| Two new methods of materials preparation, such as self- propagating high-temperature synthesis (SHS) and mechanical alloying/milling (MA/MM) have been developed since 1970s. They have been applied extensively in material fields. High-exothermic reaction such as Ti and C can be activated by mechanically induced self-propagating reaction (MSR) mechanism. MA and SHS are combined into one new method MSR. In this experiment, nanocrystalline TiC, and TiC-dispersion-strengthened Cu-base composites have been prepared by MSR and MA methods. In this paper, the processes and the affect factors of the reaction of Ti and C by mechanically induced self-propagating reaction are described in details. The structural change, grain size, particle size, lattice parameter and changing rule of microstructure of elemental Ti and C powders during mechanical alloying have been studied by EPMA, X-ray diffraction and laser particle sizer. The results show that the TIC of nanocrystalline size (2Onm) and ultrafine particle (average particle diameter 5.64 urn) can be synthesized by MSR after about milled for 2h. The crystallite size of the TiC powers decreased, which can reach the value 7nm after milled for lOh, and the particle size of the reunited powders, which the average particle diameter increased to 40.61 urn after milled for 28h, with the increasing of the milling time. The lattice distortion was relatively low. The broadening of the diffraction peaks mainly ascribed to crystalline refinement. The lattice parameter of the just reaction TiC was bigger than that of standard TiC and decreased with subsequent excess milling. The products have porous character of the SHS products. The effects of ball to powder ratio, radius of ball, reactant ratio, process control agent and mill style on the reaction incubation time of kinetics were studied. It was found that the incubation time decreased with ball to powder ratio increased. When the density of balls and the ball to powder ratio were decided, the incubation time increased with the radius of ball increased. Cu-Ti-C powders mixed which Cu weight fraction was 80% were mechanically alloyed. At the initial stage of milling, Ti and C dissolved into Cu matrix and formed Cu-base supersaturated solid solutions. The Ti and C solute elements precipitated partially, took place reaction and formed the production of TiC after milling lOh by planetary mill. Powder and crystal refinement and the defects of subinterface and dislocation resulted from MA are main causes of formation of supersaturated solid solutions and the secondary phase precipitation. In the Cu-Ti-C system, the mechanism of milling took place change when the content of C doubled. The formed TiC could dissolve into Cu-base. The TiC could reprecipitate again with excess milling and Cu crystal decreasing. TiC-dispersion-strengthened Cu-based composite powders have been prepared from TiC-Cu and Cu-Ti-C mixed powders by MA. The composite powders were prepared into composite materials by pressing, sintering and heat-extrusion. The suitable sintering temperature of Cu-TiC system is 900 0C . The materials possessed uniform microstructure and better properties. Relative density, ductility and conductivity of these composite materials decreased with milling time prolonged and TiC weight fraction increased. But the performance on the mechanical behavior such as hardness, yield strength and tensile strength increased. When the materials of Cu- 2.Swt%T1C milled for... |
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