In Situ Reaction Kinetics and Microstructure Evolution in Preparing Particle-Containing Copper Alloys by Mechanical Allo
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NANOCERAMIC particles of dispersion-strengthened copper alloys remain of interest as high-temperature structural and functional materials for industrial applications because of their reasonable high strength combined with good ductility and excellent conductivities.[1,2] To date, a considerable effort has been devoted to the development and processing of novel dispersionstrengthened copper alloys as well as the improvement of their mechanical and physical properties.[1–17] Many kinds of fine ceramic particles, i.e., oxides, borides, carbides, and nitrides, and many different in situ or ex situ preparation methods or techniques have been used to strengthen the pure copper matrix. Because of their excellent microstructure and properties, these kinds of advanced materials have been widely used as contacts, lead wires, electrodes, vacuum technique parts, and electrical conductors employed at high temperatures and in nuclear reactors.[6–13] To obtain the excellent mechanical and physical properties, the main structural requirements for dispersion-strengthened copper alloys are a homogenous distribution level and thermodynamic stability of nanoparticles in the copper matrix. Compared with other MINGXING GUO, Associate Professor, and FEI WANG, YAN ZHANG, and XUKAI ZHANG, Graduate Students, are with the State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected] Manuscript submitted July 9, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
ceramic particles, TiB2 is an advanced and excellent ceramic material, which demonstrates specific physical and mechanical properties, i.e., relatively high melting temperature [3498 K (3225 C)], high hardness (3400 Kgf/mm2), high elastic modular (574 GPa), and better electrical conductivity (10–5X cm). The thermodynamic stability of TiB2 can result in the extremely low residual content of Ti and B in copper matrix. Therefore, it is a good choice to use TiB2 particles to strengthen the copper matrix. But the poor wettability between TiB2 particles and copper melt normally causes the serious aggregation of TiB2 particles in the copper matrix, and it is impossible to synthesize dispersionstrengthened Cu-TiB2 alloys by stir casting or any other mechanical mixing routes.[14] To date, although several different methods have been developed to prepare Cu-TiB2 alloys, such as the ex situ mechanical alloying (MA),[11–13] carbothermic method,[14] spray deposit,[15,16] self-sustaining reaction,[17] and in situ reactionrapid solidification technique,[5,18] all of them have their own shortcomings in the preparation process or their further applications. If we take the short-flow technique combining in situ reaction with rapid solidification shown in References 5 and 18 as an example, then we can find that, although the short-flow technique can be used to prepare different concentrations of Cu-TiB2 alloys, with the increase of Ti or B solute concentration, it is difficult to avoid the coarsening and ag
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