Heat Treatment Of Particles Research Articles

PROPERTIES OF ALUMINIUM/ELECTROLESS Ni-COATED SiC COMPOSITES - A REVIEW

The combination of properties of Al/SiC composites make them very attractive materials for applications in automotive and aerospace industries. Several techniques are used in developing Al/SiC composites but stir casting process is most commonly used because it is the simplest and cost effective technique. However, composites produced via stir casting suffer from limitations such as low wettability and inadequate bonding between the molten Al & SiC particulates and the formation of degrading interfacial products like aluminum carbide (Al4C3) which degrades the mechanical properties of the composite. Some of the techniques to improve Al-SiC wettability include addition of surface active elements such as magnesium, heat treatment of particles and application of metallic coating on the reinforcements before addition to the melt. Wetting agents alter the composition of the matrix alloy, while heat treatment of the reinforcement does not completely prevent the formation of Al4C3 when utilized. To reduce the direct interaction and promote wetting between reinforcements and molten aluminum during processing, the surface of SiC particulates can be modified by coating via oxidation, sol-gel and electroless processes. Of all these methods, electroless nickel deposition produces the best coatings with uniform thickness and adequate strength. In the present study, influence of electroless nickel-coating of SiC on the mechanical, corrosion and microstructural properties of Al/SiC composite has been evaluated. Finally, it can be concluded that the Ni and Ni3P intermetallic phases produced via electroless coating improves the wettability between the SiC and molten aluminium leading to enhanced properties of the composite.

Ultra-high stability and durability of iron oxide micro- and nano-structures with discovery of new three-dimensional structural formation of grain and boundary

In this research, we have applied a facile polyol method with the addition of NaBH4 to synthesize polyhedral α-Fe2O3 oxide microparticles with the large size of 1–10μm at 200–230°C for about 25–30min. The sharp polyhedral shapes and morphologies have been formed in the good assistance of NaBH4 as versatile strong reducing agent. The sharp polyhedral and large Fe oxide microparticles exhibited a uniform characterization of size, shape and morphology with the pure α-Fe2O3 structure. To study durability and stability of the microparticles under temperature, we have rationally carried out isothermal heat treatment of the prepared α-Fe2O3 oxide microparticles at high annealing temperature about 500°C and 900–910°C for 1h. A new structure was found in the pure α-Fe2O3 particles with micro- and nano-structure co-existed with the very good formation of a three-dimensional (3D) structure with the oxide grains and the boundaries. The interesting phenomena of the deformation of surface, size, shape, and structure are discovered in α-Fe2O3 oxide microparticles by isothermal heat treatment. Apart from surface deformation, the new micro- and nano-structure of large α-Fe2O3 microparticles cannot be destroyed but they can be retained in their specific characteristics of size, shape, and morphology because of both plastic and elastic deformation co-existed. The interesting surface deformation by heat treatment is observed in comparison with the case without heat treatment. The typical magnetic properties of α-Fe2O3 microparticles were investigated in the appearance of grain and boundary. Finally, our proposal of the new technologies with particle heat treatment is very crucial to make novel micro- and nano-structures of ultra-high durability and stability with the grains and the boundaries that can be utilized in catalysis, energy and environment for future.

Microstructure and mechanical properties of Al–Al2O3 micro and nano composites fabricated by stir casting

Abstract Aluminum matrix composites (AMCs) reinforced with micro and nano-sized Al2O3 particles are widely used for high performance applications such as automotive, military, aerospace and electricity industries because of their improved physical and mechanical properties. In this study, in order to improve the wettability and distribution of reinforcement particles within the matrix, a novel three step mixing method was used. The process included heat treatment of micro and nano Al2O3 particles, injection of heat-treated particles within the molten A356 aluminum alloy by inert argon gas and stirring the melt at different speeds. The influence of various processing parameters such as heat treatment of particles, injection process, stirring speed, reinforcement particle size and weight percentage of reinforcement particles on the microstructure and mechanical properties of composites was investigated. The matrix grain size, morphology and distribution of Al2O3 nanoparticles were recognized by scanning electron microscopy (SEM), optical microscope (OM) equipped with image analyzer, energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Also, the hardness and compression strength of samples was investigated. The results showed the poor incorporation of nano particles in the aluminum melt prepared by the common condition. However, the use of heat-treated particles, injection of particles and the stirring system improved the wettability and distribution of the nano particles within the aluminum melt. In addition, it was revealed that the amount of hardness, compressive strength and porosity increased as weight percentage of nano Al2O3 particles increased.