Tribological behavior of ultra-thin soft metallic deposits on hard substrates

The tribological behavior of ultra-thin soft metallic deposits on silicon substrates was investigated for low load sliding applications. Thermal evaporation and ion-beam sputtering deposition techniques were used to produce coatings of various apparent thicknesses (1-1000 nm). Sliding tests were conducted with gold and silver coatings on silicon substrates using a reciprocating pin-on-flat type apparatus to study the tribological behavior of these coated specimens. Various tribological parameters were examined for controlling friction and wear of soft metallic coatings under relatively low loads. Experimental results indicate that the film thickness, load and coating deposition technique affect the frictional behavior of soft metallic coatings. Microscopic observations showed that plowing is the main cause of friction for soft metallic coatings under relatively low loads. Based on the experimental observations, the film thickness and load dependency of soft coatings were analyzed using the plowing friction model with a modified hardness term. This analysis shows that the film thickness and load dependency of soft coatings can be reasonably explained using the plowing model.