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- Microwave versus Conventional Sintering of NiTi Alloys Processed by Mechanical AlloyingPublication . Teixeira, Rodolfo da Silva; Oliveira, R. V.; Rodrigues, Patricia Freitas; Mascarenhas, João; Neves, Filipe; Paula, Andersan dos SantosABSTRACT: The present study shows a comparison between two sintering processes, microwave and conventional sintering, for the manufacture of NiTi porous specimens starting from powder mixtures of nickel and titanium hydrogenation-dehydrogenation (HDH) milled by mechanical alloying for a short time (25 min). The samples were sintered at 850 degrees C for 15 min and 120 min, respectively. Both samples exhibited porosity, and the pore size results are within the range of the human bone. The NiTi intermetallic compound (B2, R-phase, and B19 ') was detected in both sintered samples through X-ray diffraction (XRD) and electron backscattering diffraction (EBSD) on scanning electron microscopic (SEM). Two-step phase transformation occurred in both sintering processes with cooling and heating, the latter occurring with an overlap of the peaks, according to the differential scanning calorimetry (DSC) results. From scanning electron microscopy/electron backscatter diffraction, the R-phase and B2/B19 ' were detected in microwave and conventional sintering, respectively. The instrumented ultramicrohardness results show the highest elastic work values for the conventionally sintered sample. It was observed throughout this investigation that using mechanical alloying (MA) powders enabled, in both sintering processes, good results, such as intermetallic formation and densification in the range for biomedical applications.
- Investigation of the Effect of Milling Time on Elemental Powders of Oxi-Reduction Nickel and Hydrogenation : Dehydrogenation TitaniumPublication . Teixeira, Rodolfo da Silva; Gurgel, Mônica Aline Magalhães; Rodrigues, Patricia Freitas; Freitas, Bruno Xavier de; Le Sénéchal, Naiara; Oliveira, R. V.; Neves, Filipe; Paula, Andersan dos SantosABSTRACT: Mechanical alloying (MA) is widely applied in the synthesis of blended elemental or prealloyed powders. This work evaluates the effect of milling time on elemental nickel and titanium powders produced by oxi-reduction and the hydrogenation-dehydrogenation process, respectively. The powders are characterized by scanning electron microscopy, X-ray diffraction, particle size, powder yield, and differential scanning calorimetry. It is observed that increasing the milling time promotes the formation of a structure composed of thin lamellae of nickel and titanium, which results in the beneficial effect of lowering the temperature for the formation of the intermetallic of the Ni-Ti system and in the powder yield achieved. The reduction of milling time in the MA process of NiTi alloys enhances technological efficiency by decreasing their overall processing time.