X.C. He

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.

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.

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.

Diamond film improvement on WC-Co substrate by sputtering interface

To enhance the adhesion of diamond film on WC-Co substrate, interface of TiC and SiC by sputtering technique were introduced between them. The film structure and surface morphology have been checked by x-ray diffraction, Raman spectroscopy and SEM. The adhesion between both coating and substrate have been evaluated by cutting test. In addition, the vertical tensile test has been carried out to measure the adhesion strength, which indicated that the introduce of the interface layer played important effect for improvement of the film adhesion strength.

Evaluation of diamond-coated tool adhesion by indentation test

At present, the biggest problem with diamond coatings as applied to cutting tools is their poor adhesion strength to the substrates. Many substrate treatment as well as growth conditions have been tried to improve the adhesion strength. To evaluate these efforts, utilizing the indentation test is the better way for indentation application. A detailed discussion has been done in this paper.