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.

Chemical vapor deposition (CVD) diamond films have attracted more attentions due to their excellent mechanical properties. Whereas as-fabricated traditional diamond films in the previous studies don’t have enough adhesion or surface smoothness, which seriously impact their friction and wear performance, and thus limit their applications under extremely harsh conditions. A boron doped, undoped microcrystalline and fine grained composite diamond (BD-UM-FGCD) film is fabricated by a three-step method adopting hot filament CVD (HFCVD) method in the present study, presenting outstanding comprehensive performance, including the good adhesion between the substrate and the underlying boron doped diamond (BDD) layer, the extremely high hardness of the middle undoped microcrystalline diamond (UMCD) layer, as well as the low surface roughness and favorable polished convenience of the surface fine grained diamond (FGD) layer. The friction and wear behavior of this composite film sliding against low-carbon steel and silicon nitride balls are studied on a ball-on-plate rotational friction tester. Besides, its wear rate is further evaluated under a severer condition using an inner-hole polishing apparatus, with low-carbon steel wire as the counterpart. The test results show that the BD-UM-FGCD film performs very small friction coefficient and great friction behavior owing to its high surface smoothness, and meanwhile it also has excellent wear resistance because of the relatively high hardness of the surface FGD film and the extremely high hardness of the middle UMCD film. Moreover, under the industrial conditions for producing low-carbon steel wires, this composite film can sufficiently prolong the working lifetime of the drawing dies and improve their application effects. This research develops a novel composite diamond films owning great comprehensive properties, which have great potentials as protecting coatings on working surfaces of the wear-resistant and anti-frictional components.

The chemical vapor deposition (CVD) method has become a new choice for the fabrication of diamond grinding tools with excellent wear resistance. Different diamond abrasive particles were deposited on the lapping and sandblasting pretreated silicon nitride ceramic substrate by hot filament chemical vapor deposition (HFCVD) method to fabricate CVD diamond abrasive tools. To analyze the influence of pretreatment methods on adhesion strength, the micromorphology, surface roughness, Raman stress, and Rockwell indentation of CVD diamond abrasive tools with different parameters were characterized. Meanwhile, grinding tests on cemented carbide wire drawing dies were carried out, and the grinding performance of different abrasive particles was evaluated. The results show that sandblasting pretreatment can increase the matrix surface roughness, accelerate the growth of diamond abrasive particles and improve the adhesion between the abrasive layer and substrate, and the CVD diamond grinding tool with sandblasting pretreatment substrate and coarse particle has the best dust removal ability and the longest grinding life. The cemented carbide grinding tests of the CVD diamond grinding tool and electroplated diamond grinding tool with the same particle size are processed and compared, it shows that the grinding life of the CVD diamond grinding tool is longer, and the surface roughness value of the workpiece is lower than that of the electroplated diamond grinding tool.