Study On The Microstructure And Properties Of Functionlly Gradient Materials Prepared By FAPACS

On the study, the functionally gradient materials (FGMs) of Ti-C-Ni and Ti-B₄C-Ni systems have been synthesized by field-activated and pressure-assisted combustion synthesis (FAPACS). The troditional Combustion Synthesis (CS) technology is widely used to prepare metal-ceramic composites because it has the characteristics of conserving energy, fast reaction and high product purity, But the technology has inherent characters of reactive incompletion as well as high porosity and defect during the formation of composite materials. However, under the applications of pressure and electric field, the relative density of materials is improved by FAPACS. The thermodynamic limitation of CS reaction is overcame by the mass transport effect and Joule heat, in order to obtain the high-density functional materials which will be widely put into areas of spaceflight and machine building.In this paper, take Ti-C-Ni and Ti-B₄C-Ni systems as investigation. The Gibbs free energy of systems is primarily calculated for analyzing the possibility of sustaining reaction during the combustion synthesis process of FGMs in theory and defining the theory evidence for experiments subsequently. The results are shown that, in order to make Tad increased and more than 1800K, Ti-Al system and composite ceramic layer with Ni content of 50% would be preheated to 500℃.In the experiment, scanning electron microscope, optical microscope and X-ray diffraction analysis have been applied to observe and determine the microstructure and phase of each layer, to investigate the distribution of the element across the interface. Mechanical property is well done by microhardness instrument, abrasion machine and SENB. The results show that the imposition of the electric field and the combustion reaction of TiAl is the key for the successful synthesis of functionally graded materials (FGMs) during process; the TiC particles formed by in-situ synthesis process were fine and distributed uniformly; concentration profiles of elements across the interfaces of the layers show significant inter-diffusion and good metallurgical bonding; moreover, the FGMs has gradient distribution of micro-hardness and toughness across the titanium substrate to the surface layer. In addition, the average value of KIC in surface layer of composite ceramic is about 3.6MPa·m^1/2, this layer be provided with excellent abrasive resistance, and the value of abrasion loss is 87% off than that of high speed steel.The study on diffusion bonding between Ti and TiAl plate with current applied show that pressure, current and diffusion time are identical factors to influence the performance of diffusion joint. When the current is up to 1200A, the SENB intensity of joint is 353MPa; when the diffusion bonding, between Ti substrate and Ti-Al mixture powder, with current applied under the pressure of 40MPa, the diffusion dissolution layer is obviously divided into two parts, Ti(ss.Al) and (Ti3Al+TiAl), and its width and mechanical property are all increased with increase of current and diffused time.