Banca de DEFESA: RENAN SÁVIO DE ALMEIDA COELHO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : RENAN SÁVIO DE ALMEIDA COELHO
DATE: 20/03/2023
TIME: 08:00
LOCAL: Plataforma do Google Meeting
TITLE:

Effect of the powder preparation technique and the addition of Nb on the densification and microstructure of WC-Cu-Nb composites sintered with liquid phase.

KEY WORDS:

High energy milling; WC-Cu pseudo alloys; WC-Cu-Nb composites; Sintering.

PAGES: 110
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Metalurgia de Transformação
SPECIALTY: Metalurgia de Pó
SUMMARY:

WC-Cu composites are used as electrical contacts in high power circuit breakers and electrical resistance welding electrodes. This is due to the high thermal and electrical conductivity and excellent workability of copper associated with the high resistance to wear and erosion by electric arc of tungsten carbide. However, the low wettability of liquid copper on tungsten carbide particles and the mutual insolubility of the constituents make it difficult to densify this composite. This work investigates the effect of adding 5 and 10% by mass of Nb to the WC-20%Cu composite and the influence of the powder preparation technique on the microstructure, densification and properties of WC-Cu-Nb composites sintered in liquid phase. The powders were characterized by SEM, EDS, FRX and DRX, while the compact sintered WC-Cu-Nb powders were characterized by SEM, EDS and measurements of density, Brinell hardness and electrical conductivity. The crystallite size of the WC-20%Cu-5%Nb composite powders ground for 5 h in an attritor mill reached 11.0, 11.2 and 26.9 nm for the respective WC, Cu and Nb phases. In contrast, the crystallite size of the same composite powders milled for 10 h in a planetary mill reached only 15.0 and 16.3 nm for the respective WC and Cu phases, but the Nb phase amorphizes or goes into solid solution in Cu. Although the attrition mill produced a greater reduction of crystallites and greater dispersion of the hard WC phase in the soft Cu and Nb phases, contamination by Fe, from the grinding body and chromed steel container, promoted less densification of the powder compacts of the composite. WC-20%Cu-5%Nb, as the compacts of these composite powders ground for 5 h in an attritor mill reached a density of only 71.39 ± 3.38% of the theoretical density, while the compacts of the same composite powders ground for 10 h in a planetary mill, also with chrome steel grinding bodies, reached a density of 81.43 ± 2.7% of the theoretical density. On the contrary, when grinding was carried out in a planetary mill with carbide grinding media, no contamination was detected and the density reached 93.25 ± 3.16%. The addition of Nb contributes to the densification of the WC-Cu composites, as the powder compacts of the WC-20%Cu composite with zero, 5 and 10% by mass of Nb prepared in a planetary mill reached a density, respectively, 77.62 ± 1, 0.65%, 81.43 ±2.70%, 84.34 ± 1.37% of theoretical density when sintered at 1150 °C for 1 hour. Furthermore, the microstructure of the sintered compacts of WC-20%Cu powders with a higher amount of Nb exhibit smaller grain size, confirming their efficiency in inhibiting the grain growth of the sintered composites. Brinell hardness increases with milling time reaching values of 101 HB and decreases with decreasing WC mass. The electrical conductivity increases with the addition by mass of Nb, reaching 2.27% IACS when the amount of 10% by mass of Nb is added to the WC-20%Cu composite.

COMMITTEE MEMBERS:
Presidente - 2613355 - FRANCINE ALVES DA COSTA
Interno - 434906 - AVELINO MANUEL DA SILVA DIAS
Externo ao Programa - 2414250 - MEYSAM MASHHADIKARIMI - UFRNExterno ao Programa - 345842 - UILAME UMBELINO GOMES - UFRNExterno à Instituição - ANGELUS GIUSEPPE PEREIRA DA SILVA - UENF
Externo à Instituição - OSCAR OLIMPIO DE ARAÚJO FILHO - UFPE