Abstract
The distribution of substrate temperature plays a decisive role on the uniformity of polycrystalline diamond films on cemented carbide tools with a long flute, prepared by a hot filament chemical vapor deposition (HFCVD). In this work, the heat dissipation mode at the bottom of tools is a focal point, and the finite volume method (FVM) is conducted to simulate and predict the temperature field of tools, with the various materials of the holder placed under the tools. The simulation results show that the thermal conductivity of the holder affects the temperature difference of the individual tools greatly, but only affects the temperature of different tools at the same XY plane slightly. Moreover, the ceramic holder can reduce the difference in temperature of an individual tool by 54%, compared to a copper one. Afterwards, the experiments of the deposition of diamond films is performed using the preferred ceramic holder. The diamond coatings on the different positions present a highly uniform distribution on their grain size, thickness, and quality.
Highlights
Chemical vapor deposition (CVD) allows diamond films to deposit directly and conveniently on different shapes of substrates, making possible the use of the many excellent mechanical properties of diamond films in a wide field of industrial applications [1,2]
In Ref. [13,14,15] we proposed a simulation method based on the finite volume method (FVM), coupling all means of heat transfer mechanisms and adopting a three-dimensional model well in accordance with the actual reactive chamber, and optimized the uniformity of the temperature field generated on the flat substrates by changing the filament arrangements
In order to simplify the simulation, the following assumptions are made: (1) the working pressure in the reaction chamber is constant; (2) the simulated gas is considered only hydrogen, because the methane content in the actual deposition process is very low; (3) no chemical exothermic reaction occurs in the reaction chamber; (4) The miscellaneous curves of the flute of the milling cutter increase the difficulty of meshing surface and greatly increase the amount of calculation
Summary
Chemical vapor deposition (CVD) allows diamond films to deposit directly and conveniently on different shapes of substrates, making possible the use of the many excellent mechanical properties of diamond films in a wide field of industrial applications [1,2]. [13,14,15] we proposed a simulation method based on the finite volume method (FVM), coupling all means of heat transfer mechanisms (radiation, conduction, and convection) and adopting a three-dimensional model well in accordance with the actual reactive chamber, and optimized the uniformity of the temperature field generated on the flat substrates by changing the filament arrangements. As the flute is over 30 mm, the diamond coatings on the tools shows an extreme non-uniformity along the axis of tools, due to an obvious temperature gradient along the tool tip toward the tool shank This is because the substrate and its surrounding temperature decay rapidly with the distance from the center temperature generated from the hot filaments, and the filaments are usually located near the tip of the tools. A preferred material of platform is selected, with which an actual deposition experiment of diamond coated milling cutters is conducted to verity the correctness of simulation results
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