Abstract
Thin boron doped diamond (BDD) film is deposited from trimethyl borate/acetone/hydrogen mixture on Co-cemented tungsten carbide (WC-Co) micro drills by using the hot filament chemical vapor deposition (HFCVD) technique. The boron peak on Raman spectrum confirms the boron incorporation in diamond film. This film is used as an interlayer for subsequent CVD of micro-crystalline diamond (MCD) film. The Rockwell indentation test shows that boron doping could effectively improve the adhesive strength on substrate of as deposited thin diamond films. Dry drilling of graphite is chosen to check the multilayer (BDD + MCD) film performance. For the sake of comparison, machining tests are also carried out under identical conditions using BDD and MCD coated micro drills with no interlayer. The wear mechanism of the tools has been identified and correlated with the criterion used to evaluate the tool life. The results show that the multilayer (BDD + MCD) coated micro drill exhibits the longest tool life. Therefore, thin BDD interlayer is proved to be a new viable alternative and a suitable option for adherent diamond coatings on micro cutting tools.
Highlights
Graphite is the most widely used material for electrical discharge machining (EDM) electrodes due to its low electrode abrasion, light weight, low cost and especially excellent high temperature endurance in the spark arc when compared with cooper [1,2]
The effectiveness of boron doped diamond (BDD) interlayer on cutting performance of diamond coated micro drills is investigated in dry drilling of high quality EDM graphite
The broad peaks around 1220 cm−1 and 500 cm−1, which are the feature of boron incorporation in the diamond lattice, are visible in Raman spectrum of BDD coating and BDD interlayer on micro drills
Summary
Graphite is the most widely used material for electrical discharge machining (EDM) electrodes due to its low electrode abrasion, light weight, low cost and especially excellent high temperature endurance in the spark arc when compared with cooper [1,2]. Tools suffer severe wear on their cutting edges due to abrasive properties of graphite powders formed during graphite machining To enhance their cutting performance in the machining of high quality EDM graphite, cutting tools are proposed to be coated on wear-resistant diamond thin films using the hot filament chemical vapor deposition (HFCVD) technique as it is convenient to directly deposit diamond thin films on tools with complex geometries by this method [3,4,5,6]. The major difficulty in depositing diamond on WC-Co tools arises from the binder Co, which induces graphitization during HFCVD procedure This would result in poor adhesive strength between substrates and diamond coating and further up restrict the application of diamond coated cutting tools. An interlayer is introduced to deposit between the substrate and diamond film to further enhance diamond coating adhesion and prolong tool life. Films on WC-Co micro drills that have been pre-coated with BDD interlayer, with an emphasis on the cutting performance enhancement of BDD + MCD coated micro drills compared with MCD or BDD coated micro drills in graphite machining
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