Silicon carbide (SiC) is a promising material for fabricating wire compacting dies due to its advantages of light weight and even high wear resistance over the tungsten carbide, which currently is the most popular material used to produce compacting dies. In present study, a layer of CVD diamond film is deposited on the interior-hole surface of compacting dies using the hot filament chemical vapor deposition (HFCVD) method, following by a surface polish process, aiming at further elongating the lifetime of compacting dies and improving the surface quality of produced wires. The characterization of both as-deposited and polished CVD diamond films is employed by scanning electron microscopy (SEM), surface profiler, Raman spectroscopy and X-ray diffraction (XRD) spectroscopy. Furthermore, the performance of as-fabricated CVD diamond coated compacting dies is examined in the real production process. The results exhibit that the as-deposited CVD diamond films are homogeneous and their surface finish is significantly smoothened after the surface polish process. As compared with the conventional compacting dies, the working lifetime of the diamond coated SiC compacting dies can be increased by a factor of above 15 and in the course of processing, copper stranded wires with high surface quality and uniform sectional area can be obtained.

In the present investigation, both micro-crystalline and nanocrystalline diamond (MCD and NCD) films are fabricated, which are characterized by FESEM (Field Emission Scanning Electron Microscopy), surface profilemeter, Raman spectroscopy and Rockwell hardness tester. Moreover, under the dry environment, the frictional behavior of both the films sliding against commonly-used materials in the metal drawing industry is studied on a ball-on-plate rotational frictional tester, including the stainless steel, low-carbon steel, high-carbon steel and copper, demonstrating that the frictional coefficients between NCD films and all these materials are relatively smaller. Furthermore, the wear rates of both the films, which are hardly measured in the ball-on-plate friction tests, are evaluated using a home-made inner-hole line drawing apparatus, with both the diamond films deposited on the inner-hole surfaces and the low-carbon steel wires as the counterparts. Inversely, the NCD films present higher wear rates than the MCD ones, which can be attributed to the deteriorative film purity and adhesion.

In the present investigation, titanium (Ti), silicon carbide (SiC), silicon (Si) and tantalum (Ta) samples with the same geometry are selected as substrates to deposite HFCVD boron-doped diamond films with the same deposition parameters, using trimethyl borate as the dopant. FESEM, EDS, Raman spectroscopy and Rockwell hardness tester are used to characterize as-deposited boron-doped diamond (BDD) films. The FESEM micrographs exhibit that the film deposited on Si substrate presents the best uniformity and that on Ti substrate has smallest grain size and film thickness, with titanium element detected in the EDS spectra. Moreover, it’s speculated by indentation test that the adhesive strength between the BDD films and different substrates can be order as SiC>Ta>Ti for the different thermal expansion coefficient gaps between the substrate and diamond, and the hardness of the BDD coated samples measured using Rockwell hardness tester can also be order as SiC>Ta>Ti due to the different hardness of substrate materials. Finally, similar and representative characterization for BDD films is obtained from the Raman spectra for all the BDD films on different substrates.

Carbon fiber reinforced plastics (CFRP), which are widely used in the aerospace and some other new-tech industries, are considered very difficult to machine due to the material anisotropic and inhomogeneous features. Chemical vapor deposition (CVD) diamond films are suitable as protective coatings on cutting tools for machining advanced composite materials, owing to their extremely high hardness, favorable wear resistance, low friction coefficient and high thermal conductivity. Among different types of diamond films, the fine grained diamond (FGD) film can provide much more favorable environment for machining CFRP due to the small grain size, low surface roughness and the retentivity for the sharpness of the cutting edge. In the present study, aiming at drilling CFRP, FGD films of different thicknesses are deposited on Φ3 mm drills by controlling the growth time, adopting the common-used hot filament CVD (HFCVD) technology. It can be directly proved by deposition experiments that overlong growth time can induce spontaneous film delamination and removal before the cooling stage, probably as a result of the excessive residual stress concentrated on the complicated surfaces. As demonstrated by the cutting tests, with increasing the growth time, the main failure mode of the FGD coated drill changes from film delamination to flank wear/tipping to film delamination, and the maximum tool life exists when the growth time is moderate, because the flimsy film cannot provide sufficient protective effects on the film-substrate interface and even hasn’t totally cover the substrate, while there’s relatively higher residual stress in the film that is too thick, and such the residual stress can significantly deteriorate the film-substrate adhesion. Moreover, during the life cycle of each FGD film, relatively shorter growth time often means the slightly better hole quality, attributed to the retentivity of the initial shape of the uncoated drill that is optimal designed for machining CFRP, especially the weaker passivation of the cutting edge.

In the present study, high-quality chemical vapor deposition (CVD) micro-crystalline diamond (MCD) film was successfully deposited on the surface of the Φ0.5 mm×120 mm tungsten wire using a special designed graphitic jig for supporting the substrate and a two-step deposition procedure for guaranteeing the uniformity of as-deposited diamond film. It is proved that as-deposited film indeed presented much more uniform thickness than that obtained using a conventional jig described in the previous literature, and a very thick WC interlayer spontaneously formed between the substrate and the diamond film, which together with as-deposited MCD film have significant effects on mechanical properties of the wire. Generally speaking, the coated wire remains extremely high surface hardness of the MCD film and considerable toughness of the substrate, along with favorable film-substrate adhesion. It is recognized that these the coated tungsten wires have broad application prospects, but the technologies for depositing diamond films that are thick enough on even longer and thinner wires still need further investigation.