Xiang Feng Li

Adhesion improvement of CVD diamond film by introducing an electro-deposited interlayer

Abstract It is proposed to use Ni–Mo alloy produced by electro-deposition as a transient layer for the adhesion improvement of chemical vapor deposition (CVD) diamond film on Cu substrate. A layer of Ni–Mo alloy is firstly electro-deposited on Cu, and then diamond film is deposited by microwave plasma CVD. Metallurgical combination was found to form in both the interface of Ni–Mo alloy/Cu and the interface of diamond film/Ni–Mo alloy. An adherent diamond film was successfully obtained on Cu because of the combined actions of the interface compounds and the reduction in the thermal stress. The process proposed in this study will provide a new approach for diamond film deposition on cemented carbides, which are cutting tool materials in common use.

Study on EDM Polishing of CVD Diamond Films

Chemical vapor deposition (CVD) diamond is known for its superior characteristics such as hardness, toughness and wear resistance. However, due to these factors, machining CVD diamond is a difficult material removal process. A new technique to polish CVD diamond film efficiently is reported in the present paper. In the CVD deposition process, boron was doped into diamond to fabricate high-quality semi-conductive film, which make it possible to machine diamond film by electro discharged machining (EDM) method. The relationship between EDM parameter and removal processing was investigated in details. The machined surface of boron doped (B-doped) diamond films was studied by Scanning Electron Microscope (SEM) and Raman Scattering Spectroscopy (Raman). The experimental results show that EDM polishing is a highspeed material removal and low cost method for CVD diamond polishing. When the discharge current and pulse-on time increase in a certain range, the cutting-off speed and roughness will increase correspondingly. The roughness of EDM polished CVD diamond film surface is Ra<0.5μm when the discharge current is at 4A and pulse-on time is at 200μs.

Preparation of Nanocrystalline Diamond Films on Molybdenum Substrate by Double Bias Method

The synthesis of nanocrystalline diamond film on polycrystalline molybdenum substrates was carried out by using of self-made hot filament chemical vapor deposited (HFCVD) system. Positive bias voltage on the grid electrode on top of hot filaments and negative bias voltage on the substrate were applied. High purity and extremely smooth nanocrystalline diamond films were successfully prepared by using the double bias method. Raman, SEM, XRD and AFM results show that the diamond films obtained have grain sizes less than 20nm, nucleation density higher than 1011cm-1. The mechanism of double bias is also discussed in this paper. The positive grid bias increases the active, decomposition and ionization of hydrogen and methane molecules, while negative substrate bias helps positive carbon-containing ions bombard the substrate that leads to the high nucleation density of the diamond film.

Smoothing of Thick Diamond Film Prepared by Electron-Assisted CVD

This paper focused on the smoothing of thick diamond film prepared by electron-assisted chemical vapor deposition (EACVD), whose equipment was developed by the authors. CO2 laser and YAG laser were used to scan the film surface. It is shown that CO2 laser is not suitable to the surface smoothing, while YAG laser is effective to remove the salience on the film surface, though thermal damage occurs in the surface to some extent. A final mechanical lapping was introduced to remove the damaged layer occurred in the laser smoothing. The results showed that a low roughness Ra 0.1μm could be obtained with a high efficiency. Introduction Low processing efficiency is an important problem left in the application of CVD thick diamond film in engineering, although its super performance enables it to have so wide range of application not only in mechanical engineering but also in electronical and aeronautical ones. Generally, cutting-off, grinding, lapping, polishing and brazing are needed when the thick film is applied to some cutting tools or mechanical parts, where it will take much time to smooth the film because of its super hardness. As a result, a high processing cost plus the high cost of the film itself become restriction to its popular application. Much attention has been paid to the smoothing of CVD diamond film, and some new methods were applied to the smoothing, such as ion beam irradiation, hot-iron-metal polishing, etc [1-3]. Attention was also paid to precision micro-machining for the film [4]. In this paper, experiments were conducted on smoothing of thick diamond film prepared by EACVD [5], and the effects of laser scanning and mechanical lapping condition on the surface roughness and surface quality were investigated [6]. For the thick film used, it had an initial diameter of about 100 mm and a thickness of 0.6 mm. It was cut into small circle pieces by using of YAG laser for smoothing experiments. A special set-up was designed to adjust the incident angle of laser beam when scanning the film surface. Holing experiments were firstly made as pretest to investigate the effect of laser power on the diamond removal. The surface roughness was measured and compared under different conditions, and the smoothed surface was observed by using of SEM. Raman spectrum analysis was conducted after laser smoothing and mechanical lapping. Laser Processing CO2 Laser Processing. Laser is a typical kind of the beams that have high-density power, and it has been applied widely in material removing, not only for metal materials but also for non-metal ones. CO2 laser is powerful and able to show high efficiency in cutting-off of thick steel plates, and it is also effective to process difficult-to-machine materials such as ceramics. For the reason, in this study trials were made to use CO2 laser as a pre-smoothing method for the initial rough surface of thick diamond films as shown in Fig.1a. Experiments were made in Engineering Center of Laser & Advanced Manufacturing, Jiangsu University. The laser power, its spot diameter and scanning speed were changed in the experiments, and the incident angle of laser beam , as shown in Fig.1b, was adjusted by using of the specially Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 507-511 doi:10.4028/www.scientific.net/KEM.259-260.507

