Selected fretting-wear-resistant coatings for Ti-6%Al-4%V alloy

Abstract

A Ti-6%Al-4%V alloy (Ti-6Al-4V), in the solution-treated overaged condition, was subjected to fretting exposures against uncoated Ti-6Al-4V as a baseline and against various coatings and surface treatments applied to Ti-6Al-4V. Fretting experiments were conducted in dry air and in saturated air by using a hemisphere of radius 4.7 mm on a flat surface. Typical conditions included a 1.47 N normal load, an 80 Hz frequency and a 70 μm amplitude at room temperature. The coatings evaluated included plasmasprayed tungsten carbide with 12% Co, aluminum oxide (Al 2O 3) with 13% titanium oxide (TiO 2), chromium oxide, aluminum bronze with 10% aromatic polyester, polymer-bonded polyimide, polyimide with graphite fluoride, polyimide with molybdenum disulfide (MoS 2) and methylphenylsiliconebonded MoS 2 and the surface treatments included a pre-oxidation surface treatment, a nitride surface treatment and a sputtered MoS 2 coating. Results of wear measurements on both the coated and the uncoated surfaces after 3 × 10 5 cycles indicated that the polyimide coating was the most wear resistant and caused the least wear to the uncoated surfaces. Increased exposure, however, showed a sharp increase in fretting wear rate after 10 6 cycles. Surface-nitrided Ti-6Al-4V fretted against a polytetrafluoroethylene-impregnated Al 2O 3-TiO 2 coating on Ti-6Al-4V resulted in immeasurable wear to both surfaces.