Novel conversion annealing pretreatment for improved deposition of diamond coatings onto WC-Co cemented carbide

The present investigation deals with the definition of a new eco-friendly alternative to pretreat Co-cemented tungsten carbide (WC-Co) substrates before diamond deposition by hot filament chemical vapor deposition (HFCVD). In particular, WC-5.8 wt %Co substrates were submitted to a thermal treatment by a continuous wave-high power diode laser to reduce surface Co concentration and promote the reconstruction of the WC grains. Laser pretreatments were performed both in N(2) and Ar atmosphere to prevent substrate oxidation. Diamond coatings were deposited onto the laser pretreated substrates by HFCVD. For comparative purpose, diamond coatings were also deposited on WC-5.8 wt %Co substrates chemically etched by the well-known two-step pretreatment employing Murakami's reagent and Caro's acid. Surface morphology, microstructure, and chemical composition of the WC-5.8 wt %Co substrates after the different pretreatments and the deposition of diamond coatings were assessed by surface profiler, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction analyses. Wear performance of the diamond coatings was checked by dry sliding linear reciprocating tribological tests. The worn volume of the diamond coatings deposited on the laser pretreated substrates was always found lower than the one measured on the chemically etched substrates, with the N(2) atmosphere being particularly promising.

Diamond coated cutting tools are applied for machining difficult-to-machine materials of titanium alloys. However, the temperature field uniformity needs to be further improved for the mass production of diamond coated tools using the hot filament chemical vapor deposition (HFCVD) method. In this paper, the tools temperature distribution is simulated by the finite volume method (FVM) during the deposition of diamond coatings. An optimization method of deposition setting with fine filaments in dense arrangement (FFDA) is proposed, and the temperature distributions of the tools under the coarse filament in sparse arrangement (CFSA) and FFDA are simulated to systematically elucidate the effects of fine filament densification. Subsequently, the different hot filament arrangements are adopted to mass production experiment for deposition of micro/nano composite diamond (MCD/NCD) coatings on WC-6%Co cutting tools. In addition, the cutting experiments on titanium alloys are conducted using diamond coated tools, and the cutting performance of tools at different locations is evaluated. The results indicate that the FFDA method can improve the temperature field uniformity of mass-produced diamond coated cutting tools, and the cutting tools have better consistency in surface morphology, thickness, chemical composition, surface roughness and cutting performance.

Effect of doping level on residual stress, coating-substrate adhesion and wear resistance of boron-doped diamond coated tools

Among the unique opportunities and developments that are currently being triggered by the fourth industrial revolution, developments in cutting tools have been following the trend of an ever more holistic control of manufacturing processes. Sustainable manufacturing is at the forefront of tools development, encompassing environmental, economic, and technological goals. The integrated use of sensors, data processing, and smart algorithms for fast optimization or real time adjustment of cutting processes can lead to a significant impact on productivity and energy uptake, as well as less usage of cutting fluids. Diamond is the material of choice for machining of non-ferrous alloys, composites, and ultrahard materials. While the extreme hardness, thermal conductivity, and wear resistance of CVD diamond coatings are well-known, these also exhibit highly auspicious sensing properties through doping with boron and other elements. The present study focuses on the thermal response of boron-doped diamond (BDD) coatings. BDD coatings have been shown to have a negative temperature coefficient (NTC). Several approaches have been adopted for monitoring cutting temperature, including thin film thermocouples and infrared thermography. Although these are good solutions, they can be costly and become impractical for certain finishing cutting operations, tool geometries such as rotary tools, as well as during material removal in intricate spaces. In the scope of this study, diamond/WC-Co substrates were coated with BDD by hot filament chemical vapor deposition (HFCVD). Scanning electron microscopy, Raman spectroscopy, and the van der Pauw method were used for morphological, structural, and electrical characterization, respectively. The thermal response of the thin diamond thermistors was characterized in the temperature interval of 20–400 °C. Compared to state-of-the-art temperature monitoring solutions, this is a one-step approach that improves the wear properties and heat dissipation of carbide tools while providing real-time and in-situ temperature monitoring.

