AlC Composites Research Articles

Synergetic Effect of Discontinuous Carbon Fibers and Graphite Flakes on Thermo-Mechanical Properties of Aluminum Matrix Composites Fabricated by Solid–Liquid Phase Sintering

Aluminum (Al) matrix composite materials reinforced with graphite flakes (GF) and pitch-based carbon fibers (CF) were fabricated by solid–liquid phase sintering with a small amount of Aluminum–Silicon eutectic alloy (Al-12 wt%Si). The amount of Al–Si is optimized for a carbon content of 50 vol% in order to achieve, in the plane of GF reinforcement, a higher thermal conductivity (TC) and a lower coefficient of thermal expansion (CTE) compared to identical composite material fabricated by conventional powder metallurgy route. Al/(GF + CF) composite materials were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray microscopy and X-ray tomography in order to highlight the distribution of the Al–Si liquid phase and the formation of a carbon network in the aluminum matrix. A small amount of CF allows to control the through-plane CTE without affecting significantly the in-plane TC of the Al-C composites. The (GF + CF) mixture and the solid–liquid phase sintering allow to achieve a TC of 410 W/m K (in-plane direction) and a CTE of 2.4 × 10−6/K (trough-plane direction), which is, for example, applicable for lightweight heat sink material.

Fabrication and mechanical properties of pressureless melt infiltrated magnesium alloy composites reinforced with TiC and Ti 2 AlC particles

Abstract Herein we report on the fabrication and mechanical properties of Mg composites fabricated by pressureless melt infiltration of Mg and Mg alloys into porous preforms of TiC and Ti 2 AlC. The latter is a member of the MAX phases – viz. layered, machinable, ternary carbides and nitrides – some of which are relatively light and stiff. In this study, pure Mg and three, commercially available, aluminum-containing Mg alloys – AZ31, AZ61 and AZ91 – were used as matrices at a loading of ≈50 vol%. For the most part, increasing the Al content enhanced the elastic moduli, Vickers hardness values and yield and ultimate compressive strengths. Reducing the particle sizes of the TiC and Ti 2 AlC particulate reinforcements also had a large impact on the mechanical properties. At 1028±5 MPa, the ultimate compressive strength of a TiC–AZ61 composite, in which the TiC particle size distribution is Lorentzian and centered at, d c =0.41±0.01 µm, was ≈40% higher than that of the same composite with coarser TiC particles with a bimodal size distribution centered around d c =1.6±0.1 µm, and 5.8±0.3 µm. In addition, the elastic modulus and Vickers hardness of the former composite were measured to be 174±5 GPa and 3.4±0.3 GPa, respectively. For the Ti 2 AlC reinforced composites, the best properties were obtained when AZ61 was reinforced with Ti 2 AlC particles with d c =0.51±0.01 µm. The enhancements in elastic and mechanical properties are attributed to the presence of a strong interface mediated by the presence of Al in the matrix, finer reinforcement particle sizes and finer grained Mg-matrices. The Ti 2 AlC composites are slightly lighter and can be fabricated at lower temperature than comparable TiC composites; the former are also readily machinable but more expensive.

Formation of MAX solid solutions (Ti,V)2AlC and (Cr,V)2AlC with Al2O3 addition by SHS involving aluminothermic reduction

Abstract MAX solid solutions (Ti,V) 2 AlC and (Cr,V) 2 AlC with Al 2 O 3 addition were produced by solid state combustion involving aluminothermic reduction in the mode of self-propagating high-temperature synthesis (SHS). Starting materials included TiO 2 /V 2 O 5 /Al/Al 4 C 3 and Cr 2 O 3 /V 2 O 5 /Al/Al 4 C 3 powder mixtures. Attempts were made to attain (Ti 1− x V x ) 2 AlC and (Cr 1− y V y ) 2 AlC with the V content in terms of x and y from 0.1 to 0.7. Combustion exothermicity was increased by increasing V 2 O 5 for the yield of a higher proportion of V at the substitution site, which not only increased the combustion temperature and reaction front velocity, but also facilitated the evolution of solid solutions. Due to insufficient reaction exothermicity, (Ti 1− x V x ) 2 AlC/Al 2 O 3 in situ composites were only produced under x ≥0.4. On the other hand, the formation of (Cr 1− y V y ) 2 AlC/Al 2 O 3 was achieved with y from 0.1 to 0.7, because reduction of Cr 2 O 3 is more energetic than that of TiO 2 . The laminated microstructure characteristic of the MAX ternary carbide was observed for both Al 2 O 3 -added (Ti,V) 2 AlC and (Cr,V) 2 AlC composites synthesized in this study.

Dispersity of materials obtained by mechanical activation and laser sintering of Al-C systems and used for production of electrochemical capacitors

Characteristics of materials designed for electrodes of electrochemical capacitors based on mechanically activated Al-C composites applied onto aluminum foil by laser sintering are considered. The methods of X-ray diffraction, X-ray photoelectron spectroscopy, and transmission and scanning electron microscopy are used to study the structure and composition of synthesized layers. It is established that mechanical activation of aluminum in the presence of graphite followed by high-speed laser sintering of the obtained material on an aluminum foil substrate noticeably increases material dispersity with a rise in its specific surface area from an initial value of 4 m2/g to a value on the order of 1000 m2/g, as estimated from the data on the capacity of the electrical double layer.

