Bonding CVD Diamond to WC-Co by High Pressure - High Temperature Processing
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Bonding CVD Diamond to WC-Co by High Pressure - High Temperature Processing Naira Maria Balzaretti1, Altair Soria Pereira1,2, Rafael Vieira Camerini1,2, Sérgio Ivan dos Santos1, and João Alziro Herz da Jornada1,3 1 Physics Institute, Federal University of Rio Grande do Sul, Av. Bento Goncalves, 9500, CP 15051, Porto Alegre, RS, 91501-970, Brazil 2 Engineering School, Federal University of Rio Grande do Sul, Av. Bento Goncalves, 9500, Porto Alegre, RS, 91501-970, Brazil 3 INMETRO, Rua Santa Alexandrina, 416, Rio de Janeiro, RJ, 20261-232, Brazil
ABSTRACT In this work we investigate the effect of processing at high pressure-high temperature (HPHT) on the adhesion of CVD diamond coatings on WC-Co substrates. The samples consisted of WC-Co substrates coated with thin diamond films (10 – 40 µm thick) grown by microwave plasma (MWCVD) CVD. The substrates were previously etched in order to remove the Co from the surface region. The adhesion of the film and its wear resistance improved after the HPHT treatment. SEM images of the cross section of the coated substrate revealed that Co infiltrated back to the region where it was previously removed. The results indicate that it is possible to take advantage of the HPHT plants already available around the world to produce, besides PCD’s and diamond powder, high-performance CVD diamond cutting tools with the advantage of requiring less demanding processing conditions. INTRODUCTION The outstanding mechanical and thermal properties of diamond combined to the toughness of a tungsten carbide substrate enable the production of cutting tools of excellent performance [1-2]. Diamond coated cutting tools can be produced with CVD diamond technology either by direct deposition of the diamond film over the substrate or by brazing a free standing CVD diamond film on the substrate surface under vacuum at high temperatures. However the adhesion between the film and the substrate is the major challenge for the development of technological applications. In the field of diamond tools for machinery applications, HPHT processing is currently used for synthesis of diamond powder and for the production of polycrystalline diamond compacts (PCD) by sintering diamond grains using a metallic binder. In this work we explore the effect of HPHT processing on the properties of CVD diamond coated WC-Co substrates. The advantages of HPHT processing are related to the thermodynamic conditions where diamond is the stable phase of carbon [3] and to the increase of the mechanical grip at the interface, eliminating voids. In a previous paper, it was shown that it is possible to induce a strong adhesion between a free standing thick diamond film and a WC-Co substrate after processing at pressures above 4 GPa and temperatures above 1100°C [4]. In this work it was investigated the influence of HPHT processing over the adhesion and wear resistance of a thin diamond film grown directly over a WC-Co substrate.
EXPERIMENT Diamond films Before diamond deposition, the surface of the WC- 6 wt% Co substrate wa
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