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Diamond coating has many excellent properties as the same as those of the natural diamond, such as extreme hardness, high thermal conductivity, low thermal expansion coefficient, high chemical stability, and good abrasive resistance, which is considered as the best tool coating material applied to the high-silicon aluminum alloy cutting. We can use the hot filament chemical vapor deposition method (HFCVD) to deposit a 2–20 μm diamond coating on the cemented carbide tool to improve the cutting performance and increase the tool life significantly. Many experiments have proved that the existence of cobalt phase can weaken the adhesive strength of diamond coating. However, we still lack a perfect theory to explain why the Co element can reduce the adhesive strength of diamond coating is still lacking. What we can do now is only to improve the adhesive strength of diamond coating by doing testing many times in experiments. Compared with these traditional experiments, the first principles simulation based on quantum mechanics can describe the microstructure property and electron density of materials. It is successfully used to investigate the surface, interface, electron component, and so on etc. We can also use this method to study the interface problem at an atomic level. So the first principles based upon density functional theory (DFT) is used to investigate the influence of cobalt binding phase in cemented carbide substrate on adhesive strength of diamond coating. In this article, we uses Material Studios software to build WC/diamond and WC-Co/diamond interface models to evaluate the influence of cobalt phase on the adhesive strength of diamond coating with CASTEP program which can calculate the most stablest structure of film-substrate interface. We use PBE functional form to obtain the exchange potential and relevant potential, and to solve the self-consistent Kohn-Sham equations. We calculate the interfacial bonding energy, analyse the electron density of diamond coating and the bond Mulliken population of diamond film-substrate interface. The results show that the interfacial bonding energy of WC/diamond is 6.74 J/m2 and that of WC-Co/diamond is 5.94 J/m2, which implies that the adhesive strength of WC/diamond is better than that of WC-Co/diamond. We also find that Co element can transfer the charges near the interface of WC/diamond model when the magnetic Co element exists at the WC/diamond interface. As a result, the polarity of tungsten element in tungsten carbide and the polarity of carbon element in diamond coating near the interface turn to be identical polarity, and then the charge density of tungsten in cemented carbide changes from 0.430 e/A3 to 0.201 e/A3 and the charge density of Carbon in diamond changes from-0.045 e/A3 to 0.037 e/A3, and they exclude to each other, so the distance of interface becomes larger than that from the WC/diamond model, which changes from 2.069 Å to 3.649 Å. This can explain why the existence of Co element can weaken the adhesive strength of diamond coating. Meanwhile, Mulliken population analyses show that the bond strength of WC-Co /diamond at the interface is smaller than that of WC/diamond. So this can prove that the cobalt binding phase in cemented carbide substrate can weaken the adhesive strength of diamond coating, and then we need to do some pretreatments in order to reduce the cobalt binding phase in the cemented carbide substrate before depositing diamond coating.
