Investigation Of Reaction Behavior And Products Of Combustion Synthesis From Cu-Ti-C System Under The Participation Of Air

Titanium carbide (TiC) has become an attractive compound as a reinforcing phase due to its high modulus, high hardness and high melting temperature, and copper has also become an attractive material matrix because of its good electrical, thermal conductivity and good ductility. TiC reinforced Cu matrix composite (TiC/Cu) exhibits both excellent performances of TiC and Cu, which make it a potential material for the wide application such as being applied as the electrical, thermal conductivity materials and wear resistant materials. Therefore, wide-spread attention has been paid on this composite. In the 1960s and 1970s TiC ceramic particles were added in Cu matrix to fabricate Cu matrix composite exhibiting high strength and high temperature resistance. With the development of composites, TiC/Cu was studied gradually. However, it was shown that wettability between copper and TiC ceramics is so poor that copper matrix composite was difficult to produce. This poor wettability is responsible for preventing the incorporation of TiC ceramic phase into copper. In recent years, a much higher demand has been requested for the research and production on new materials, and thus a large amount of research is needed for TiC composite and its processing.In situ combustion synthesis has many attractive advantages, such as high purity of products, low processing cost, and energy and time efficiency, no high-temperature furnace process, non-polluting traits, etc. Since 1960s, in situ combustion synthesis has become a very important technique for material synthesis and processing. Two modes are included in combustion synthesis, self-propagating high-temperature (SHS) and thermal explosion (TE), both of which have been widely applied in the material fields. SHS is the mode that the perform is ignited from one end, while TE is the one that the whole perform is heated to the ignition temperature and then thermal explosion occurs through the whole body, ending in an instant.Compared with other processing techniques, in situ combustion synthesis used for the fabrication of TiC/Cu has several merits as follows:(1) Simple processing equipments and machines, short processing period and high production rate. Moreover, it has a high reaction speed. For example, TE needs only several seconds to complete, and the SHS combustion wave can transmit at a speed of 250mm/s.(2) Short synthesis production cycle and the great reduction of the cost.(3) Because combustion synthesis can use for Hear Net Shape (NNS) technique, consumption of reactant is decreased greatly.(4) The reaction temperature of combustion synthesis can reach 4000K, and the heating rate of the exothermic reaction is up to 104-106K·s-1. In SHS reaction, the temperature gradient is up to 10⁵-10⁶Km^-1. The combustion synthesis has a high temperature in the synthesis reaction, so it can synthesize high purity products. At the same time, such a high heating and cooling rate can obtain the products with the non-equilibrium structures.This paper mainly aims to investigate the reaction process of forming TiC particulates via DTA of Cu-Ti-C system under the protection of Ar or in the air. Moreover, the effects of Cu content, and the size of C as well as Ti particulates are investigated detailedly in TE combustion synthesis modes. The main results of the present study are as follows:(1) According to the calculation of thermodynamics, the reaction of Cu + Ti+C→Cu+TiC is favorable and the formation of TiC is stable under the protection of Ar. So it is feasible to use Cu, Ti and C particles to fabricate TiC/Cu. In the air, the change of Gibbs free energy (ΔG⁰) is negative in both 2C + O₂→2CO and Ti + 2C O→TiC+CO₂ reactions. The reactions can also occur according to the thermodynamic theory. The Change of enthalpy as temperature for TiO₂ is the most negative, so the exothermal reaction is the most. The exothermic reaction of Ti + 2CO→TiC+CO₂ is bigger than the reaction of Ti + C→TiC.(2) In 20wt.% Cu -Ti-C system, under the protection of Ar, the reaction process of fabricating TiC particulates via DAT reaction is as follows. First, Cu-Ti intermetallic compounds are formed though solid-state diffusion reactions of Cu and Ti particles. The Cu-Ti liquid phases are formed when the temperature reaches the eutectic point. This reaction accelerates the formation of TiC. With the increase of temperature, the C particles are packed in Cu-Ti intermetallic compounds, which accelerate the solid solution of more C particles in Cu-Ti intermetallic compounds. The TiC particles continue to precipitate out and grow from the Cu-Ti-C liquid phase. The carbon black can more accelerate the solid solution. In the air, with the increase of temperature, the Cu_xO_y, TiO₂, TiN, TiC and C_0.3N_0.7Ti phases are formed in turn. But the amount of TiC particles is very small. Carbon black have reducing more strongly, so the product have no CuO.(3) It has been shown that the SHS reaction. With the increase of C particle size, the sizes of TiC particulates decrease.(4) In the TE equipment, compared with the TE reaction under the protection of Ar, the TE reaction occurrs more easily in the air, and the reaction products consist of TiC and Cu phases. The ignition temperature of TE reaction in the air is lower than that under the protection of Ar, which may be due to the participation of oxygen in the air.(5) The TE reaction in the air, the reaction products of Cu(44μm)-Ti(28μm)-C(<1μm) system consist of TiC and Cu. With the Cu content increasing from 10 to 90 wt.%, the ignition temperature of the Cu-Ti-C system increases and the time of reaction is prolonged. With the decrease of Ti and C particle sizes, the ignition temperature of the Cu-Ti-C system decreases. With the decrease of C particle sizes, the size of TiC particulates also decreases. The size of Ti particle has little influence on the TiC particles size.