Microstructure and mechanical properties of in situ synthesized Ti2AlC/Al2O3 composites

Abstract Al 2 O 3 particle-reinforced Ti 2 AlC composites are successfully synthesized from the powder mixture of Ti, TiC, Al and TiO 2 by in situ hot-pressing method. The effect of Al 2 O 3 addition on the microstructure and mechanical properties of the Ti 2 AlC/Al 2 O 3 composites is investigated in detail. It is found that the as-sintered products are mainly composed of Ti 2 AlC matrix and Al 2 O 3 reinforcement, and the in situ formed fine Al 2 O 3 particles tend to disperse on the matrix grain boundaries. With increasing the Al 2 O 3 content, the Rockwell hardness, compressive and flexural strength of Ti 2 AlC/Al 2 O 3 composites gradually increase. But the fracture toughness of the composites increases first then decreases with the increase in the Al 2 O 3 and the Ti 2 AlC/12 wt% Al 2 O 3 sample possesses the maximum value of 5.37 MPa m 1/2 , which is improved by 19.3%.

Preparation of TiAl/Ti2AlC composites with Ti/Al/C powders by in-situ hot pressing

TiAl/Ti2 AlC composites were prepared by in-situ hot pressing of Ti/Al/C powders mixtures and sintered at different temperatures were investigated by X-ray diffraction (XRD) of samples. The reaction procedure of Ti-Al-C system could be divided into three stages. Below 900°C, Ti reacts with Al to form TiAl intermetallics; above 900°C, C reacts with remain Ti to form TiC triggered by the exothermal reaction of Ti and Al; TiAl reacts with TiC to produce dense TiAl/Ti2 AlC composites. In the holding stage, ternary Ti2AlC develops to layered polycrystal and composites pyknosis in the meanwhile. The mechanism of synthesis and microstructure was especially discussed.

Mechanical and Erosion Behaviour of Ti47Al-3W/TI2ALC Composites by Reactive Arc-Melting

Ti-50Al alloy and Ti-47Al-3W alloy and its composites have been prepared by reactive arc melting technique using elemental powders. Composites have been reinforced using 3.5, 10 and 18 vol% of Ti2AlC in the matrix of TiAl with and without addition of W and C. By the addition of tungsten and carbon to TiAl alloy, we have produced composites that are reinforced randomly by reacted rod like Ti2AlC particles with fine precipitate of Ti2AlC particles and B2 particles. Compared to Ti-50Al alloys, the Ti-47Al-3W alloy and its composites have superior mechanical properties like bending strength, hardness, fracture toughness and erosion. Ti-47Al-3W/3.5 vol% Ti2AlC has excellent erosion resistance because of the dispersion of fine Ti2AlC and B2 particles in the matrix.

Synthesis of TiAl(Cr)/Ti<SUB>2</SUB>AlC Composites by Reactive Arc-Melting

TiAl(Cr)/Ti 2 AlC composites have been prepared by a reactive arc-melting technique using elemental powders of Ti, Al, Cr and C. Resulting composites have been reinforced using 3.5, 10 and 18 vol% Ti 2 AlC in a matrix of TiAl with and without addition of Cr. The axial ratio of γ-phase has been lowered through the complete solid solution of chromium. The grain size of the matrix has been found to decrease whereas its distribution converges along the content of Ti 2 AlC. The lamella grains in the matrix have been changed both into TiAl and very fine Ti 2 AlC particles by a homogenizing treatment. Compared to TiAl single-phase alloy, studied composite materials have revealed superior mechanical properties, such as bending strength, compressive strength and fracture toughness. This improvement is caused by the formation of Cr solid-solution for hardening, dispersion of the Ti 2 AlC particles and the fine grain of the TiAl matrix.

Microstructure and Mechanical Properties of L1<SUB>2</SUB>-(Al, Cr)<SUB>3</SUB>Ti/Ti<SUB>2</SUB>AlC Composites Prepared by Combustion Synthesis

L1 2 -(Al, Cr) 3 Ti/Ti 2 AlC composites have been prepared by the reactive arc-melting technique using elemental powders of Ti, Al, Cr, and C. Resulting composites have been reinforced using 4.5, 9, and 18 vol%Ti 2 AlC in a matrix of L1 2 trialuminide Ti-61 mol%Al-13 mol%Cr alloy. The Ti 2 AlC particles having a rod-like morphology of 1.5 μm width and 5-20 μm in length were homogeneously dispersed in the matrix. The matrix grain size was reduced through addition of Ti 2 AlC particles. These composite materials have revealed higher mechanical properties (bending strength and fracture toughness) than that of the monolithic alloy. This improvement is attributed to the Ti 2 AlC particles dispersion and to the fine grain of the matrix.

Microstructure and Mechanical Properties of L1<SUB>2</SUB>-(Al, Cr)<SUB>3</SUB>Ti/TiB<SUB>2</SUB>+Ti<SUB>2</SUB>AlC Composites Produced by Reactive Arc-Melting

The Ll 2 -(Al, Cr) 3 Ti/TiB 2 + Ti 2 AlC composites were prepared by reactive arc-melting from the elemental powders of titanium, aluminum, chromium, and B 4 C powder. The resulting composites have reinforcement 3.8, 7.5, and 15 vol% (TiB 2 + Ti 2 AlC) in the matrix of Ll 2 trialuminide Ti-61Al-14Cr alloy. The TiB 2 particles were mass-like with 5-10 μm in diameter, while the Ti 2 AlC particles were rod-like in shape with 1-2 μm in width and 5-15 μm in length and they are homogeneously distributed in the matrix. These composite materials have a high strength at ambient temperature; about 600 MPa with an ambient temperature ductility of 0.3-0.4% (plastic bend strain). The fracture toughness tests have shown that the composites have higher toughness than that of the matrix alloy. The zigzag cracks propagated in the composite, and the reinforcements TiB 2 and Ti 2 AlC particles and the fine grains of matrix were the main obstacles to the crack propagation.

High-Temperature Deformation of TiAl/Ti<sub>2</sub>AlC Composites Produced by Reaction Milling

High-Temperature Deformation of TiAl/Ti<sub>2</sub>AlC Composites Produced by Reaction Milling