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Keywords:
- diamond coating /
- Co binding phase /
- adhesive strength /
- first principle
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[2] Straffelini G, Scardi P, Molinari A, Polini R 2001 Wear. 249 1020
[3] Shen B, Sun F H 2009 Diamond Relat. Mater. 18 238
[4] Liu M N, Bian Y B, Zheng S J, Zhu T, Chen Y G, Chen Y L, Wang J S 2015 Thin Solid Films 584 165
[5] Wang X C, Lin Z C, Shen B, Sun F H 2014 Trans. Nonferrous Met. Soc. China 24 3181
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[19] Song Y, Xing F J, Dai J H, Yang R 2014 Intermetallics. 49 1
[20] Tang J, Zhang G Y, Bao J S, Liu G L, Liu C M 2014 Acta Phys. Sin. 63 187101 (in Chinese) [唐杰, 张国英, 鲍君善, 刘贵立, 刘春明 2014 63 187101]
[21] Peng Y Z, Huo D X, He H P, Li Y, Li L W, Wang H W, Qian Z H 2012 Journal of Magn. Magn. Mater. 324 690
[22] Pan J W, Li C, Zhao Y F, Liu R X, Gong Y Y, Niu L Y, Liu X J, Chi B Q 2015 Chem. Phy. Lett. 628 43
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[1] Jian X G, Shi L D, Chen M, Sun F H 2006 Diamond Relat. Mater. 15 313
[2] Straffelini G, Scardi P, Molinari A, Polini R 2001 Wear. 249 1020
[3] Shen B, Sun F H 2009 Diamond Relat. Mater. 18 238
[4] Liu M N, Bian Y B, Zheng S J, Zhu T, Chen Y G, Chen Y L, Wang J S 2015 Thin Solid Films 584 165
[5] Wang X C, Lin Z C, Shen B, Sun F H 2014 Trans. Nonferrous Met. Soc. China 24 3181
[6] Wei Q P, Ashfold M N R, Mankelevich Y A, Yu Z M, Liu P Z, Ma L 2011 Diamond Relat. Mater. 20 641
[7] Deng F M, Wang Q, Zou B, Zhang D, Lu S T, Zhao X K 2013 Cemented Carbide 30 113 (in Chinese) [邓福铭, 王 强, 邹 波, 张 丹, 陆绍悌, 赵晓凯 2013 硬质合金 30 113]
[8] Wei Q P, Yu Z M, Ma L, Yang L, Liu W P, Xiao H 2008 Chin. J Nonferrous Met. 18 1070 (in Chinese) [魏秋平, 余志明, 马莉, 杨莉, 刘王平, 肖和 2008 中国有色金属学报 18 1070]
[9] Li G, Zhao Y G, Zheng R, Ni J, Wu Y N 2015 Chin. Phy. B 24 087302
[10] Meng F S, Li J H, Zhao X 2014 Acta Phys. Sin. 63 237102 (in Chinese) [孟凡顺, 李久会, 赵星 2014 63 237102]
[11] Li T F, Liu T M, Wei H M, Hussain S H, Miao B, Zeng W, Peng X H 2015 Comput. Mater. Sci. 105 83
[12] Ullah M, Ahmed E, Hussain F, Rana A M, Raza R 2015 Appl. Surf. Sci. 334 40
[13] Zhang L 2009 M. S. Dissertation (Jinan: Shangdong University) (in Chinese) [张路 2009 硕士学位论文(济南: 山东大学)]
[14] Jian X G, Zhang Y H 2015 Acta Phys. Sin. 64 046701 (in Chinese) [简小刚, 张允华 2015 64 046701]
[15] Jian X G, Zhang Y H 2015 Diamond & Abrasives Engineering 34 23 (in Chinese) [简小刚, 张允华 2015 金刚石与磨料磨具工程 34 23]
[16] Wang Q J, Tan Q H, Liu Y K 2015 Comput. Mater. Sci. 105 1
[17] Wang L L, Wan Q, Hu W J, Zhao X P 2010 Comput. Appl. Chem. 27 6 (in Chinese) [王丽莉, 万强, 胡文军, 赵晓平 2010 计算机与应用化学 27 6]
[18] Chen B S, Li Y Z, Guan X Y, Wang C, Wang C X, Gao X Y 2015 Comput. Mater. Sci. 105 66
[19] Song Y, Xing F J, Dai J H, Yang R 2014 Intermetallics. 49 1
[20] Tang J, Zhang G Y, Bao J S, Liu G L, Liu C M 2014 Acta Phys. Sin. 63 187101 (in Chinese) [唐杰, 张国英, 鲍君善, 刘贵立, 刘春明 2014 63 187101]
[21] Peng Y Z, Huo D X, He H P, Li Y, Li L W, Wang H W, Qian Z H 2012 Journal of Magn. Magn. Mater. 324 690
[22] Pan J W, Li C, Zhao Y F, Liu R X, Gong Y Y, Niu L Y, Liu X J, Chi B Q 2015 Chem. Phy. Lett. 628 43
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