thickness were produced and the effects of interface microstructures and phase transformation on the application properties of such composites are studied in this investigation. The results show that the interface of Ni and Al forms a jagged, interlocking pattern at the rolling state but not a metallurgical bonding. During the annealing process, the first formed Al₃Ni phase in the interface of Ni and Al is beneficial to their bonding together but the sequently formed Al₃Ni₂ phase results in the formation of cracks and the separation of the Ni/Al layers. The bonding mechanism changes to metallurgical bonding with the formation of such phases. The Ni/Al clad sheet acquires good bending endurance, stable welding strength and suitable electrical resistivity with annealing from 425 to 475°C for 1 h.     

Interface characteristics and mechanical properties of short carbon fibers/Al composites with different coatings

Three kinds of coatings, Ni, Cu and Al₂O₃, were obtained on the surface of short carbon fibers (SCFs). The interface characteristics and mechanical properties of SCFs/Al composites with the various coatings were systematically studied in this paper. The results showed that, compared to non-coating, Ni or Cu coating improved the wettability of SCFs and Al melt. However, the harmful phases Al₃Ni or CuAl₂ generated in interface zone and Al matrix result in the lower mechanical properties. Al₂O₃ coating protected the SCFs and prevented the harmful reaction of Al and SCFs. The interface of Al/Al₂O₃/SCF without any other phase was clean and well bonded, and the Al₂O₃-coated SCFs/Al composite had the highest mechanical properties. The interfacial indentation and fracture mechanism of all the composites were analyzed in detail.     

Effect of heat treatment on the mechanical and microstructural characterization of Mg-AZ91E/TiC composites

Mg-AZ91E/TiC_p composite was fabricated using a spontaneous infiltration technique at 950 °C under an argon atmosphere. The composites produced have 37 vol.% of metal matrix and 63 vol.% of TiC-like reinforcement. The obtained composites were subsequently solution heat-treated at 413 °C during 24 h, cold water quenched, and subsequently artificially aged at 168 and 216 °C during 16 h in an argon atmosphere. Effect of heat treatment on the microstructure and mechanical properties was evaluated. Microstructural characterization was analyzed using different techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM). Interface between matrix and reinforcement was examined using transmission electron microscopy (TEM), and mechanical properties were evaluated by measuring the elastic modulus and hardness. Mg, TiC, Al, and Mg₁₇Al₁₂ phases through XRD were detected. Meanwhile, using TEM analysis in heat-treated composites MgAl₂O₄, MgO, and Al₂O₃ were identified. The as-fabricated composite have elastic modulus and hardness of 162 GPa and 316 Hv, respectively. After solution heat treatment and aging at 168 °C during 12 h, the composites reaches values of 178 GPa and 362 Hv for the elastic modulus and hardness, respectively. Time of aging was correlated with measures of elastic modulus and hardness.     

Electron microscopic study on interfacial characterization of electroless Ni-W-P plating on aluminium alloy

The interface between electroless plating Ni-W-P deposit and aluminium alloy (Al) matrix at different temperature heated for 1 h was studied using transmission electron microscope. The results show that the interface between as-deposited Ni-W-P deposit and Al matrix is clear. There are no crack and cavity. The bonding of Ni-W-P deposit and Al matrix is in good condition. The Ni-W-P plating is nanocrystalline phase (5-6 nm) in diameter. After being heated at 200 °C for 1 h, the interface of Ni-W-P deposit and Al matrix is clear, without the appearance of the diffusion layer. There exist a diffusion layer and educts of intermetallic compounds of nickle and aluminium such as Al₃Ni, Al₃Ni₂, NiAl, Ni₅Al₃ and so on between Ni-W-P deposit and Al matrix after being heated at 400 °C for 1 h.     

