| Summary: | 碩士 === 大葉大學 === 機械工程研究所碩士班 === 92 === The self-propagating high-temperature synthesis (SHS) of three NiTi, Ni3Al and Ni3Al+B intermetallic compounds was studied. Effects of initial sample density, preheating temperature, and particle size of the reactants on the flame-front velocity, combustion temperature and composition of combustion products were investigated. The influence of preheating the sample prior to ignition on the synthesis process was also discussed. It was found that all these three kinds of SHS processes were characterized by the steady propagation of the flame front. The combustion process indicated the melting and shrinkage of test samples except for the compacts with low initial densities in the synthesis of Ni3Al, in which the volume expansion was observed. The flame-front propagation velocities increased with initial sample density and preheating temperature. The increase in boron concentration led to a noticeable increase in flame-front propagation velocity. The flame-front propagation velocities in this study were in the region between 5.5 and 121 mm/s. Based upon the measurement of flame-front velocity and combustion temperature, the activation energies of SHS processes associated with Ni3Al and Ni3Al+B systems were calculated to be 92.06~97.78 kJ/mole and 86.4 kJ/mole, respectively. The composition of combustion products was affected by the initial sample density, preheating temperature, and particle size of reactants. Results of X-Ray Diffraction (XRD) analysis indicated that in addition to the NiTi phase, the existence of NiTi2, Ni3Ti, and unreacted metal in the final products of the Ni-Ti system was detected. However, fully-reacted products made up of the Ni3Al phase were obtained in the Ni3Al and Ni3Al+B systems. The microstructures of synthesized products illustrated by Scanning Electron Microscope (SEM) photographs indicated the formation of high-density and porous NiTi compounds. In the synthesis of Ni3Al, the addition of boron resulted in the formation of denser products when compared with the condition without boron.
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