Diamond, friction behavior

Substances in this category include Krypton, sodium chloride, and diamond, as examples, and it is not surprising that differences in detail as to frictional behavior do occur. The softer solids tend to obey Amontons law with /i values in the normal range of 0.5-1.0, provided they are not too near their melting points. Ionic crystals, such as sodium chloride, tend to show irreversible surface damage, in the form of cracks, owing to their brittleness, but still tend to obey Amontons law. This suggests that the area of contact is mainly determined by plastic flow rather than by elastic deformation. 

Heimberg, J. A., Wahl, K. J., Singer, I. L., and Erdemir, A., "Friction Behavior of Diamond-like Carbon Coatings Time and Speed Effects, Appl. Phys. Lett., Vol. 78, 2001, pp. 2449-2451. 

Scharf, T. W. and I. L. Singer, I. L., Role of third bodies in friction behavior of diamond-like nanocomposite coatings studied by insSitu tribometry. Tribology Transactions, 45,2002, 363-371. 

Diamond behaves somewhat differently in that n is low in air, about 0.1. It is dependent, however, on which crystal face is involved, and rises severalfold in vacuum (after heating) [1,2,25]. The behavior of sapphire is similar [24]. Diamond surfaces, incidentally, can have an oxide layer. Naturally occurring ones may be hydrophilic or hydrophobic, depending on whether they are found in formations exposed to air and water. The relation between surface wettability and friction seems not to have been studied. 

Jia ZF, Xia YQ, Li JL et al (2010) Friction and wear behavior of diamond-fike carbon coating on plasma nitrided nrild steel under boundary lubrication. Tribol Int 43 474-482... 

Graphite is probably the most widely used lamellar solid lubricant. Unlike M0S2, graphite has a lower friction and lower wear in the presence of moisture than in vacuum. Therefore, graphite is not recommended for vacuum or high-temperature applications. But another form of carbon, amorphous hydrogenated carbon films (also called diamond-like carbon), has the reverse behavior It works extremely well in vacuum, but its friction coefficient is increased by the presence of moisture [37]. 

Examples of materials falling into this class include salts such as sodium chloride, diamond, sapphire and other similar minerals, and solid nonmetallic elements such as krypton. The softer members of the class are generally found to obey Amonton s laws with frictional coefficients falling in the range of 0.5-1.0. The harder, more brittle substances such as sodium chloride tend to suffer extensive surface damage due to cracking but still hold more or less to normal behavior. 

Micro-scale scratching of bulk Si by Bhushan and co-workers (1995) showed similar behavior to our scratch results on the unimplanted Si wafer. Using a much smaller probe (conical diamond with 1 p,m end radius) they observed (from friction... 

PVD coatings provide considerable potential in terms of the sliding behavior. The production of anti-wear and anti-friction coatings through PVD processes has become part of the state of the art. This allows a layer deposition on almost all substrate materials with almost any chemical composition. Metallic layers but also such as carbon, diamond, and diamond-like layers can be produced. The usual layer thicknesses range from 2 to 6 pm, and can be applied at temperatures of 150 to 500 °C. Low alloy steels can be coated without loss of hardness and good adhesion due to the low coating temperatures. 

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