چكيده به لاتين
Producing new materials with unique properties and applications, including composite materials, ensures the progress in engineering sciences. Among different types of composites functionally graded composites (FGM) have received attention in recent studies. In this research, the possibility of producing layered, functionally graded Ni/NiTi/TiC composites using the combustion synthesis process was studied. The effect of various parameters such as Ni and Ti particle size as well as effect of the presence of NiTi interlayer on porosity of different layers, microstructure, and hardness of the produced composite has been discussed. Elemental Ni and Ti powders along with graphite were cold-pressed to prepare samples consisting of five layers (with NiTi intermediate layer) or four layers (without NiTi interlayer) with different chemical composition in each layer (from pure nickel to Ti + C rich layer) and different grain sizes of Ni and Ti. Then the samples were synthesized in an induction furnace to perform high temperature self-propagating, high-temperature synthesis by provoking the exothermic reactions in different layers. The analysis of the synthesized samples showed that the combustion synthesis was done completely in the samples with fine and medium grain size of reactant, but with increasing particle size, the combustion synthesis was not completed and some unreacted elements were found in the samples. X-ray diffractometry (XRD) and electron microscopy (SEM-EDS) analysis shoowed that the phases present in most samples were Ni and TiC as well as the intermetallic phases NiTi, Ni3Ti, Ti2Ni. The percentage of porosity in the samples was affected by the particle size of the reactant elements. As Ni grain size decreased, the reaction rate and consequently the porosity increased. By increasing the percentage of Ni throughout the sample, the particle size of titanium carbide particles decreased and their morphology became more spherical. Also, the increase of Ni in different layers led to a decrease in combustion temperature in Ni-rich layers and also a decrease in hardness, so that in the titanium carbide rich layer, the hardness number reached 1400 Vickers and in the Ni-rich layer, the hardness number was reduced to about 300 Vickers.
