Sliding friction and wear of tin-, indium- and lead-coated 52100 steel

Abstract

The sliding friction and wear behavior of 52100 steel with and without soft metal coatings was studied by using a ball-on-disk test device in a vacuum environment. Coatings ranging from 0.01 μm to several micrometers were produced by thermal vapor deposition (tin, lead), ion-beam sputtering (tin, indium) and magnetron-sputtering deposition (tin). For an uncoated 52100 steel disk sliding against a 52100 steel ball, the friction coefficient increased from 0.2 to 0.7 as the normal load increased from 0.1 to 0.3 kgf. Both the disk and the ball became severely damaged as friction increased. For tests with coated specimens, the coefficient of friction at early stages of sliding was found to depend strongly on the morphology of the soft metal coatings. For example, coatings with granular structure, normally found in sputtered films thicker than 1 μm, gave rise to very high friction coefficients. The coefficient of friction of other coated specimens remained low after prolonged sliding, even when the soft metal coatings had worn from the disks. The coating material still contributed to reduced friction either by the formation of roller-type debris on the wear track or by the formation of a prow at the tip of the slider. For magnetron-sputtered tin films, a lower coefficient of friction resulted when only the disk was coated, rather than both sliding components.