Abstract
Epitaxial growth of diamond films on different facets of synthetic IIa-type single crystal (SC) high-pressure high temperature (HPHT) diamond substrate by a microwave plasma CVD in CH4-H2-N2 gas mixture with the high concentration (4%) of nitrogen is studied. A beveled SC diamond embraced with low-index {100}, {110}, {111}, {211}, and {311} faces was used as the substrate. Only the {100} face is found to sustain homoepitaxial growth at the present experimental parameters, while nanocrystalline diamond (NCD) films are produced on other planes. This observation is important for the choice of appropriate growth parameters, in particular, for the production of bi-layer or multilayer NCD-on-microcrystalline diamond (MCD) superhard coatings on tools when the deposition of continuous conformal NCD film on all facet is required. The development of the film morphology with growth time is examined with SEM. The structure of hillocks, with or without polycrystalline aggregates, that appear on {100} face is analyzed, and the stress field (up to 0.4 GPa) within the hillocks is evaluated based on high-resolution mapping of photoluminescence spectra of nitrogen-vacancy NV optical centers in the film.
Highlights
High hardness and abrasion resistance of diamond make it indispensable for machining of many materials such as composites and abrasive alloys, which leads to widespread use of diamond-based tools
We demonstrated that the morphology of diamond films grown by a microwave plasma chemical vapor deposition (CVD) on single crystal diamond substrates in CH4 -H2 -N2 in presence of high concentration of nitrogen strongly depends on the substrate’s crystallographic plane
{311} faces has been examined with scanning electron microscope (SEM), Raman and PL spectroscopy after a short (5 min) and prolonged (70 min) deposition time at conditions typically facilitated the formation of nanocrystalline diamond on foreign substrates
Summary
High hardness and abrasion resistance of diamond make it indispensable for machining of many materials such as composites and abrasive alloys, which leads to widespread use of diamond-based tools. WC-Co cutting tools allow a great improvement in the tool performance by extending its lifetime, increasing the machining speed, and providing a better quality of the machined material [1]. The application of bilayered or multilayered micro- and nanocrystalline DCs further enhances the cutting tools’ functional properties [2,3]. The upper nanocrystalline layer provides low roughness and low friction coefficient, as well as high bending strength [4]. The bottom layer is typically deposited in the microcrystalline diamond growth regime since it has better adhesion to the WC-Co substrate, Crystals 2017, 7, 166; doi:10.3390/cryst7060166 www.mdpi.com/journal/crystals. Compared with single-layer DCs, bilayered DCs have higher heat conductivity and increased resistance to cracking [6]
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