Nanocrystalline diamond coatings

Figure 13 illustrates the effectiveness of a nanocrystalline diamond-coated carbide insert in preventing edge wear and loss of sharpness... 

Fig. 13 Extent of wear damage on (a) uncoated and (b) nanocrystalline diamond coated tool inserts after machining of hypereutectic aluminum-silicon alloy.

In fact diamond can also be formed at low pressure. With the Chemical Vapor Deposition technique (CVD) diamond can be forced to grow on a substrate surface. As a rule a gas mixture, containing a hydrocarbon and hydrogen, is thermally activated by a combustion flame or plasma technique. Atomic hydrogen and carbon containing radicals are formed, a gas from which diamond starts to grow at a low pressure. In ref [39.8] a nanocrystalline diamond coating of this type is described. Deposition temperature was 900°C. 

F. Hollman, Micro- and Nanocrystalline Diamond Coatings with Extreme Wear Resistance and Ultra Low Friction, Dissertation, Uppsala University, 1997 ). Lovelock, Gaia a new look at life on Earth, 1982 and The ages of Gaia, 1988. Oxford University Press D. V. Hoyt, K. H. Schatten, The Role of the Sun in Climate Change, Oxford University Press, 1997... 

The same skepticism applies to nanocrystalline diamond that is reported to be harder than diamond single crystals (Sumiya and Irifune, 2007). Other cases in which rough surfaces may have skewed the measurements are TiN/SiN coatings (Kauffmann et al., 2005) and (AlMgB14 + TiB2) mixtures (Cook et al., 2000). 

Recently, new methods have been developed for depositing nanocrystalline diamond (NCD) coatings with a very smooth surface finish. In these methods, a higher than... 

Vadali. V. S. S. Srikanth, H. A. Samra, T. Staedler and X. Jiang, Nanocrystalline diamond/p-SiC composite interlayers for the deposition of continuous diamond films on W and Mo substrate materials, Surf. Coat. Technol, 201(22-23), 8981-85 (2007). 

Y. Tzeng, C. Liu, A. Hirata, Effects of oxygen and hydrogen on electron field emission Irom microwave plasma chemically vapor deposited microcrystalline diamond, nanocrystalline diamond, and glassy carbon coatings. Diam. Relat. Mat. 12(3-7), 456-463 (2003)... 

Specific conductive silicon substrates have to be carefully prepared before use. For the diamond-deposition process, substrates have to be cleaned, seeded with diamond nanocrystalline seeds at high surface density, and then coated with a grown thick diamond film (from less than 1 pm up to several p,m) by hot filament chemical vapor deposition (HF-CVD). At Adamant, deposition processes are performed automatically in programmable controlled process units, which allow growing diamond on scale up to 0.5 m2. The process is performed under low pressure (1 < 0.1 bar) and high temperature (filament temperature 2,500°C and substrate temperature 800-1,000°C) with a gas mixture composed of CH4, H2 (CH4/H2 ratio <1%), and a boron source (typically trimethyl boron). 

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