Table 3 – Tested VRR roller-pair configurations. Configuration Upper roller Lower roller 1 440F ; annealed ; passivated Ti6Al4V ; anodized 2 440C ; hardened ; passivated Ti6Al4V ; anodized 3 polyimide Ti6Al4V ; anodized 4 440C ; hardened ; passivated;  bonded PTFE solid lubeTi6Al4V ; anodized 5 440C ; hardened ; passivated Ti6Al4V ; PEO; bonded solid lube 6 440C ; hardened ; passivated Ti6Al4V ; (WC)aC:H DLC 7 440C ; hardened ; (TiC)aC:H DLC Ti6Al4V; (TiC)aC:H DLC 8 440C ; hardened ; passivated ;  nanocomposite MoS 2Ti6Al4V ; anodized 9 440C ; hardened ; passivated ;  nanocomposite MoS 2Ti6Al4V ; anodized;  nanocomposite MoS 2 10440C ; hardened ; passivated ;  nanocomposite MoS 2Ti6Al4V ; anodized;ultrasonic  smoothing nanocomposite MoS 2

Experiment Procedures and Results Experiment Procedures   The upper roller material for one test was made was polyimide material, otherwise the upper roller was  440 steel. The upper roller in all cases had a 400-mm crown radius and had a width of 13 mm. The lower roller for all testing was made from Ti6Al4V, had a flat profile, and had a width of 16.5 mm. Rollers were tested in a “tribologically clean" condition. For cases of rollers that had a coating by sputtering or physical  vapor deposition, the rollers were stored in vacuum-sealed bags immediately following deposition and  then were opened just prior to installation, and so special cleaning was not required. For cases of rollers  with hard surfaces, rollers were scrubbed using 0.05-micron alumina powder suspended in deionized water.  After appropriate scrubbing the roller was rinsed in deionized and filtered water. The cleaning procedure was different for the cases of the polyimide roller and the roller with the bonded type lubricant film. Alumina powder was not used to avoid possibility to imbed the powder into the relatively soft materials. In these cases, the rollers were cleaned using isopropanol rinse followed by ultrasonic cleaning in deionized water. It was confirmed that surfaces were clean of all oils by checking for uniform and full wetting of the surfaces. Water was then removed using dry, pressurized nitrogen. Once cleaned, the rollers were handled only with gloved hands and were transported to the rig using closed glass jars.  Just prior to installation, the surface textures of rollers were documented by tracing with a stylus  profilometer using a 2-micrometer-radius conisphere-tipped stylus. Traces were recorded in the both  circumferential (rolling) direction and in the profile (axial) direction. The final step prior to installing rollers  into the test chamber was to measure the mass using a scale with 0.0001 gram resolution. After installing  the rollers onto the test shafts, the hinged chamber door was immediately closed and the vacuum system operated to bring the chamber to a partial pressure of 6.7 Pa (50 x10 -3 torr) within one minute. The test  chamber was then brought to a pressure of 1x10-3Pa (7.5 x10-6torr) or less before beginning testing of  the rollers. Roller mass and stylus profilometer data were obtained after testing. Experiment Results Following is a discussion of the roller wear test results. The information is organized to aid the discussion. The order of the discussion does not match chronological order of testing. The experimental data to be discussed herein includes the visual appearance of the roller surfaces as testing progressed, amounts of  visible wear debris, the change of mass of rollers both individually and as a pair, and roller surfaces  conditions at start and end of test as revealed by stylus profilometer measurements.  93