Influence of heat treatment on microstructure and mechanical properties of the interface in an EN AW-6082/1.4310 composite extrusion

The presented paper deals with a unidirectional steel wire reinforced aluminum matrix composite manufactured by composite extrusion. The main objective of this work was to determine the effect of heat treatment, and the influence of long solution annealing times on the composites interface regarding microstructural changes and the resulting interface strength. For evaluation of the microstructure high resolution transmission electron microscope (TEM) investigations accompanied with electron dispersive X-ray spectroscopy (EDX) were performed. It could be shown that diffusion from the steel wire into the aluminum matrix occurs and that the diffusion paths as well as particle formation is influenced by the preceded heat treatment. Diffusion paths in the range of 40–150 nm could be observed for Al, Fe, Cr and Ni. After annealing times over 5 h an extensive growth of an intermetallic reaction layer was found. The mechanical properties of the interface were determined by push-out-tests and tensile tests radial to the interface, which provided the debonding shear strength σ_deb and for the latter experiment the interfacial radial strength σ_IR. It has become apparent that debonding shear strength is highly influenced by matrix properties. In radial tensile tests the failure is predominantly controlled by the chemical bond of the interface. It was shown that interface strength of specimen with small reaction zones of about 3 μm were beneficial for the mechanical behavior in both loading conditions. Longer annealing times showed a drastic decrease of interface shear strength. It was concluded from EDX measurements and in comparison with literature that the reaction zone is dominated by the growth of Al₅Fe₂ (η-phase).     

Studies on interfacial adhesion in unidirectional isora fibre reinforced polyester composites

Unidirectional isora fibre reinforced polyester composites were prepared by compression moulding. Isora is a natural bast fibre separated from the Helicteres isora plant by a retting process. The effect of alkali treatment on the thermal properties of the fibre was studied using TGA, DTA and DSC in oxygen and nitrogen atmosphere. Mechanical properties like tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali-treated fibres have been studied as a function of fibre loading. The optimum loading for tensile properties of the composite containing untreated fibre was found to be 45% by volume and on alkalization of the fibre, the optimum loading increased to 66%. For flexural properties the loading was optimized at about 56% and 66%, for the composites containing untreated and alkali treated fibres, respectively. From DMA studies it was observed that the alkali-treated fibre composites have higher E′ and E″ values compared to untreated fibre composites. From swelling studies in styrene it was observed that the mole percent uptake of the solvent by the treated fibre composites is less than by the untreated fibre composites. From these results it can be concluded that in composites containing alkalized fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Reaction mechanisms between Al and Fe3O4 powders in the formation of an Al-based metal matrix composite

The reaction mechanisms between Al and Fe₃O₄ powders were investigated. Differential thermal analysis revealed that a two-step displacement reaction between Al and Fe₃O₄ took place during sintering. Initially, the Fe₃O₄ was converted to amorphous FeO at ～720°C and some of the Al was oxidized to amorphous Al₂O₃. In the final stage, when the temperature reached ～840°C, crystalline Al₂O₃ particles were produced in the molten Al–Fe liquid. The effects of cooling rate on the microstructures were studied. When the Al–Fe liquid was furnace-cooled to room temperature, proeutectic Al₃Fe plates, plate-like divorced eutectic Al₃Fe and Al₂O₃ particles were in situ formed in the Al(Fe) matrix. While quenching from 700°C, nanometer-sized Al dendrites and Al–Al₆Fe eutectic lamellae were produced in the Al matrix. However, when it was rapidly quenched from 900°C, the size of the proeutectic Al₃Fe phases was further reduced and Al₆Fe nanorods were found in the Al–Al₆Fe eutectics. A model was proposed to describe the transformation of the Al–Fe intermetallics during solidification.     

Comparison of fibre/matrix interface strength for a 3D woven SiC/SiC composite

The fibre/matrix interface shear strength, τ _P, was determined by analysis of fibre pullout length distributions for a 3D woven SiC/SiC-based composite that had undergone tensile testing between room temperature and 1300°C in vacuum and air. Data was compared with the fibre/matrix interface shear strength, τ _S, obtained previously for this system by analysis of in situ fibre strength distributions. τ _P was found to follow the same general trend as that of τ _S and this was explained in terms of the carbon-rich fibre/matrix interface region. However, τ _P was smaller than τ _S by a factor of 3-4 for all cases, but the reason for this remains unclear although several tentative suggestions have been put forward.     

