Banca de QUALIFICAÇÃO: MURILLO MENNA BARRETO DE MELLO JUNIOR

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : MURILLO MENNA BARRETO DE MELLO JUNIOR
DATA : 08/06/2018
HORA: 13:30
LOCAL: Sala de aulas do PPGCEM
TÍTULO:

STUDY OF VACUUM SINTERED FOR Ag-Nb-C COMPOSITE ACTIVATED BY HIGH ENERGY MILLING.

PALAVRAS-CHAVES:

Vacuum sintering, Ag-Nb-C composite, High Energy Milling, NbC, Vickers Microhardness

PÁGINAS: 90
GRANDE ÁREA: Engenharias
ÁREA: Engenharia de Materiais e Metalúrgica
RESUMO:

Due to the enormous relevance of these materials (Ag-Nb-C) and their applications in alloys, although they are normally immiscible with each other, in this work the formation of this composite was studied by mechanical synthesis via high energy milling, with or without post-treatment, and then vacuum’s sintering in solid and in liquid phase of green compacts. Initially, the characterization of the starting powders Ag, Nb, and C (graphite) was performed by X-ray fluorescence, X-ray diffraction (DRX), scanning electron microscopy (SEM) and laser particle size distribution analyzer (LPSDA). The niobium powder was supplied from Escola Politécnica de Lorena (SP),the graphite powder was obtained commercially and the silver obtained from a method described in the literature. For the synthesis process, the high energy milling was used. The composite powders were obtained with the following compositions: powder A = Ag-40 wt% Nb-10 wt% C, powder B = Ag-15 wt% Nb-5 wt% C and powder C = Ag-80 wt%Nb-15wt%C. The milling was performed in 5,10,15, 20 and 30 hours. Subsequently, the powders B and A were heat treated at 400 and 500 ° C, respectively, for 60 min; while powder C was not treated. The powders were then characterized by XRD and compacted at 500 MPa in a 5.0 mm diameter cylindrical die. Three different sintering processes procedures were used. In the first one, from the compacted powder A, isotherm temperatures of 450, 550, 650, and 700°C for 60 min were applied for each milling time of 5, 10, 15 and 20 h; and 1400 ° C for 15 min for the milling time of 10 h. In the second procedure, the compacts of powder B were sintered at 1000 ºC for 30 min with milling of 10 h; and for the third the powder C with milling of 30 h, at 1400 ºC for 15 min. Then, optical microscopy, density measurements by the Archimedes method were made for all sintered samples and XRD and SEM analyzes with dispersive energy spectroscopy (EDS), and Vickers microhardness measurements only for selected samples. In the first procedure, from powder A, a partial densification of the composite occurred, presenting the intermediate sintering stage, for lower temperatures, due to the high energy milling. In the second route, from powder B and C, the NbC was formed, favored by the composition of the mixture, in both cases, besides the effect of the liquid phase sintering temperature. Microhardness values showed variations due to inhomogeneous phase distribution. However, it may be noted that the low values are due to the microhardness of the activated silver, which is in the range of 25 to 70 HV, whereas the nióbium presents values that reach up to 450 HV in certain points. The mean values obtained were for powder A to 450,550 e 650 ºC corresponding to 161 +/- 127, 88,75 +/- 100 and 129,5 +/- 117 HV values.

MEMBROS DA BANCA:
Externo à Instituição - ARIADNE DE SOUZA SILVA - UFRN
Externo ao Programa - 2613355 - FRANCINE ALVES DA COSTA
Externo ao Programa - 2414250 - MEYSAM MASHHADIKARIMI
Presidente - 345842 - UILAME UMBELINO GOMES