Effect of nickel addition on the exothermic reaction of titanium and boron carbide
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Exothermic reaction path of the Ni–Ti–B4C system in the differential thermal analysis apparatus proceeded in such a way that Ni initially reacted with B4C and Ti to form Ni–B compounds and Ti2Ni with heat release, respectively; subsequently, the formation of Ni–B eutectic liquid between Ni2B and Ni4B3, and the appearance of Ni–Ti eutectic liquid phase between Ti2Ni and Ti were followed, which enabled the diffusion of Ni, B, C, and Ti in solution to form Ni–Ti–B–C liquid more easily and quickly at a low temperature; finally, TiC and TiB2 were precipitated out of the liquid. The addition of Ni provided an easier route for reactant mass transfer and accelerated the occurrence of complete reaction.
I. INTRODUCTION
Titanium diboride and titanium carbide possessed many desirable properties such as high hardness, low density, high melting temperature, high electrical conductivity, and high corrosion resistance, which constituted an excellent choice for applications in the high performance cutting tools and abrasives, wear-resistant parts, and armored vehicles.1–3 Traditional synthesis and fabrication methods of titanium diboride and titanium carbide included powder metallurgy, mechanical alloying, reactive sintering, and self–propagating high temperature synthesis (SHS) and so on.4–15 Among these fabrication technologies, the SHS technology was attached to much attention, due to its low energy consumption, high time efficiency, and high product purity.3 In general, the ignition of SHS reaction was controlled by the rate of surface reaction among reactants, which, in turn, was determined by the contact surface area among them. Thus, the formation of liquid and its subsequent capillary spreading were essential to the ignition and the propagation of the combustion wave because it substantially increased the contact surface area among reactants and provided an easier route for reactant mass transfer.16 However, in the Ti–B4C system, the melting point of Ti was so high that the melting of Ti needed excessive energy. Thus, the thought occurred that a SHS reaction may be significantly affected by forming an eutectic liquid at a low temperature
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0010 J. Mater. Res., Vol. 22, No. 1, Jan 2007
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with the addition of a low–melting–point metal, if the formation of the eutectic liquid can increase the contact surface area among the reactants and provide an easier route for mass transfer. Because the liquid Ni formed with solid TiC and TiB2 for the low wetting angle under vacuum at 1450 °C,17 nickel was selected as the additive metal, which not only accelerated the reaction rate, but also improved the abrasive wear and structural applications. However, in the combustion synthesis of TiC and TiB2, due to the high temperatures and velocities of reactions, it is difficult to understand the mechanism of SHS processes. As a result, an attempt has been made to investigate the effect of nickel on th
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