Homogeneous Distribution Of Reinforcement Research Articles

Electroless nickel coated short carbon fibres in aluminium matrix composites

Abstract Electroless nickel coated fibres have been used as reinforcement for the fabrication of aluminium matrix composites by liquid processing. Uniform, continuous and well-adhered nickel coatings are obtained with different phosphorus contents. Coated carbon fibres were mixed with AA6061 aluminium powders, compacted and heated at temperatures from 650 to 950 °C to study the reactivity, the nickel diffusion, and the resulting interfaces. Coatings improve the wetting behaviour of carbon fibres by molten aluminium because of the formation of a transient Al–Ni intermetallic at the matrix–fibre interface, limiting fibre segregation to obtain a homogeneous reinforcement distribution. Finally, the mechanical properties of the composite have been measured through nanoindentation tests.

Monitoring of Carbon Fiber/Polyamide Composites Processing by Rheological and Thermal Analyses

The use of continuous carbon fiber reinforced thermoplastic composites in the aerospace and automotive fields has increased due to their high performance. The hot compression molding process for the manufacture of the composites has attracted much interest due mainly to the high rate of production and quality of the finished parts. This work involves the use of rheological and thermal analyses for the optimization of the processing parameters related to the manufacture of carbon fabric/polyamide 6 and 6/6 by hot compression molding. The results show that the most adequate processing temperatures to be used in the hot compression molding are 250°C and 290°C for polyamides 6 and 6/6, respectively. The loss moduli value (G″) from DMA increased with the increment of the carbon fiber content in the glass transition temperatures, due to the reinforcement contribution. Therefore, the glass transition temperatures of all samples remained constant. The use of the established parameters based on the DSC, DMA, and rheological analyses favored the manufacture of composites with a homogeneous distribution of reinforcement and matrix as observed through optical microscopy analyses.

The effect of a dilution agent on the dipping exothermic reaction process for fabricating a high-volume TiC-reinforced aluminum composite

A synthesis of in situ formed TiC/Al composites utilizing the reaction between molten aluminum and preforms consisting of Ti, C, Al and TiC powder was studied. The addition of TiC powder as a dilution agent controlled the explosive exothermic reaction and played a key role in the homogeneous distribution of reinforcement.

Reheating Process of Metal Matrix Composites for Thixoforming and Their Inductive Coil Design

In this work, the fabrication processes of particulate metal matrix composites (PMMCs) with a homogeneous distribution of reinforcement and their reheating for thixoforming were studied. Electromagnetic stirring was used to fabricate PMMCs to vary particle size. PMMCs were tested before and after the reheating process using a tensile test with and without heat treatment. The combined process conditions for fabricating the PMMCs are also suggested for a variety of particle sizes. For the thixoforming of PMMCs, fabricated billets are reheated by using an induction heating system with a maximum capacity of 20 kW. The effects of the dispersion state of the reinforcements on the reheating temperature and microstructural morphology were investigated.

Fatigue behaviour of Ti sputtered Al composites

Remarkable enhancement of fatigue life and endurance limit of Al matrix composites has been achieved by thin coatings of Ti sputtered at room temperature. Three materials have been investigated. They differ for matrix (6061, A359, 2618), reinforcement particles (SiC and Al2O3) and preparation process (casting and powder metallurgy). Fatigue tests employing a rotating bending machine showed that the method works on all of them, higher effectiveness has been observed in the composite (6061/ 20%SiCp) which has more homogeneous reinforcement distribution. An improvement of fatigue behaviour has been observed also in tests performed on the composite A359/20%SiCp at 200°C, typical working temperature for some industrial applications of Al matrix composites. Coatings seal the defects present on the external surface of the composites, retard crack growth thus lead to an improvement of fatigue behaviour. The effect of coating on fatigue behaviour is discussed with reference to the surface state, which has been investigated by scanning electron microscopy (SEM), scanning tunnelling microscopy (STM), X-ray diffraction (XRD) and microhardness tests.

Bi-continuous metal matrix composites

Bi-continuous alumina/aluminium composites were made by infiltrating an alumina preform which had the structure of a reticulated ceramic foam. The low density preforms were prepared from a polyurethane suspension of alumina powder which was pyrolysed and sintered after foaming. Higher density preforms consisted of ceramic foams with open cells. All these preforms were infiltrated with 6061 aluminium alloy using a modified squeeze caster fitted with a vacuum system and fine control of speed and pressure. The microstructure of the preform fitted an established relationship between the ratio of window diameter to cell diameter ( k) and void volume fraction ( V p). Low k foams were infiltrated fully but on cooling below the solidus, interfacial debonding took place due to differential thermal contraction. This was overcome by modifying the processing conditions. High k foams which had high fractional porosity, retained sound interfacial bonding. The composites possess higher elastic modulus than conventional MMCs with a homogeneous reinforcement distribution at a given volume fraction. The loss of electrical conductivity is negligible in the lower volume fraction range because of the three dimensionally continuous aluminium phase. The experimental results are compared with a number of theoretical predictions.

Mechanical solid state mixing for synthesizing of SiC p/Al nanocomposites

High-energy ball milling was successfully employed to fabricate the metal matrix composite (MMC) of Al reinforced with SiC particulate (SiC p) with distinct nanocrystalline characteristics. The powders of the end-products (86 ks of milling time) of the mechanically-mixed nanocomposites SiC x Al 100− x ( x=2, 5, 7, 10 vol. %) that have spherical-like morphology (less than 0.5 μm in diameter) were consolidated into bulk compacts, using a plasma activated sintering method. Density measurements show that this consolidation step leads to the formation of fully dense bulk samples. Moreover, the consolidated SiC x Al 100− x samples reveal a nanocrystalline structure with a homogeneous reinforcement distribution of SiC p in the Al matrix. Reactive products, i.e. Al 4C 3 and Si, could not be detected on the interfaces between the reinforcement and the matrix in both mechanically mixed powders and consolidated samples. The mechanically mixed powders and consolidated compacts have been characterized by means of X-ray diffraction, scanning and transmission electron microscopes, optical metallography and chemical analyses. The hardness and some mechanical properties of SiC p/Al have been determined as a function of SiC p content.

Microstructure and properties of spray-deposited 2014+15 vol pct SiC particulate-reinforced metal matrix composite

A metal matrix composite (MMC) of 2014 aluminum alloy reinforced with 15 vol pct SiC particulate was produced by the spray-forming-deposition process. The as-deposited preform revealed a high density and a homogeneous reinforcement distribution. Reactive products were not found on interfaces between the reinforcement and the matrix. Compared to the control alloy, the composite showed accelerated aging after solutionizing at 502 °C, while aging was retarded after solutionizing at 475 °C. Analysis indicated that the activation energy was almost the same for the aging process after different solutionizing treatments. This suggested that while the thermal barrier for the aging process was the same, other factors affecting the aging process should be considered. For example, the effective concentration of the precipitate forming elements possibly decreased after incompletely solutionizing at 475 °C. After heat treatment, the composite showed a tensile strength similar to the control alloy. The wear resistance of the composite improved considerably. The aging behavior of the composite was also studied using the nanoindentation technique. Steep gradient distribution of elastic modulus and hardness around the reinforcement SiC particulate was observed. Theoretical analysis showed that this could be attributed to the gradient distribution of precipitates, resulting from a gradient distribution of dislocation density around the SiC particulates caused by residual thermal misfit stresses.