Reaction Mechanism And The Electronic Structure Of Ti(C_1-xN_x) Materials By Self-propagating High Temperature Synthesis Ti-C-N₂ System

In this paper, we have investigated the reaction mechanism of the self-propagating high-temperature synthesis, and the influence of the content of Ti/C atomic ratio compacting pressures and diluents contents on SHS synthesis phase composition, microstructure in Ti-C-N2 system through experiment. Then influence of different x values on Ti(Ci1-xNx) mechanical properties and electronic structure through first principle, has been investigated detailedly.(1)By means of Ti-C-N2 system observation of self-propagating high temperature synthesis reaction process,after laser ignition sample was found that combustion waves spread rapidly to the bottom with severe heating phenomenon accompaniedly.After sintering the sample was crispy,we can see the sample has more pore from inside the fracture.(2)Result showed that the influence of process parameters on combustion synthesis of Ti(C1-xNx) materials was very important.With the decrease of the Ti/C radio,the carbon content increases and the nitrogen reduces in the Ti(C1-xNx) products.But smaller Ti/C radio will cause too much free carbon,while excessive Ti/C radio will cause the micro crack.The compacting pressure of sample is so small that it would cause the fly fracture and crack phenomenon in the combustion process.The compacting pressure is too great that it would hinder the reaction degree of nitride. Adding some diluents TiN in reaction raw material is beneficial to reduce the adiabatic temperature of the system and increase the degree of nitride product. Optimizating processing parameters,namely,when addition of TiN diluents was 20%,Ti/C radio was between 0.3mol and 0.7mol,and compacting pressure was 50%,the performance of Ti(C1-xNx) materials was the best.(3) The reaction mechanism of SHS is thoroughly investigated by combustion front quenching technique in the Ti-C-N2 system. Reaction can be divided into the following several stages:Firstly,sample is lit by the heat that system gives off,themolten Ti liquid package in Cparticle surface,form Ti solid solution containing carbon;secondly,N2 reach the surface of the solid solution by diffusion and internal,reacting with Ti generated Ti2N and TiNo.26 non equlilibrium phase;thirdly,the resulting in the middle of the carbon with Ti solid solution reaction Ti(C1-xNx) particles.(4) It is found by the calculation of first-principles of Ti(C1-xNx) material mechanical properties and electronic structure. The calculated cohesive energies shows that TiN has the highest structural stability. The calculated Elastic contents shows that the five phases are brittle and among the five phases TiC is a phase with the best plasticity. Then based on DOS, we reveal that the five phases all have the conducting properties. the covalent bonds are generated interactionally by the C(p)’s and N(p)’s electrons with the Ti(d)’s electrons.