The diffusion of silicon atoms in stack structures of La2O3 and Al2O3

The interfacial reactions and electrical characteristics of stack structures of La₂O₃ and Al₂O₃ were investigated as a function of the annealing temperature. In the case of Al₂O₃/La₂O₃/Si (ALO structure), the La₂O₃ in contact with the Si substrate was readily transformed into La-silicate by the diffusion of Si atoms, while in the case of La₂O₃/Al₂O₃/Si (LAO structure), interfacial reactions between the Al₂O₃ layer and the Si substrate were suppressed. After an annealing treatment at 700 °C, the Al₂O₃ in the ALO structure can play an effective role in blocking the hydration of La₂O₃, resulting in an unchanged interfacial layer. However, the Al₂O₃ layer in the LAO structure was unable to suppress the diffusion of Si atoms into the La₂O₃ film. When the annealing temperature reached 900 °C, both structures showed a similar depth distribution with a high content of Si atoms diffused into the films. The change in the elemental distributions via the diffusion and reaction of Si atoms affected the electrical characteristics at the interface between ALO/LAO structure and Si substrate, specifically the trap charge density (D_it) and band gap (E_g) values.     

Interfacial microstructure and growth mechanism of Al4C3 in Grf/Al composites fabricated by liquid pressure method

In this study, Gr_f/Al composite was fabricated by liquid pressure method. The diffusion layer and the nucleation and growth of Al₄C₃ were observed at the interface of Gr_f/Al composites by TEM and HRTEM. The growth mechanism of Al₄C₃ was analyzed in detail by crystallography theory. It was found that Al₄C₃ had no phase relations with the carbon fiber. (0 0 0 1) layer of Al₄C₃ was parallel with main growth direction. Both the diffusion layer at the interface and crystal structure of Al₄C₃ affected the shape of Al₄C₃. At a certain position, Al₄C₃ could connect two fibers when the fibers were close to each other.     

Formation and properties of Al composites reinforced by quasicrystalline AlCuFeB particles

Al-based composites reinforced by icosahedral (i-) Al₅₉Cu_25.5Fe_12.5B₃ quasicrystalline particles were prepared by solid-state sintering. It was found that Al diffusion from the matrix to the quasicrystalline particles induces phase transformation into the ω-Al₇Cu₂Fe tetragonal phase. In order to preserve the i phase, we used an oxidation pre-treatment of the particles and studied its influence on the kinetics of the phase transformation (Al + i → ω) as a function of temperature by high energy X-ray diffraction. The oxide layer acts as a barrier, reducing efficiently the diffusion of Al up to a sintering temperature of 823 K, allowing the control of the phases in the composites. The mechanical properties and the friction behaviour of the composites were investigated and show the negative influence of the oxide on the interface strength.     

The temperature dependence of internal friction in SicPCS/Al composites

In this study the relationship between Q^-1 and the microstructural characteristics of SiC_PCS/Al composites was investigated. Seven specimens made by various processes were divided into three groups and their Q^-1-T spectra were compared. The temperature dependence of internal friction up to 500°C was measured by vacuum inverse torsional pendulum apparatus. For the SiC_PCS/Al composite fabricated by the liquid infiltration method, Q^-1 increased more and more rapidly with rising temperature when the extent of fiber-matrix interfacial reaction intensified. For hot-pressed plates fabricated from preform wires and Al(1050) foils, poor diffusion bonding between the preform wires and A1 foils was introduced; this new interface is primarily responsible for the temperature dependence of Q^-1.     

Optical diagnostics of physicochemical properties of NiO/Al2O3 nanocomposites upon exposure to different gases and heat

We have studied nanostructural and optical properties of composites of nanostructured nickel oxide films on a substrate from porous aluminum oxide NiO/Al₂O₃ in the UV, visible, and IR spectral ranges on exposure of composites to different gases, vacuum, and heat. We have found that, upon irradiation of NiO/Al₂O₃ composites by laser radiation at a wavelength of 633 nm, they demonstrate a high sensitivity to carbon monoxide CO in the range of the excitonic absorption of nickel oxide. We assume that an increase in the transmission coefficient of the composite in the excitonic absorption band is determined by luminescence that is caused by the oxidation reaction of carbon monoxide. The sensitivity of composites to CO is enhanced with decreasing the size of NiO nanoparticles and after evacuation. The values of the diffuse reflection coefficient at the laser radiation wavelength of 633 nm correlate with the size of nickel oxide nanoparticles. Spectral changes in the range of the fundamental absorption band of NiO that occur in the IR range and in diffuse reflection spectra are related to the appearance of carbon-containing compounds in the composite exposed to CO.     

