Narrow Results

The temperature field distribution uniformity has a crucial influence on growing high-quality diamond grains by hot-filament chemical vapor deposition (HFCVD). In this paper, we explored the effect of the temperature of the tungsten wire on the temperature field distribution on the surface of the polycrystalline diamond compact (PDC) substrate using the finite element method and found that, with the temperature of tungsten wire being 2200^∘C, it is suitable for the growth of diamond grains and the temperature distribution is more uniform. Meanwhile, the HFCVD method has been used to probe the effect of the parameters of the hot wire power on the diamond grains filling hole and the quality of the diamond film on the PDC surface, analyzed by various characterizations including SEM, XRD, Image J, and Raman. It turned out that both the size of the diamond grains and the acceleration of the deposition increase, as the hot wire power is increased. The size of the diamond grains decreases when the hot wire power is increased to 4.00kW, while the uniform and cauliflower-like nanodiamond films are formed. However, the hot wire power continued to increase and the deposition focused on the growing graphite phase rather than the diamond phase, resulting in a decrease in the quality and properties of the diamond film. The study was able to achieve good tenacity and wearability of the PDC for applications in oil drilling and ultra-hard coating tools.

We study the epitaxial growth mechanism of diamond films using various hetero-materials as substrates in a hot-filament chemical vapor deposition (HFCVD) chamber. The same parameters were maintained in the nucleation and growth processes of diamond films on these substrates. The experimental results showed that the dominant orientation of diamond crystals has a relation with that of substrates identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The preference of diamond films on non-diamond substrates is explained as heteroepitaxial growth. We think that the initial nucleation process is the key to the heteroepitaxial growth of diamond film.

The surface temperature field model of hot filament chemical vapor deposition (HF CVD) diamond films on WC–Co alloys was constructed and calculated by taking into account the influences of both thermal source properties and physical properties of substrates. Under the certain conditions of some parameters, the effects of the influence factors such as the maximum specific heat flux (q_m), the heat conductivity coefficient (λ) of the substrate and the substrate height (h) on the surface temperature field were exhibited quickly and clearly by the computer modeling. The theoretical calculating data are close to the experimental results. It is found that the influences of the thermal source parameter, the substrate height, and the heat conductivity coefficient of the substrate materials on the surface temperature field of diamond films on WC–Co alloys are almost equally important.

The finite element method (FEM) is employed to analyze the residual stress distribution of bi-layer (a-SiC $+$ diamond) film system, and the adhesion enhancement mechanism of a-SiC interlayer is further investigated. The influence of a-SiC interlayer on the surface topography of WC-Co substrate is taken into consideration by adopting a 3D surface topography model agreeing with the Atomic Force Microscope (AFM) characterization of a-SiC interlayer. For the sake of comparison, the stress distribution of a diamond film with no interlayer is also simulated. The simulation analysis reveals that the residual stress distribution is much more homogeneous after employing the a-SiC interlayer, which is supposed to be of great importance to the adhesion enhancement of diamond films. Afterwards, the diamond films with and without a-SiC interlayer are fabricated on WC-Co substrates. Raman mapping is carried out to measure the real residual stress distribution of as-fabricated a-SiC diamond films, which is in accordance with the simulation results. Moreover, the a-SiC interlayered diamond film exhibits better adhesion than the diamond film with no interlayer in adhesion evaluation, which can be ascribed to the more homogeneous residual stress distribution and better interfacial bonding after introducing the a-SiC interlayer.

In this study, the effect of diamond interlayer on the tribological properties of titanium aluminum nitride (TiAlN) film sliding against medium carbon steel is investigated in dry rotary friction tests, by evaluating the coefficients of friction (COFs), wear rates, worn surfaces and element transitions of the contacted surfaces in the cemented carbide (WC-Co)-steel, TiAlN-steel, microcrystalline diamond (MCD)-steel, TiAlN/MCD-steel, micro- and nano-crystalline diamond (MNCD)-steel and TiAlN/MNCD-steel contacting pairs. It is found that compared with the TiAlN monolayer, the TiAlN/MCD bilayer film shows 57% higher COF, while the COF of TiAlN/MNCD multilayer inversely drops as much as 54%, due to the distinguished surface diamond grain morphologies of the MCD and MNCD interlayers as well as the copied effect of the TiAlN layer with relatively small thickness. Meanwhile, the diamond interlayer can provide robust load support for the top TiAlN layer, induce the wear mechanism transform from the abrasive wear to adhesive wear, and result in the mild wear of TiAlN/MCD and TiAlN/MNCD multilayers compared to the TiAlN monolayer. Moreover, the softer TiAlN top layer on MCD and MNCD interlayers can effectively improve the storage capacity of element oxygen and worn steel ball debris as well as accelerating the surface chemical reactions to form a smoother continuous ionic metal oxides tribofilm in the contacted zones due to its good self-lubricating property. Among all the hard coatings discussed when sliding against medium carbon steel, the TiAlN/MNCD coating shows the lowest COF and mild wear, due to the robust load support capacity of the beneath MNCD layer as well as the good self-lubricated and tribofilm formation capacity of the top TiAlN layer, which shows broad application potential in carbon steel machining.

This study is focused on the tribological properties of micro- and nano-crystalline diamond (MCD and NCD), non-hydrogenated and hydrogenated diamond-like carbon (DLC and DLC-H) and nitrogen-based (CrN, TiN and TiAlN) coatings sliding against the super alloy Inconel 718, in terms of the maximal and average coefficients of frictions (COFs), the worn morphologies and the specific wear rates, by the rotating ball-on-plate configuration under dry condition. The results show that the nitrogen-based films show comparable COFs and wear rates with the WC–Co substrates. The DLC and DLC-H show lower COFs compared with the nitrogen-based films. Furthermore, their wear resistance is limited due to their low thickness compared with MCD and NCD, which have the same elemental composition. The DLC-H coating exhibits much lower wear rate compared with the DLC coating, which may be derived from the passivation of dangling bonds by the linking of H to C atoms. The MCD and NCD films show the lowest average COFs and mild wear after tribotests, due to their high hardness and low adhesive strength between pure diamond and the super alloy.

Among all the tested films, the NCD film-based tribopair presents the lowest maximal and average COFs, tiny wear debris particles, mild wear of ball and plate without scratching grooves, indicating that the NCD film may be suitable to be deposited on cutting tools for super alloy machining.

Zinc oxide (ZnO) nanorods (NRs) have been synthesized as a template to fabricate TiO₂ nanotubes (TiNTs) on hemispherical diamond film by liquid-phase deposition (LPD) method. The process concerning the formation of TiNTs was analyzed. Based on the results of XRD and Raman spectroscopy, it is demonstrated that TiNTs was successfully obtained after removing ZnO NRs by chemical etching at room temperature. The TiNTs on hemispherical diamond film show higher performance photocatalysis, examined by the degradation of the reactive yellow 15 (RY15) solution. The corresponding mechanism is discussed.

Dry cutting can eliminate a series of negative effects of coolant. Based on tribology principle of coated tool, diamond film coated tool is used to cut the same workpiece under the conditions of dry-cutting and coolant. The tool's cutting properties and wear mechanism are studied by tests. Results imply that this coated tool will be applied more widely day by day in the dry-cutting.