Vol. 54 No. 6

Material Science and Technology of Japan, 54㸦2017㸧211㹼216

19Regular Paper
Fabrication of Boron-Doped Diamond Films on Cemented TungstenCarbide
Kunio SAITO1,2*, Atsuo KAWANA1, Asuka SUZUKI2 and Yukihiro SAKAMOTO3
1Japan Coating Center Co., Ltd, 1-43-34 Komatsubara, Zama, Kanagawa 252-0002, Japan

2Chiba Institute of Technology graduate school, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan

3Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan

Received Aug. 18, 2017; accepted for publication Oct. 23, 2017
Abstract
Diamond coating on cemented tungsten carbide (WC-Co) is quite difficult. Generally, in order to reduce reactivity ofcobalt (Co) which is the binder of WC-Co, the pretreatment using the acid is carried out. To obtain boron-doped
diamond (BDD), diborane (B2H6) and trimethyl boron (B(CH3)3) are often used as boron sources. This study is anattempt to deposit BDD directly on WC-Co by microwave plasma CVD using trimethyl borate (B(OCH3)3) as a safeboron source. WC-Co substrate was scratched with diamond powders and cleaned before loaded into the chamber.
B(OCH3)3 was introduced into the chamber with hydrogen (H2) carrier gas. Boride was formed on the substrate toreduce reactivity of Co. Then, BDD was formed continuously with using reactive gases of methane (CH4) and H2. As
a result, the presence of boride was important to secure adhesion strength and deposit of BDD. It was possible todeposit BDD continuously with good adhesion without Co removal as a pretreatment.
Keywords: Boron-doped diamond, microwave plasma CVD, Cemented tungsten carbide, Adhesion

1.

Introduction

WC-Co. This is because the catalytic function of Co serves as aWC-Co having heat resistance and abrasion resistance isbinder of WC-Co, and in order to control this action, generally,

widely applied to cutting tools as well as general tools. Generally,

pretreatment of removal with acid is performed [4]. On the othertungsten carbide (WC) particles are sintered together with ahand, it has been reported that without removing Co with acid,binder metal, but the kind and amount of the binder and the WC

and by forming boride on the surface of WC-Co with the Plasma

particle diameter are changed depending on the application. The

Enhanced (PE) CVD using B2H6, reactivity of Co is controlled

pursuit of production efficiency made the processing conditions

and adhesion of nanostructure diamond improves [5]. Both B2H6

more stringent, in which it became common to coat Titanium (Ti)and B(CH3)3, which are commonly used as B sources, haveand Chromium (Cr) ceramic with physical vapor deposition

toxicity, flammability and explosiveness, and they need to be(PVD) after selecting an appropriate WC-Co [1-2].

managed by using special apparatus [6].

In recent years, the introduction of aluminum (Al) alloy andIn this study, B(OCH3)3 with a little toxicity was used as acarbon fiber reinforced plastic (CFRP) has been increasing forboron source. BDD was deposited on WC-Co directly using

the purpose of reducing weight mainly in the aerospace industry.

microwave plasma CVD with two steps formation of boride andHowever, adhesion and significant abrasion of the work piece ondeposit. It was inspected whether it was possible to secure thethe tool surface have become a major issue. In this processing,adhesion by forming boride on WC-Co surface even if it does not

ceramic coating cannot work and the only solution is diamondtake Co of a binder out by the acid.

coating [3].

2.

Although diamond coating is deposited by chemical vapor

Experimental method

2.1 Deposition of diamonddeposition (CVD), it is difficult to directly deposit diamond on* Corresponding author: kunio_saito@jcc.tocalo.co.jp(211)