Improvement in the universality of high-performance CVD diamond coatings on different WC-Co substrates by introducing multilayered diamond/β-SiC composite

Diamond coatings were prepared on alumina by hot filament chemical vapor deposition, which constituted an insulator used in a laser pump. The composition and morphologies of the diamond coatings were characterized by Raman spectra and scanning electron microscope. The effects of the pressure of the deposition chamber and the distance from the filament to the base on the composition and structure of the deposited diamond coatings were studied.

Tribological and mechanical properties of HFCVD diamond-coated WC-Co substrates with different Cr interlayers

abstractBoronizing treatment was done to form a boride surface layer well bonded with cemented carbide substrate. Multilayer microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) coatings were prepared on the boronizing cemented carbide substrate by hot filament chemical vapor deposition (HFCVD) method. The surface and the cross section micrograph, coating component, hardness and adhesion of the as-deposited diamond coatings were observed with a SEM, Raman spectroscopy, nano-indenter and a Rockwell hardness tester accordingly. The results show that the MCD coating consists of well-faceted grains and the hardness of the MCD coating is about 85GPa. The NCD coating has morphological features with grain sizes of several tens of nanometer. The hardness of the NCD coating is about 52GPa. The boron doping of cemented carbide substrate can improve the fracture strength of the diamond film to some extent, and the adhesion of multilayer NCD/MCD coating is better than that of monolayer MCD and monolayer NCD coating.

Diamond coatings are deposited on the end surfaces of mechanical seal rings by the hot filament chemical vapor deposition (HFCVD) method. To improve the homogeneity of batch preparation of HFCVD diamond-coated seal rings, the temperature distributions on the end surfaces of seal rings are simulated and optimized using the finite volume method (FVM). The influence mechanism of various setup parameters on coating deposition is demonstrated systematically with the orthogonal experimental method, including the filament diameter d, the filament temperature [Formula: see text], the separation between two adjacent filaments D and the filament height H. The optimal HFCVD setting parameters for batch preparation of diamond-coated seal rings are proposed based on the simulation results of orthogonal experiments. Afterwards, mass deposition experiments of seal rings are conducted using the optimal setting parameters, and the diamond coatings deposited on the end surfaces of seal rings are characterized. Furthermore, mechanical seal operation bench tests are carried out to evaluate the abrasion resistance of diamond-coated seal rings. The results indicate that the optimized setting parameters can produce a homogeneous temperature field, and diamond coatings with uniform thickness and excellent wear resistance can be obtained in the batch preparation of diamond-coated seal rings.

The adhesion of wear-resistant diamond coating deposited on titanium was weakened by the porous titanium carbide interlayer, which was formed before film growth. In order to enhance substrate-coating adherence, a new pretreatment method was presented: Ti substrates were carbonized by hot filament chemical vapor deposition system, and then the carbonized substrates were ultrasonically vibrated using diamond micro-powder suspension. Diamond coatings were deposited by hot filament chemical vapor deposition as well. The effect of carbonization time on adhesion was investigated. The carbonized substrates and the interface between diamond coatings and substrates were characterized. The results showed that as the carbonization time increases, porous structures and cracks appear and increase on the surface of the substrate. The carbonized substrates possess high surface energy and thus the nucleation is promoted. After deposition, a dense and thin titanium carbide was observed. Ultrasonic after carbonization pretreatment can significantly enhance the adhesion of Ti-based diamond coatings by promoting nucleation and suppressing the formation of porous titanium carbide.

Dry turning of alumina/aluminum composites with CVD diamond coated Co-cemented tungsten carbide tools

Effect of substrate grain size and surface treatments on the cutting properties of diamond coated Co-cemented tungsten carbide tools

Fluidized bed micro-machining and HFCVD of diamond films onto Co-cemented tungsten carbide (WC-Co) hardmetal slabs

Coating thickness and interlayer effects on CVD-diamond film adhesion to cobalt-cemented tungsten carbides

Performance and characterisation of CVD diamond coated, sintered diamond and WC–Co cutting tools for dental and micromachining applications