Banca de DEFESA: CELMO HUDSON REIS DE PAULA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : CELMO HUDSON REIS DE PAULA
DATE: 29/04/2026
TIME: 10:30
LOCAL: meet.google.com/vsp-zbdd-qdx
TITLE:

EFFECT OF THE CARBON CONTENT ON THE MICROSTRUCTURE AND PROPERTIES OF NBC-FE / NBC- FENI

KEY WORDS:

Niobium carbide; Nickel; Iron; liquid phase sintering; Carbon.

PAGES: 91
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUMMARY:

The aim of this work was to correlate the overall carbon content in NbC-Fe / NbC-FeNi starting powders with the resulting microstructure, hardness and fracture toughness of Fe-bonded NbC cermets prepared by conventional liquid phase sintering for 1 h at 1400°C in vacuum. In the NbC–Fe system, the calculated carbon content ranged from 9.29 to 11.53 wt.%, being adjusted through the partial substitution of NbC with NbH₂ or graphite powders. In the NbC–FeNi system, the variation ranged from 9.25 to 11.48 wt.%, following the same approach for stoichiometric ratio adjustment. SEM microstructure analysis showed that, in the NbC-Fe system, the increase in carbon content promoted grain refinement of up to 76.5%. In the NbC-FeNi system, microstructural refinement was also observed, but with a larger average grain size and higher dispersion (standard deviation) compared to the iron-bonded system. Regarding phase composition, determined by XRD, the NbC-Fe system was described as consisting exclusively of cubic NbC and an FCC binder phase. In contrast, the study of the NbC-FeNi system evidenced the presence of the secondary Nb6C5 phase in lowcarbon samples, which disappears in compositions close to stoichiometry. Thermal behavior indicated eutectic temperatures as low as 1163 °C for the NbC-Fe system, while in the NbC-FeNi system, these temperatures ranged between 1384 °C and 1248 °C, decreasing as the carbon content increased. Regarding mechanical properties, the maximum Vickers hardness obtained was 11.8 ± 0.3 GPa for the NbC-Fe, which is higher than the 10.8 ± 0.5 GPa observed for the NbC-FeNi. On the other hand, the Palmqvist fracture toughness reached 7.0 ± 0.9 MPa⋅m 1/2 in the NbC-Fe system, being inferior to the 8.6 ± 0.5 MPa⋅m 1/2 of the NbC-FeNi system, which indicates the positive effect of nickel addition on the toughening of the material. Finally, the NbCFeNi system presented superconducting behavior, with diamagnetic transitions observed between 8.5 and 8.9 K in samples with higher carbon content. The influence of the carbon content on the sinterability, carbide grain size, morphology, and cermet mechanical properties were elucidated. A lower carbon content resulted in the aggregation of NbC grains and an increased mass transfer rate, resulting in coarser NbC grains. With an increase in carbon content in the system, the carbothermal reduction of surface oxides occurred at lower temperatures, resulting in better sinterability, improved binder distribution and a refined microstructure with superior mechanical properties compared to lower carbon content cermets.

COMMITTEE MEMBERS:
Externa à Instituição - ARIADNE DE SOUZA SILVA - UFRN
Externo à Instituição - MARCELLO FILGUEIRA - UENF
Interno - 2414250 - MEYSAM MASHHADIKARIMI
Presidente - 1350249 - RUBENS MARIBONDO DO NASCIMENTO
Interno - ***.121.804-** - UILAME UMBELINO GOMES - UFRN