| Field Activated and Pressure Assisted Synthesis, FAPAS, as a new process that is carried out in the condition of multi-fields including electric field, mechanical field, temperature field and chemical field, has become one of key technologies to prepare heat-resisting bulk materials with nano-structure for its characterization of high temperature, fast heating-up, efficiency and energy saving. A new approach is brought forward by the mechanical alloying assisted FAPAS process (MA-FAPAS) to have cermets in-situ synthesized and diffusion bonded with metals simultaneously.MA-FAPAS was employed to prepare (TiB2)pNi/Ni3Al/Ni ,(TiC)pNi/TiAl/Ti and (TiB2-TiC)pNi/TiAl/Ti joining structures by diffusion bonding and in-situ synthesis with Ni3Al and TiAl as exothermal media layer, respectively. The effect of different reaction system, temperature and current on the combustion synthesis and formation mechanism of the diffusion interfaces was analyzed. Thermodynamic properties of the different reaction systems were calculated based on the theory of the minimum Gibbs free energy. The microstructure and phases of each layer and the distribution of elements across the interfaces were determined by SEM, TEM, XRD, and EDS. The change of state of the atoms in interfaces was calculated by Thomas-Fermi equations under the action of the electric field. The hardness, tenacity, fracture toughness, and wear resistance of the surface of the synthesized gradient cermets were tested by means of micro-indent testing and friction testing. The bonding strength and thermal shock resistance were evaluated by the three-point bend testing, shearing testing and quenching testing, respectively. The residual stress in the boding interfaces was simulated by ANSYS finite element method.It is concluded that the adiabatic temperature Tad and Gibbs free energyΔG increase with T0 for Ni-Al, Ti-Al, Ni-Ti-C and Ni-Ti-B4C reaction systems, and it is feasible to obtain the target products by combustion synthesis. It is necessary to preheat not less than 600K, 450K, and 600K for Ni3Al, TiAl, and 50wt%TiC-Ni reaction systems, respectively, and that would be less when the electric field was applied.During the combustion synthesis, the powder elements for synthesis of the gradient cermets of (TiB2)PNi, (TiC)pNi and (TiC-TiB2)pNi get reacted completely to form compact products and no interface is observed between the gradient layers. The element powder mixtures of Ni-Al and Ti-Al with stoichiometric ratio got reacted completely to form Ni3Al and TiAl intermetallic with equiaxial polygonal grains and got bonded with the metal plates and gradient cermets well, respectively. The EDS analysis results showed that the elements across the interfaces distribute in grade by intense diffusion to each other.It is concluded by the diffusion kinetics that the temperature, current and time are the most important factors that determine the microstructure of the interfaces during the diffusion bonding. The thickness of the diffusion interfaces between Ni/Ni3Al and between TiAl/Ti increases with the current and time and its square root is in exact ratio to I2·t. Under the action of the electric field and temperature field, the movement of atoms in the interface is controlled by the lattice diffusion mechanism mainly at first and then shift to interface reaction mechanism and then to grain boundary diffusion mechanism. The coefficient of diffusion of the atoms increases and the activation energy of diffusion in the interfaces decreases with the increase of current and time during the diffusion bonding process.The effect of the electric field on the diffusion of TiAl/Ti bonding interface is stronger than that of Ni3Al/Ni bonding interface. The current promotes the atoms to migrate across interface by increase their kinetic energy. The direction of the current had different effect on the migrating of Al atom in the interface between Ti/TiAl/Ti.The results of the mechanical properties tests indicate that the in-situ synthesized cermets own excellent surface hardness, wear-resistance, and fracture toughness. The interfaces of the bonded structures had higher shearing strength and that of the (TiC)PNi/TiAl/Ti reaches to 70.98MPa.The analysis results of the residual stress of the samples simulated by ANASYS shows that the existence of the media layer of the intermetallic compound lowers the differences of the deformations between the layers. The mismatch rate of the coefficients of thermal expansion are 132.1%, 10.8% and 47.2%, respectively, and corresponding equivalent stress are 38.74MPa, 10.51MPa and17.93MPa。...
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