Synthesis Mechanism And Preparation Of Electric Field-activated FGM

There are many defects such as incompletable reaction and impurity etc. being observed when low exothermal reaction systems composite materials were prepared by traditional Self-propagating High-temperature Synthesis (SHS). When an electric field was exerted, which could be eliminated by the Joule heating and mass transfering effects to overcome the thermodynamic and kinetic limitations of SHS and make the reaction continuing. In this paper, electric field-activated self-propagating high-temperature synthesis (FASHS) was applied to prepare TiC-Ni-x%Fe and TiC-Al2O3-x%Fe systems functional gradient materials (FGM), which could be applied in the field of navigation, spaceflight, machine industry and so on.The test materials were selected and matched according to the application of FGM to meet the requirement of mechanical properties in various service conditions. In the test, the reaction stocks were prepared by filling and impacting reactants layer-by-layer in bothway. And the synthesis reactions of singlelayer uniform reactants and multi-layer gradient reactants were compared that were carried out under the condition of exerting or non-exerting electric field respectively.The optical microscope, SEM and X-ray diffraction were applied to study the microstructure and phase of products. At the same time, the surface hardness and microhardness of synthetic materials, as well as the velocity of reaction wave of single layer and multi-layer reactants were tested.The component and microstructure of TiC-Ni- x%Fe systems FGM, which was prepared by FASHS, changed continuous and uniformly as gradient, and no cracking and cavity were observed in the joining interface; the component and microstructure of TiC-Al2O3-x%Fe systems FGM prepared in the same way changed discontinuously as gradient, and no cracking and cavity were observed in joining interface.It was indicated that the hardness of TiC-Ni-x%Fe and TiC-Al2O3-x%Fe systems FGM decreased in gradient with the increase of Fe when E was 20V/cm and 16V/cm respectively. The effects of Joule heating and ionic electromigration made the concentration difference of elements in the joining layer decreased during the preparation of TiC-Ni-x%Fe and TiC-Al2O3-x%Fe systems FGM. As a result, the average grain size of TiC-Ni-x%FeFGM was decreased, and the finest griain size was about 0.1 ~~0.45 u m. The density and hardness of FGM could be increased obviously when the pressure was exerted in high temperature stage after the reaction finished.The combustion model of single-layer reactant was studied by quenching test and the one of gradient-layer reactants was established according to the result that the wave velocity of TiC-Ni-10%Fe is the greatest, which offered the reference for further study of the actuating time of electric field when FASHS was applied to preparae FGM.