Boron-Doped Nanocrystalline Diamond Films Deposited By Using DC Arc Plasma Jet CVD

Boron-doped micro-nanocrystalline diamond coating may be successfully prepared on Mo substrate with DC arc plasmas jet deposition device. Along with the increase of doped-boron concentration in the film, two-point resistance measurement indicates that film resistance presents exponential decrease; Raman spectrum test shows that, the characteristic peak value of diamond 1332cm-1 in the spectrum moves toward low frequency, the semi-height width of diamond peak, peak D and peak G, etc. in the spectrum is expanded, and the component of non-diamond bonds such as sp2, etc. in the film is increased; SEM and AFM observation shows that, increasing the doped-boron concentration could further subdivide the crystal grains in the film, and is beneficial for the growth of nano- or ultra-nano-crystalline diamond film; film annealing test shows that, micro-nanocrystalline diamond film with higher doped-boron concentration has better thermal stability than the micro-nanocrystalline diamond film without doped boron.

Thermal Shock Behaviors of Laser Cladding NiCoCrAlY Coatings Strengthened by Nanometric SiC Particles

Three NiCoCrAlY coatings strengthened by different contents of nano-SiCp (nanometric SiC particles)were prepared on Ni-based superalloy substrates using crosscurrent CO2 laser, and the thermal shock test of these coatings was conducted by cycling between 1050°C and room temperature (10-15°C). The spalled area in the oxide scale of coatings after 10 thermal shock cycles and the thermal shock cracks in the cross-section of coatings after 100 thermal shock cycles were investigated using SEM, OM, and other means. The results show that the thermal shock resistances of NiCoCrAlY coatings are improved after adding nano-SiCp. Among nano-SiCp-added coatings, the coating added with 1.0 wt% nano-SiCp performs best. After 10 thermal shock cycles, there is a slight spallation whose area is only 2.65% in the oxide scale of the coating; after 100 thermal shock cycles, no internal crack is observed in the cross-section, and the amount and size of propagating cracks are slight.

Simulation Research on Elastic Constant and Natural Frequency of NCD Coated AFM Probes

In this work, the elastic constant and natural frequency of NCD and non-NCD coated AFM probes were simulated using ANSYS. The results indicated that after depositing 1～2μm thick NCD films on the silicon probes, the elastic constant and natural frequency were both increased, yet within the prescribed limit: when the cantilevers had the same total thicknesses (3μm, 3.5μm and 4μm), the elastic constant and the natural frequency of the NCD coated probes were increased by 96%～107% and 28%～30% respectively, compared with the silicon probes.

Simulation Study of the Temperature Field for Squashed Presetting Laser Cladding Based on ANSYS

In the process of modeling the squashed piece of powders for the simulation of the temperature field of laser cladding, the metallurgical model and the pore model were proposed separately. The effects of the organizational form, the contact resistance and the thickness of the squashed piece of powders on the temperature were considered. Different values of physical parameters of the squashed piece of powders were converted, different contact resistances were calculated and the laser absorptivity for different process parameters of laser cladding was determined. The temperature curves of six typical nodes and the temperature gradient of two nodes in the molten pool of the substrate were discussed from different aspects.

Fatigue Life Simulation on Forestay Bar of Aircraft Landing Gear

Firstly, taking the stability of the forestay bar as the restraint, the section area of the forestay bar was optimized from 1800 mm2 to 1178 mm2, with reduced weight of 16.1%. Secondly, the equivalent load of the forestay bar was obtained by using dynamics simulation software. Finally, the stress field and the fatigue life of the forestay bar were simulated. The results show that stress of the forestay bar with 929MPa can meet the requirement for its material strength, and fatigue life of 51200 times also satisfies the request of the nose landing gear. That is, material property of the forestay bar is utilized more than before, and its weight decreased successfully.

Recognition for Spindle Speeds of Drill Press Based on Sound Signals Produced from Drilling

Effects of running state and spindle speeds on the sound signals produced from a drill press are investigated. And the obtained sound signals by using of a sound level meter are analyzed in both time domain and frequency domain. It is evident that there is more high frequency energy for drilling sound signals with load than without load. And spindle speeds still affect their energy distribution of drilling sound signals. Using wavelet decomposition and wavelet packet decomposition, drilling sound signals are decomposed into a number of frequency bands. And energy percentages of the divided frequency bands are extracted to be the effective characteristics to recognize spindle speeds. Meanwhile, training error of different BP networks is compared to obtain the effective network for recognition spindle speeds. By using of the obtained network structure named 16-30-5, the study rate for training samples and the recognize rate for testing samples are all above 95%.