Nanocrystalline CVD diamond coatings for drilling of WC-Co parts

• Published in: International journal of refractory metals & hard materials Vol. 29; no. 5; pp. 618 - 622
• Main Authors: Almeida, F.A., Carrapichano, J.M., Fernandes, A.J.S., Sacramento, J., Silva, R.F., Oliveira, F.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2011
• Subjects: Cemented carbide; Cemented carbides; Chemical vapor deposition; Diamond tools; Drill bits; Drilling; Filaments; Machining; Nanocrystalline diamond; Tool wear; Drilling; Cemented carbide; Nanocrystalline diamond; Machining; Tool wear
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2011.04.008

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
°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
μm 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.
► Good quality and adherent NCD diamond coated drills were produced by HFCVD method. ► High efficiency in drilling WC-Co pre-sintered parts up to 940 mm/min infeed rates. ► No tool wear and hole edge integrity even at the highest infeed rate.