abstract
Drilling of pre-sintered cemented carbide parts is a challenging task due to the high hardness and abrasive nature of the WC grains. This operation is commonly done using uncoated cemented carbide drill bits but the tool life is very limited requiring tool re-sharpening after a few holes. A solution for the improvement of the tool performance is here exploited by the use of nanocrystalline diamond (NCD) films as high abrasion resistant coatings. These coatings were grown in a hot filament chemical vapor deposition (HFCVD) reactor. Filament temperatures in the range of 1940-1980 degrees C were crucial to obtain highly adherent and very uniform coatings at the cutting edge and on the surfaces of the flutes. The performance of the coated tools was evaluated in through-hole drilling of a pre-sintered cemented carbide showing outstanding cutting efficiency when compared to that of an uncoated tool: maximal 940 mm/min infeed rates (app. 1 s to drill 17 mm) instead of 20 mm/min for the latter; absence of tool wear in contrast to a flank wear of about 50 pm in the uncoated tool after only 4 holes; hole edge integrity even at the highest infeed rates while grain decohesion at the hole edge takes place when using bare drill bits. (C) 2011 Elsevier Ltd. All rights reserved.
keywords
CHEMICAL-VAPOR-DEPOSITION; COATED CUTTING TOOLS; TUNGSTEN CARBIDE; INTRINSIC STRESS; GREEN BODIES; FILMS; ADHESION
subject category
Materials Science; Metallurgy & Metallurgical Engineering
authors
Almeida, FA; Carrapichano, JM; Fernandes, AJS; Sacramento, J; Silva, RF; Oliveira, FJ
our authors
Filipe José Alves de Oliveira
Principal Researcher
Flávia Aparecida de Almeida
Post-doc Fellowship
Rui Ramos Ferreira e Silva
Associate Professoracknowledgements
F.A. Almeida acknowledges FCT grant SFRH/BPD/34869/2007. The financial funding from the FCT Project MULTIDIACOAT PTDC/EME-TME/100689/2008 is also gratefully acknowledged.