Fang Hong Sun

Simulation of Substrate Temperature Distribution in Diamond Films Growth on Cemented Carbide Inserts by Hot Filament CVD

Three-dimensional finite element simulations were used to investigate the influences of various hot filaments and other deposition parameters on the temperature field of substrates which affect significantly the growth and quality of diamond films by hot filament chemical vapor deposition (HFCVD) and based on the simulation results, the optimum position for diamond deposition was found. In the experiment, six cemented tungsten carbide inserts were used as substrates and placed on the workbench in the CVD reactor to deposit diamond films. According to the temperature distribution on substrates measured by thermocouple fixed in CVD reactor, the simulations were validated and the optimum arrangement of substrates was established from the simulation results. In addition, the simulation model was altered to optimize the process parameters of HFCVD deposition, and an improved process of depositing diamond films with high quality was obtained in order to achieve the great surface morphology, which laid the foundation of developing a new method to arrange the substrates in the CVD reactor for depositing diamond films.

High Speed Milling of SiC Particle Reinforced Aluminum-Based MMC with Coated Carbide Inserts

Metal matrix composites (MMC) have many advanced mechanical properties such as high wear resistance, low weight, high strength and stiffness, lower expansion coefficient and high thermal conductivity, which are widely used in the automotive, railway and aerospace industries. The main limit in MMC applications is the difficult machining, which leads to low production volumes and high machining costs. This study aims to investigate the machinability of MMCs and wear mechanism of cutting tools in the high speed machining processes. Cutting performances of SiC particle reinforced aluminum matrix composites are investigated through the high-speed end milling experiments with coated carbide inserts. Experiment results reveal the influences of cutting speed on cutting force, cutting temperature, surface roughness, surface micrograph, residual stress and tool wear. Cutting force, cutting temperature and surface roughness increase with cutting speed increasing. The machined surface quality is presented in the high speed milling of these MMCs with TiNAl-coated carbide inserts. Under the cutting speed of 10-40m/min, the feed rate of 0.02mm/tooth and the cut depth of 0.5mm, the better surface finish could be achieved. TiNAl-coated carbide inserts demonstrate good wear resistance even if SiC particle wear occurs. The conclusions are of great significance for high efficiency and quality machining of MMCs.

Surface Quality Studies with Respect to Grinding Burn of New Typical Nickel-Based Superalloy

Excessive grinding temperature leads to thermal damage that greatly deteriorates the surface quality and has an adverse effect on in-service strength and fatigue properties. Grinding burn is the common type of thermal damage that has been becoming the main conscious issue in grinding difficult-to-cut materials with regard to high efficiency and good integrity as well as high accuracy. Directionally solidified nickel-based superalloy DZ4 is a kind of very important structural material developed nowadays domestically, but the very poor machinability hinders its broad utilization in aircraft. This paper unveiled its grinding burn mechanism by experimentally analyses of grinding process characteristics such as grinding forces and grinding temperature, and also by metallurgical examinations for the surface integrity. With the onset of grinding burn, this paper gives the conclusions as follows. The critical grinding temperature is 950°C. The grinding force ratio Fn/Ft changes remarkably and can be used as the characteristic parameter for the real time grinding burn monitoring. There is no evident change in burn color from slight burn to severe burn, which is much different from that of carbon steel grinding. The residual tensile stress of burned surface layer is very high, and is almost 22 times as much as that of the normal case. The mechanical strength and heat resistance of the DZ4 alloy deteriorates obviously with the decrease of strengthening particles x92 phase. The large and irregularly distributed x92 phases in surface layer severely affect the coincidence of performance of DZ4. The surface hardness of DZ4 alloy weakens by 25% and the depth of affected layer exceeds 0.5mm. This paper will be beneficial to the catastrophic failure inspections and to the development of advanced grinding technologies related to avoidance of grinding burn.

