Reaction Mechanism And The Electronic Structure Of Cu-Ti-Si System By Self-propagating High Temperature Synthesis

The intermetallic compound of Ti5Si3been worthy of in-depth study, in view of its high melting temperature (2130℃), low density (4.32g/cm3), high hardness (11.3GPa),etc. At the same time, the trends of the industrial development can be reduced to the saving of energy and resource. Self-propagating high temperature synthesis technique have strong application in intermetallic compounds, this method has the characteristics of energy saving, convenient.In this paper, we have investigated the reaction mechanism of the self-propagating high-temperature synthesis, and the influence of the content of Cu, Ti/Si atomic ratio on SHS synthesis products of combustion temperature, phase composition, microstructure in Cu-Ti-Si system through experiment. Then influence of Cu addition on Ti5Si3mechanical properties and electronic structure through first principle, has been investigated detailedly. It can be provided that the valuable theoretical foundation of SHS in Cu-Ti-Si system. The major research efforts of the present study are as follows:(1)It is observed SHS process of Cu-Ti-Si system through experiment. It is found that local lighting on the compact surface in preheating stage, combustion wave spreads to compact rapidly and emits intense light and heat in reaction stage, the temperature of the compact is reduced instantly and end of the reaction in cooling stage; At the same time, results show that the combustion temperature significantly decreased with the increasing of Cu content, and combustion temperature increased with the increasing of Ti/Si atomic ratio in Cu-Ti-Si system. Compared with the Cu content, Ti/Si atomic ratio has little effect on combustion temperature.(2)It is found that the content of Cu and Ti/Si atomic ratio have affected on phase composition and the microstructure of the SHS products by means of XRD, SEM and EDS. Results show:the phase composition of products in the reaction considerably is formation of non-stoichiometric, but be still considerably is relative to the initial stoichiometric ratios of reactants with different Ti/Si atomic ratios. Meanwhile, it can be seen that the morphology of the products are not the same with different Ti/Si atomic ratios, TiSi2phase exhibits strip, TiSi exhibits irregular polygonal, and cobble-stone of Ti5Si3. Furthermore, the main phase of product is Ti5Si3with different Cu contents in Cu-Ti-Si system, but TiSi2, Cu3Si, Cu9Si of non-stable phase still exist.Then the porosity of products decrease gradually with Ti/Si atomic ratio and the Cu content increasing, density of products gradually increased. Meanwhile, it is found that the particles appear a large number of liquid with Cu addition, promote the reaction, and improve the adhesion method of the particles.(3)The reaction mechanism of SHS is thoroughly investigated by combustion front quenching technique in the Cu-Ti-Si system. It is found that Cu-Si eutectic liquid appear firstly in SHS process. When [Ti] and [Si] dissolve in the liquid phase, once reached saturation, Ti5Si3begins to precipitate in saturated liquid, and emit large amounts of heat, ignition combustion reaction. It puts forward that the phase formation of product is dissolution-reaction-precipitation mechanism.(4)It is found by the calculation of first-principles for Cu-Ti-Si system, results show Cu preferentially occupies4d-Ti position, and it reduces the relative stability of Ti5Si3, but improves the overall performance of Ti5Si3. It is found that the lattice constants a, c decreases with the Cu content increasing of Cu occupies4d-Ti position of Ti5Si3; And the bulk modulus B and shear modulus G gradually decreases, Cauchy pressure (C12-C44) and B/G value is increasing, suggesting that metal bond has formed in Ti5Si3with Cu addition, to make it the transition brittle materials from ductile materials, improving the overall performance of Ti5Si3.