Banca de QUALIFICAÇÃO: RENAN SÁVIO DE ALMEIDA COELHO

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : RENAN SÁVIO DE ALMEIDA COELHO
DATE: 31/08/2021
TIME: 14:00
LOCAL: Sala de vídeo conferência 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: 73
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 switches and electrical resistance welding electrodes. This is due to the high thermal and electrical conductivity and excellent workability of copper associated with the high wear resistance and electrical arc erosion of tungsten carbide. However, the low wettability of liquid copper on tungsten carbide and the mutual insolubility of the constituents hinder the densification of these composites. This work investigates the effect of adding 5 and 10% Nb by mass to WC-20%Cu composite and the influence of the powder preparation technique on the microstructure, densification and properties of sintered WC-Cu-Nb composites. The powders were characterized by SEM, EDS, FRX and DRX, while the sintered WC-Cu-Nb composite powder compacts were characterized by SEM, EDS and measurements of density, Vickers microhardness and electrical conductivity. The crystallite size of the WC-20%Cu-5%Nb composite powders milled for 5 h in an attritor mill reached 11.0, 11.2 and 26.9 nm for the respective WC, Cu and Nb phases. Differently, 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 amorphized or entered a solid solution in Cu. Although the attritor mill produces a greater reduction in crystallites and a greater dispersion of the WC hard phase in the soft Cu and Nb phases, the Fe contamination, coming from the grinding media and container, promotes lower densification of the WC-20%Cu-5%Nb composite powder compacts, as compacts of these composite powders milled for 5 h in an attritor mill reached a density of only 71.39% of the theoretical density, while compacts of the same composite powders milled for 10 h in a planetary mill reached a density of 81.43% of theoretical density. The addition of Nb contributes to the densification of WC-Cu composites, as the compacts of WC-20%Cu composite powders with zero, 5 and 10% by mass of Nb prepared in a planetary mill reached a density, respectively, of 77.62%, 81.43%, 84.34% of theoretical density when sintered at 1150 oC for 1 hour. Furthermore, the microstructure of the sintered compacts of WC-20%Cu powders with higher amounts of Nb exhibit smaller grain size, confirming its efficiency in inhibiting the growth of the grains of the sintered composites.

BANKING MEMBERS:
Presidente - 2613355 - FRANCINE ALVES DA COSTA
Interno - 434906 - AVELINO MANUEL DA SILVA DIAS
Interno - 2414250 - MEYSAM MASHHADIKARIMI
Externo ao Programa - 345842 - UILAME UMBELINO GOMES