Acid Pretreatment of WC-Co Prior to CVD Diamond Coating M.Y. Noordin 1,a , A.S. Noor Adila 1,b , S. Izman 1,c and D. Kurniawan 1,d 1 Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, Skudai, Malaysia a noordin@fkm.utm.my Keywords: Tungsten carbide; cobalt removal, acid pretreatment, surface roughness. Abstract. Pretreatment on tungsten carbide (WC-Co) surface is critical for obtaining perfectly adherent diamond coatings by chemical vapor deposition (CVD). The carbide surface should have high roughness to facilitate diamond nucleation and adhesion. The presence of cobalt—common binder for tungsten carbide—on the surface to be coated should be made minimum since it has negative influence on the diamond deposition process. In this study, surface pretreatment on tungsten carbide using sulfuric acid was evaluated in terms of the resulted cobalt removal and the surface roughening. The variables included were acid concentration, reaction temperature, and reaction time. The resulted surface roughness was 29% higher than initial, averaged at 1.07 µm. The acid pretreatment was also found effective in eliminating surface cobalt. Introduction Thin diamond films are prospective coatings for tools and die considering their superior properties in hardness and wear resistance as well as having low coefficients of friction and thermal expansion [1]. For the substrate material, cemented tungsten carbide is a popular option for these applications. Its combination of high hardness and toughness characteristics lead to its status as the dominant cutting tool material in the global market [2]. Introduction of diamond film synthesis at low pressure and less extreme temperature by chemical vapor deposition (CVD) makes direct deposition of diamond polycrystals on a cemented carbide substrate possible. Available CVD diamond coated carbide tools are deemed suitable for processing non-ferrous metals and alloys, ceramics, polymers, and composites [1,3]. Proper adhesion of the diamond polycrystals coating with the carbide substrate is the fundamental requirement to ensure the coated tool’s consistent performance [4]. Previous work on this diamond coating and carbide substrate recommends these practices for obtaining improved diamond coating-carbide substrate adhesion [4-5]: 1. Use low-cobalt substrate material. 2. Roughen the substrate’s surface. 3. Set deposition process at low substrate temperature. 4. Encourage high diamond deposition rate. Reason behind recommendation to use low cobalt substrate material is because carbon’s solubility in cobalt. During deposition process, this results in growth of non-diamond or graphitic phases [3,5,6]. These phases act as non adhering interlayer. They are also responsible for low rate of diamond deposition [5]. Considering these deteriorating influences, cobalt content within the substrate should be kept minimal. It should be noted that usually the cobalt content is readily set forth or recommended according to applications, considering its proportionality to the carbide’s toughness [5]. Thus, for cases such as this, the alternative is by removing cobalt content at carbide substrate’s surface. Adhesion of diamond polycrystals to carbide substrate is mainly by mechanical interlocking mechanism [3,5]. Accordingly, the purpose of surface roughening of the carbide substrate is to provide anchoring sites for the diamond polycrystals [3]. In order to obtain both cobalt removal and surface roughening, pretreatment of the carbide substrate should be performed prior to deposition processes. Pretreatment by acid etching is common method for these purposes. In this study, acid pretreatment by sulfuric acid is explored. $GYDQFHG 0DWHULDOV 5HVHDUFK 9RO SS 2QOLQH DYDLODEOH VLQFH 2FW DW ZZZVFLHQWLILFQHW 7UDQV 7HFK 3XEOLFDWLRQV 6ZLW]HUODQG GRLZZZVFLHQWLILFQHW$05 $OO ULJKWV UHVHUYHG 1R SDUW RI FRQWHQWV RI WKLV SDSHU PD\ EH UHSURGXFHG RU WUDQVPLWWHG LQ DQ\ IRUP RU E\ DQ\ PHDQV ZLWKRXW WKH ZULWWHQ SHUPLVVLRQ RI 773 ZZZWWSQHW ,'