Tribology of UHMWPE film on air-plasma treated tool steel and the effect of PFPE overcoat

The effects of air-plasma treatment, film thickness, normal load and sliding speeds on the tribological properties of a thin film of Ultra-High Molecular Weight Polyethylene (UHMWPE) coated onto a tool steel substrate sliding against a Φ4 mm silicon nitride ball was investigated. Wear tests are carried out on a ball-on-disk tribometer. Air-plasma treatment has enhanced the adhesion of the polymer film to the steel substrate which led to an increased wear life (> 100,000 cycles) and low coefficient of friction (~ 0.14) of the thin film. A film of optimum thickness of 16.3 ± 2 μm shows the maximum wear resistance. The effect of varying loads (0.3, 1, 2 and 4 N) and speeds (200, 400, 600, 1000 and 2000 rpm) on wear life and coefficient of friction were also studied. The dual-film (UHMWPE/PFPE) on the air-plasma pre-treated tool steel surface further increased the wear life (> 200,000 cycles) at a load of 4 N and a rotational speed of 1000 rpm.