Design of Some Oxide/Metal Composite Supports and Catalysts

Textural, mechanical and catalytic properties of porous composite materials Al₂O₃/Al, MeO _x (Me)/Al₂O₃/Al with metal particles homogeneously distributed in the alumina matrix were studied. These materials were prepared by mixing the powdered components with aluminum followed by hydrothermal treatment and calcination. The macroporous structure was shown to be controlled by the size of large (>microns) particles in starting blends. The mesoporous structure is primarily determined by the properties of alumina formed by dehydration of hydroxide produced in turn via aluminum oxidation by water. The mechanical strength of porous cermets is determined by the number and properties of contacts between micron-size components of composites. Improved catalytic performance of composites is ensured by the developed macroporous structure providing enhanced mass transfer inside the cermet granules.     

Scanning tunneling microscopy study of growth of Pt nanoclusters on thin film Al2O3/NiAl(1 0 0)

The growth of Pt nanoclusters on thin film Al₂O₃ grown on NiAl(1 0 0) was studied by using scanning tunneling microscopy (STM). The samples were prepared by vapor depositing various amounts of Pt onto the Al₂O₃/NiAl(1 0 0) at different substrate temperatures in ultra high vacuum (UHV). The STM images show that sizeable Pt nanoclusters grow solely on crystalline Al₂O₃ surface. These Pt clusters appear to be randomly distributed and only a few form evident alignment patterns, contrasting with Co clusters that are highly aligned on the crystalline Al₂O₃. The size distributions of these Pt clusters are rather broader than those of the Co clusters on the same surface and the sizes are evidently smaller. With increasing coverage or deposition temperature, the number of larger clusters is enhanced, while the size of the majority number of the clusters remains around the same (0.4 nm as height and 2.25 nm as diameter), which differs drastically from the Pt clusters on γ-Al₂O₃/NiAl(1 1 0) observed earlier. These Pt cluster growth features are mostly attributed to smaller diffusion length and ease to form stable nucleus, arising from strong Pt-Pt and Pt-oxide interactions and the peculiar protrusion structures on the ordered Al₂O₃/NiAl(1 0 0). The thermal stability of Pt nanoclusters was also examined. The cluster density decreased monotonically with annealing temperature up to 1000 K at the expense of smaller clusters but coalescence is not observed.     

Phase Characterization of Diffusion Soldered Ni/Al/Ni Interconnections

The formation and growth of intermetallic phases in the Ni-Al system during a novel joining process for Ni/Ni interconnections based on diffusion soldering has been studied. The Ni/Al/Ni bonds were accomplished by isothermal solidification and subsequent interdiffusion of Ni and Al in the Ni/Al/Ni joints held at a temperature of 720°C. Optical and scanning electron microscopy, electron probe microanalysis and X-ray diffraction analysis were used to characterize the microstructural changes as a function of the reaction time. The following phases appeared sequentially: liquid Al → Al₃Ni → Al₃Ni₂ → AlNi (stoichiometric) → AlNi (Ni-rich) → AlNi₃. At intermediate stages two to four phases coexisted. The NiAl phase occurred in two variants, namely a Ni-rich AlNi (60 at.% Ni) and stoichiometric AlNi. The joining process was completed after 30 h of reaction. Then only AlNi₃ was present in the Ni/Al/Ni interconnection zone. The quality of the resultant bond and the high melting point of the AlNi₃ phase (1360°C) indicate a great potential of the diffusion soldering for the joining of heat dissipating devices used in electronics and electrotechnics.     

Effect of curing temperature,fibre loading and bonding agent on the equilibrium swelling of isora-natural rubber composites

Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and 150°C using a low temperature curing accelerator system. Composites were also prepared using a conventional accelerator system and cured at 150°C. The swelling behavior of these composites at varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent uptake decreased, due to the superior solvent resistance of the fibre and good fibre–rubber interactions. The bonding agent improved the swelling resistance of the composites due to the strong interfacial adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (V_τ ) was found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre composite showed a lower percentage swelling than untreated one for both systems showing superior rubber–fibre interactions.