Development of Diamond-Coated Drills for High-Speed Machining SiC Particles Reinforced Aluminum-Matrix Composite

Compared to sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills. Because of high performance in high speed machining non-ferrous difficult-to-cut materials in the field of automobiles industry, aeronautics and astronautics industry, diamond-coated drills find large potentialities in commercial applications. However, the poor adhesion of the diamond film on the substrate and high surface roughness of the drill flute adversely affect the tool life and machining quality and they become the main technical barriers for the successful development and commercialization of diamond-coated drills. In this paper, diamond thin films were deposited on the commercial WC-Co based drills by the electron aided hot filament chemical vapor deposition (EACVD). A new multiple coating technology based on changing gas pressure in different process stages was developed. The former large triangular faceted diamond grains may have great contribution to the adhesive strength between the film and the substrate, and the later overlapping ball like blocks consisted of nanometer sized diamond crystals may contribute much to the very low roughness of diamond film. Adhesive strength and quality of diamond film were evaluated by scanning electron microscope (SEM), atomic force microscope (AFM), Raman spectrum and drilling experiments. The ring-block tribological experiments were also conducted and the results revealed that the friction coefficient increased with the surface roughness of the diamond film. From a practical viewpoint, the cutting performances of diamond-coated drills were studied by drilling the SiC particles reinforced aluminum-matrix composite. The good adhesive strength and low surface roughness of flute were proved to be beneficial to the good chip evacuation and the decrease of thrust and consequently led to a prolonged tool life and an improved machining quality. The wear mechanism of diamond-coated drills is the abrasive mechanical attrition. Introduction Diamond has been regarded as the perfect cutting-tool material for its inherent properties such as extreme hardness, high thermal-conductivity, low thermal-expansion coefficient and high corrosion resistance. Diamond cutting tools are suitable for high speed machining non-ferrous difficult-to-cut materials such as high silicon aluminum alloys, SiC particles reinforced aluminum-matrix composites, titanium alloys, and engineering ceramics. Compared to the sintered polycrystalline diamond (PCD), the deposited thin film diamond has a great advantage on the fabrication of cutting tools with complex geometries such as drills, reamers, solid end milling cutters, and taps [1-2]. The electron aided hot filament chemical vapor deposition (EACVD) is a popular technology to fabricate the diamond cutting tools. Peeling of diamond film usually occurs due to lack of adhesive strength and yields very short tool life. If the surface roughness of diamond film is high, it will deteriorate the chip evacuation capability of the flutes and lead to overload of cutting tool, adversely affecting the tool life and machining precision and quality. Up to now, the poor adhesion of the diamond film on the substrate and high surface roughness are the main technical barriers for the successful development and commercialization of diamond-coated drills. WC-Co cemented carbide is the very common substrate for cutting tools. Unfortunately the Co plays as a catalyst for graphite formation during the EACVD process and will be destructive to the adhesion of the diamond coating on the substrate. Removal of the Co from the surface is very Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 853-857 doi:10.4028/www.scientific.net/KEM.259-260.853

Deposition and Application of CVD Diamond Films on the Interior-Hole Surface of Silicon Carbide Compacting Dies

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.

Study on the Effects of Substrate Grain Size on Diamond Thin Films Deposited on Tungsten Carbide Substrates

Three sets of Co-cemented tungsten carbide (94 wt.%WC-6wt.%Co) blades with different average grain size (0.5, 1.5 and 3 μm) were used as substrates. After usual acid etching and scratching with diamond powders, H2 gas etching decarburization by microwave plasma and cleaning in an ultrasonic bath of acetone solution, substrates with different WC grain size were placed in the electron aided hot filament chemical vapor deposition (EACVD) reactor to fabricate diamond thin films. Scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, indention tests and surface scanning profilometer showed that substrate grain size plays an important role in determining the performance of diamond films deposited on the tungsten carbide substrates such as film adhesive strength, film surface roughness and diamond film quality. The related conclusions were beneficial to the optimization of CVD diamond process and also to the metallurgical process of tungsten carbide.

