Fabrication of TiB 2 /Al composite by melt-SHS process with different content of titanium powder
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Melt-SHS (self-propagating high-temperature synthesis), based on the SHS process and oxide reaction method, was used for preparation of TiB2/Al composites. The mass ratio of two reactants, Ti powder/TiO2, in initial powder mixture was varied from 0:1 to 1:0. The results showed that the 5 wt% TiB2/Al composites could be successfully produced by a reaction of aluminum powder, TiO2, and B2O3 in Al melt at 950 °C, while the reaction rate was slow. The addition of titanium powder helps to reduce the content of Al2O3 and destroy the coating structure of Al2O3 covered TiB2 particles, which leads to the acceleration of reaction process and improvement of particle concentration. A significant improvement was that TiB2 particles were dispersively distributed when the mass ratio of Ti powder/TiO2 was 2:3. As a result, the 5 wt% TiB2/Al composites fabricated by melt-SHS process with modified reactants ratio showed excellent tensile properties with the ultimate tensile strength as high as 114.24 MPa. Besides, the composite also showed superior ductility.
I. INTRODUCTION
In situ particulate reinforced aluminum matrix composites (Al MMCs) are widely used in the aerospace and automotive industries due to their excellent properties, such as high specific strength, low weight, and chemical inertness.1 It consists of matrix and the reinforcement, and the reinforcement is one of the most important parts. TiB2 particles reinforced Al MMCs is one of the most widely used particulate reinforced Al MMCs because of its outstanding properties, such as low density, high melting point, high elastic modulus, and good lattice matching relations with the aluminum matrix.2 It has been reported in many studies that TiB2 particles can be synthesized by in situ synthesis method, and the process offers significant advantages over the conventional processing from both technical and economic standpoints,2,3 such as its excellent interfacial compatibility between matrices and reinforcements, thermodynamically stable, and distribution uniformity of the reinforcements in the matrix. In situ TiB2 particles reinforced aluminum matrix composites can be synthesized by the salt-metal reaction, self-propagating high-temperature synthesis (SHS), hot pressing, pressureless sintering, and mechanochemical synthesis.3,4 The salt-metal reaction is the most commonly used in situ methods.5 In this processing, the Contributing Editor: Michele Manuel a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.184
mixed K2TiF6 and KBF4 were used as reactants, which reacted with molten Al at a high temperature to form TiB2 particles in the Al matrix.6 However, the method has fluoride emissions and the dross needs to be disposed. As one of the fabrication techniques to synthesize in situ ceramic particulate reinforced MMCs, SHS technology has received much attention because of its low energy consumption and high product purity. Nevertheless, the price of the reactants is expensive, and procedure is complicated and time consuming because the final
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