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Platinum Metals Rev., 1989, 33, (2), 72

Tribological Properties of Thin Platinum Coatings

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It is known that the sliding wear behaviour of hard metals can be improved by coating one or both of the contacting surfaces with a thin layer of a soft metal, but this advantage can be lost by, for example, the formation of oxide or corrosion products. Therefore platinum with an annealed hardness of 48Hv and notable environmental stability would appear to be a suitable material for tribological applications, and the results of an investigation carried out at the National Institute for Materials Research, C.S.I.R., Pretoria, support this assumption (“The Use of Platinum in Thin Tribological Coatings”, A. Wells and D. J. de Wet, Wear, 1988, 127, (3), 269–281).

Their wear tests were carried out using a ballon-flat rig; however the applied load was higher than that normally used for such tribological experiments. Alumina or steel spheres were used, the latter in both the uncoated condition and after sputter ion plating with platinum. The flat steel specimens were in the uncoated condition, or coated with platinum by sputtering, or by deposition from fused salt or aqueous electrolytes.

Both lubricated and dry surfaces were investigated in air at room temperature, and representative results are presented. Alumina sliders rapidly eroded thin platinum coatings, however on sliding steel surfaces the use of platinum reduced the coefficient of friction and the wear damage, and it is concluded that when the topography of the surface provides sinks for wear debris and reservoirs for lubricants, the use of thin platinum coatings on steel can provide excellent sliding properties.

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