Fabrication and Applications of Ultra-Smooth Composite Diamond Coated WC-Co Drawing Dies

Micro/nano-crystalline multilayered ultra-smooth diamond (USCD) films are deposited on the interior-hole surface of conventional WC-Co drawing dies with a combined process consisting of the hot filament chemical vapor deposition (HFCVD) method and polishing technique. Scanning electron microscopy (SEM), surface profilemeter, Raman spectroscopy and X-ray diffraction (XRD) are employed to provide a characterization of as-deposited USCD films. The results exhibit that as-deposited USCD films present an ultra-smooth surface, its surface roughness values (Ra) in the entry zone, drawing zone and bearing zone are measured as 25.7 nm, 23.3 nm and 25.5 nm respectively. Furthermore, the working lifetime and performance of as-fabricated USCD coated drawing dies are examined in producing copper tubes with hollow sinking, fixed plug and floating plug. The results show that the lifetime of USCD coated drawing is as more than 30 times as that of WC-Co drawing dies in the drawing process with hollow sinking, 7 times in the fixed plug drawing and 10 times in the floating drawing.

Effect of Boron Concentration on Adhesion and Cutting Performance of Diamond-Coated Cemented Carbide Tools

Diamond thin films doped with various boron concentrations were grown on WC-Co cemented carbide tools by hot-filament-assisted chemical vapor deposition (HFCVD). The trimethyl borate dissolved in acetone solution was used as the boron resource (B/C=0%, 0.1%, 0.3%, 0.5%). The surface morphology of diamond films with different boron contents was investigated by Scanning electron microscopy, the adhesive strength was calculated by means of indentation test under a load of 1500N. A real cutting performance was carried out on Al metal matrix composites material (20vol%SiC, 15μm), and the insert flank wear was examined by measuring the scars that appeared on the cutting edge with tool microscope. The research results shown the surface morphology and structure of the diamond films changed owing to boron doping. As the doping levels increased, the average grain size of the films decreased from 10 to 2μm. A significant improvement in adhesion and cutting performance were observed as the boron contents increased from 0% to 0.5%. The adhesion and cutting performance were best when the boron concentration was 0.3%. Adequate boron can effectively suppress the cobalt diffusion to the substrate surface and avoid the catalytic effect of cobalt at the high temperature. It is of great significance for improvement of the adhesive strength and cutting performance of diamond-coated tools using above method.

Studies on the Performance of Diamond Thin Films with Different Tungsten Carbide Substrates

In order to make sure the details of influences of grain size on the performance of diamond thin film, different trademarks of tungsten carbide tools with different scales of substrate grain size were selected. Scanning electron microscopy (SEM), Raman spectroscopy, indention tests and surface scanning profilometer showed that WC grain size played an important role in determining the performance of diamond films deposited on the tungsten carbide substrates. Therefore, an appropriate combination of pretreatments, substrate grain size and deposition parameters should be selected. The tribological pin-on-disc tests have been conducted. The quantitative relations between the friction coefficient and the surface roughness were investigated. The experimental results have shown that the surface roughness of diamond coatings has appreciable influences on the friction coefficient, especially on the initial friction. There exists an optimal value of surface roughness of diamond-coated tools with regard to cutting tool life.

Simulation of Substrate Temperature Distribution in Diamond Films Growth on Silicon Wafer by Hot Filament CVD

The substrate temperature has great influence on the growth rate and quality of diamond films by hot filament chemical vapor deposition (HFCVD). In order to deposit polycrystalline diamond films of uniform thickness over large areas and improve the growth rate of diamond films, the substrate temperature uniformity need to be further improved. Thus three-dimensional finite volume simulation has been developed to predict substrate temperature distribution, and optimize the deposition parameters like the size and arrangement of filaments which have a profound effect on the substrate temperature. Based on the simulation results, the optimum parameters of diamond deposition are found. Subsequently, experiments of depositing diamond films on silicon (100) wafers are done when the deposition parameters are fixed at optimum values gained from the simulation results. According to the results of scanning electron microscopy (SEM) and Raman spectroscopy, the thickness and quality of diamond films are homogeneous, which validate that the simulated deposition parameters are conducive to fabricate the high quality diamond films.