超硬合金へのボロンドープダイヤモンドの生成

抄録

Diamond coating on cemented tungsten carbide（WC-Co）is quite difficult. Generally, to reduce the reactivity of cobalt（Co）, which is the binder of WC-Co, an acid pretreatment is applied. Recent reports have described that the adhesion of nanostructured diamond coating was improved using diborane（B₂H₆）to reduce the reactivity of Co as a catalyst. To obtain boron-doped diamond（BDD）, B₂H₆ and trimethyl boron（B（CH₃）₃）are often used as boron sources. However, special apparatus must be prepared because of the toxicity, flammability, and explosiveness of these sources.

This study was conducted to deposit BDD directly on WC-Co using microwave chemical vapor deposition with trimethyl borate（B（OCH₃）₃）as a boron source. B（OCH₃）₃, a mixture of boric acid（H₃BO₃）and methanol（CH₃OH）, was introduced into the vacuum chamber with hydrogen（H₂）carrier gas. The WC-Co substrate was scratched with diamond powders and was cleaned with ultrasonic cleaner before loading into the chamber. Boride was formed on the substrate to reduce the reactivity of Co. BDD was formed continuously using reactive gases of methane（CH₄）and H₂, after forming borides. The presence of BDD was evaluated using SEM, Raman spectroscopy, and XPS. Evaluation using Rockwell hardness testing confirmed that the adhesion strength was secured through adhesion. Results suggest that the use of boride is important to secure adhesion strength and deposition of BDD, which can be done continuously with good adhesion and without Co removal as a pretreatment.