H.S. Shen

Improvement of adhesive strength and surface roughness of diamond films on Co-cemented tungsten carbide tools

Abstract Diamond-coated tools were fabricated using Co-cemented carbide inserts as substrates by the bias-enhanced hot filament chemical vapor deposition. The surface of the WC–Co substrate was decarburized by microwave plasma with Ar–H2 gas. Effect of the new substrate pretreatment on the adhesion of diamond films was investigated. A boron-doped solution was brushed on the tool surface to diffuse boron into the substrates during diamond deposition. A new process was used to lower the surface roughness of diamond thin films by appropriately controlling acetone concentration and reactive gases pressure. It consists of a two-step chemical vapor deposition procedure that includes, first, the deposition of the rough polycrystalline diamond and then the fine-grained diamond. The research results show that the pretreatment using Ar–H2 etching decarburization by microwave plasma is an effective method to enhance adhesive strength. An adequate amount of boron dopant solution can effectively suppress the cobalt diffusion to the surface and avoid the catalytic effect of Co at the high temperature. Smooth diamond films with low roughness can be deposited by the two-step CVD process. It is of great significance for improvement of the cutting performance of diamond-coated tools using the above new technology to deposit diamond coatings with the low surface roughness and high adhesive strength on WC–Co substrates.

Fabrication and application of chemical vapor deposition diamond-coated drawing dies

Abstract A diamond coating has been fabricated by straight hot filament chemical vapor deposition (CVD) passing through the interior hole of the drawing die using a mixture of hydrogen and acetone as source gases. The substrates are drawing dies made by cemented carbides with large apertures (φ>2 mm), and are pre-treated by various methods including leaching Co by acid solution, scratching the substrate by diamond powder and decarburizing the WC substrate by microwave plasma. The homogeneity of coatings is estimated by scanning electron microscopy and Raman spectroscopy. The preliminary applied tests show that the adhesion strength of diamond coatings can meet the need of the practical drawing wires. As compared with the cemented carbide drawing die, the working lifetime of the diamond-coated drawing die can be increased by a factor of five to 10.

Fabrication and application of high quality diamond-coated tools

Abstract Diamond-coated tools were fabricated using Co cemented carbide inserts as substrates by electronically aided hot filament chemical vapor deposition (EACVD). An amount of additive in an acid solution was used to promote the Co etching of the substrate surface. The surface of the WC–Co substrate was decarburized by microwave plasma with Ar–H 2 gas. The effect of the new substrate pre-treatment on the adhesion of the diamond films was investigated. A boron-doped solution was brushed on to the tool surface to diffuse the boron into the substrate during diamond deposition. A new process was used to reduce the surface roughness of the diamond thin films by appropriately controlling the deposition parameters, which consists of a composite diamond film chemical vapor deposition procedure including first the deposition of rough polycrystalline diamond and then fine-grained diamond. The research results show that the pre-treatment, including both Co etching in acid solution and Ar–H 2 etching decarburization by microwave plasma, is an effective method to enhance the adhesive strength. An adequate amount of boron dopant solution can effectively suppress cobalt diffusion to the surface and avoid the catalytic effect of Co at high temperature. The composite film CVD process can deposit smooth diamond films with low surface roughness. It is of great significance for the improvement of the cutting performance of diamond-coated tools to use the above new technology to deposit diamond coatings with low surface roughness and high adhesive strength on WC–Co substrates.

Pre-treatment for diamond coatings on free-shape WC–Co tools

Abstract A new multiple chemical pre-treatment including microwave oxidation, reaction in alkaline solution and cleaning by ultrasonic treatment in acid solution has been performed for free shape cemented WC–Co tools in order to increase the diamond nucleation and to enhance the coating adhesion. High quality diamond films were deposited on such pre-treated substrates by a hot filament chemical vapor deposition (CVD) method using a mixture of acetone and hydrogen gases. After pre-treatment, the surface of the WC–Co substrate becomes slightly rough, but its composition or structure shows no changes identified by X-ray diffraction (XRD). Scanning electron microscopy (SEM) indicates a distribution of uniform micro-roughness WC grains on substrate surface. The results show that the multiple chemical pre-treatment effectively increases the diamond nucleation as well as greatly enhancing the coating adhesion. Especially, it is suitable for free-shape substrates, which may open the way to the use of diamond coatings for coated tool applications.

Composite diamond films with smooth surface and the structural influence on dielectric properties

Composite diamond films with a smooth surface were achieved by the deposition of alternate conventional polycrystalline diamond and nanocrystalline diamond layers. The morphology and structure of the composite films were evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy. The conduction dependence of the temperature and the electrical field and the dielectric loss dependence of the frequency in the composite diamond films were studied. The probable conduction mechanism was attributed to the space charge limited currents (SCLC). The result shows that the surfaces of the composite films were very smooth, and the films have better dielectric properties that were similar to conventional polycrystalline diamond films. They possess superior properties of conventional and nanocrystalline diamond films, and could be applied to the fabrication of diamond semiconductor devices.

Growth of CVD heteroepitaxial diamond on silicon (001) and its electronic properties

Abstract Microwave CVD heteroepitaxial diamond film on a 4° off-axis Si(100) substrate is obtained by two stages. The first one is to grow oriented 3c-SiC layers on Si(100) using a non-toxic and non-inflammable (CH3)6Si2NH organic compound carried by hydrogen. The following stage is to grow oriented diamond films on them under the atmosphere of CH4 and H2. In each stage there are bias and growth processions. The micro-Raman and micro-Auger analyses prove that there is a perfect orientation relationship between the film and substrate as following: diamond 〈001〉//3c-SiC〈001〉//Si〈001〉. The Hall effect indicates that the film is a P type, whose resistivity is 9.4×10−3 Ω cm, the Hall coefficient is 2.9 cm3/Q, the hole mobility is 309 cm2/V s and the carrier concentration reaches 2.2×1018 cm−3.

Surface structure characterization of WC-Co substrate by hot filament radiation in diamond film growth

Abstract Structural changes and surface morphology have been characterizeded by X-ray diffraction, SEM and Raman spectroscopy for the surface of WC-Co substrates, which were preheated by direct radiation from Ta or W filaments under a pure hydrogen atmosphere. A thin diamond film was then deposited on the substrates in a hot filament CVD apparatus under an acetone and hydrogen atmosphere. It was found that the surface structure is very sensitive to the treatment conditions. The hot filament evaporation is beneficial in removing elemental Co in the substrate and enhancing the diamond quality as well as the adhesion.