Fabrication and characterisation of in-situ metal matrix composites

Thanks to their ductile matrix and hard ceramic reinforcement phases, metal matrix composites exhibit properties such as high abrasion resistance, strength and hardness. These properties provide MMC's to be used in wide range in aviation, space and manufacturing industries. Within the scope of the thesis, formation of in-situ Fe-TiC, Fe-TiB2 and Fe-TiC-2TiB2 metal matrix composites via volume combustion synthesis (VCS) were investigated with using Fe-Ti-C, Fe-Ti-B and Fe-Ti-B-C starting powder mixtures respectively. The reactant mixtures were heated via different heating sources/procedures (Vacuum induction furnace (VIF), TIG torch (TIG), Tube type furnace (TTF)) for the formation of the composites. Vol. % 15-90 reinforcement phase were investigated for all systems. In order to understand reaction mechanisms of the all systems better, Fe-Ti, Fe-B, Fe-C, Ti-B, Ti-C and Ti-B-C systems were also investigated. Gibbs free enegy and adiabatic temperature calculations of the reactions in the systems were made. Optical microscope, SEM examinations, EDS and XRD analyses, microhardness and three-point bending measurements were used for characterisation. Thus, ignition, reaction mechanism of the investigated systems and microstructure and microhardness properties according to different heating methods were determined. While particle formation was occurred in the VIF and TIG samples via VCS, there was no VCS in TTF samples and particle formation was limited. It was understood that more than 1200oC which is applied heating temperature was required for the formation of the particles via VCS in TTF samples. According to the characterisation results, it was considered that ignition and the exhotermic reaction between T and C in the Fe-Ti-C system was occured via FeTi+Fe eutectic liquid. I was considered that the ignition and reaction mechanisms of Fe-Ti-B and Fe-Ti-B-C systems were similar to Fe-B and Ti-B systems and reactions between Fe-B and T-B play role in the ignition of these systems. It was understood that due to the C loss, a reaction was occurred between Fe and Ti which was remained from TiC formation. Single Fe phase was provided in the samples via increasing starting amount of C. It was shown that Fe2Ti and Fe3C are not necessary side products in occuring of the Fe-TiC composites. It was seen that microhardness and particle sizes of the composites were increased with a rise in the reinforcement amount. Microhardness values of the VIF samples were measured between ~305-1268 HV0,2 for Fe-TiC composites, ~390-2166 HV0,2 for Fe-TiB2 composites and ~274-2074 HV0,2 for Fe-TiC-TiB2 composites. Particle sizes on the other hand, is between ~0,68µm-3,18µm and ~0,21-3,37µm for the Fe-TiC and Fe-TiB2 composites respectively. The particle sizes of the samples that were heated via TIG torch were higher than the samples which were heated by VIF. The microhardness values of the VIF samples that have relatively thinner particles is higher than the TIG produced samples which have coarser particles for the Fe-Ti-C and Fe-Ti-B systems. It was shown that providing the production of in-situ MMCs in the selected systems via appliying VIF and TIG heating in this work. It was suggested that TIG heating is a much more practical method for this application.