Percorrer por autor "Rafiaei, Seyed Mahdi"
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- Synthesis of (Ti, W, Mo) CN based cermets with different carbides configurations for demanding applications: Study of the crystal structure, microstructure, and mechanical propertiesPublication . Rafiaei, Seyed Mahdi; Hadi, Morteza; Fernandes, F.; Fernandes, FilipeIn this study, based on different element configurations within constant atomic ratio of elements, (Ti0.93W0.07Mo0.07)C–20%Ni and (Ti0.93W0.07Mo0.07)CN0.3-20%Ni derived cermets have been synthesized. The basis for the difference in the production route was whether the carbides were formed by carbothermic reaction from the metal oxide together or separately, or in the case of Mo2C, the carbide is added to the mixture together with the binder after reduction and just before consolidation. Another basis for the difference was whether the cermet was a carbide or a carbonitride. To investigate the influence of the different production routes, the crystal structure, microstructure, and mechanical properties of the cermets produced were examined using XRD, FESEM, STEM, and Vickers indentation. The XRD spectra of all the cermets were found to be very similar to those of TiC-based cermets, indicating that the additive carbides in the TiC or Ti(CN) phases of the cermets dissolve perfectly during the high vacuum sintering process at 1510 °C. The highest toughness (14.65 MPa m1/2) was obtained in (Ti0.93W0.07) C–8%Mo2C–20Ni cermets with a core-rim structure. In addition, the use of nitrogen leads to a dramatic reduction in particle size. The use of molybdenum and tungsten in the form of separate carbides had little effect on limiting the expansion of crystal size and grain size compared to the scenario where the dissolution of these elements took place within the primary core-rim structure. However, in terms of hardness and toughness, it was found that, in addition to grain size, the route taken in the addition of molybdenum and tungsten was also important.
- The effect of Mo2C additions on the oxidation resistance of (Ti,W)CN cermets as base material for the production of cutting toolsPublication . Hadi, Morteza; Rafiaei, Seyed Mahdi; Fernandes, FilipeThe effect of Mo2C secondary carbide on the oxidation resistance of (Ti0.93W0.07)CN0.3-20%Ni cermet was investigated using DSC-TG, isothermal oxidation, XRD, and SEM/EDS characterisations. Adding Mo2C secondary carbides to (Ti, W)CN cermets is one of the methods used for improving their mechanical properties. However, Mo2C secondary carbides bring a detrimental effect to oxidation resistance. The isothermal oxidation results of the samples at 750 ◦C possessing 0% and 2% MO2C follow the parabolic law, while in the samples containing 5% and 8% Mo2C, the rate of oxidation and the spallation of the oxide scale increased significantly. The thickness of the oxide layer in the cermet containing 5% of Mo2C increased three times, whereas the mass per unit area of the detached oxides in the 8% Mo2C specimen dramatically increased up to 100 times. The investigations revealed that the increase in the amount of W and Mo on the cermet material, as well as the formation of a multi-zone oxide layer, are the main reasons for oxide phase propagation.