/g38/g82/g81/g73/g76/g74/g88/g85/g68/g87/g76/g82/g81/g3/g24/g3/g177/g3/g53/g72/g86/g88/g79/g87/g86 : The fifth configuration for discussion is the upper roller material hardened and  passivated 440C steel. The lower roller was Ti6Al4V material treated by plasma electrolytic oxidation (PEO). The vendor of the PEO process also chose to apply on top of the PEO treated surface a bonded solid lubricant film, a combination that in their experience performed well. The configuration was put to test with the philosophy that failure of the bonded film need not define the capability of the PEO surface itself. One 93,000 cycle test was completed. The blue-colored solid lubricant film wore away and created a mixture of powder and large flakes of debris. The blue-colored bonded film transferred onto the upper steel roller during the early part of the testing, but later this transferred film was almost completely removed from the upper roller [Figure 6(e)]. There was significant adhesive wear. The final condition of  the rollers for this configuration appeared visually similar to that of Configuration 2. The net mass lost  from the upper 440C roller was 0.002 gram, also similar to the result of Configuration 2. Given the result of this test and given the lack of experience using the PEO process for space mechanisms, it was decided not to further pursue evaluations of PEO-treated Ti6Al4V for this application.  /g38/g82/g81/g73/g76/g74/g88/g85/g68/g87/g76/g82/g81/g3/g25/g3/g177/g3/g53/g72/g86/g88/g79/g87/g86/g29 The sixth configuration for discussion is the upper roller material hardened and  passivated 440C steel and the lower roller material Ti6Al4V with a PVD-applied coating of a (WC)aC:H  diamond-like-carbon (DLC) composition. One test was completed to 91,000 cycles. In this test configuration the problematic Ti6Al4V alloy was coated with a galling-resistant composition hoping to defeat the adhesive wear mechanism. However, for these particular contact conditions wear occurred to  both rollers throughout the course of the test. As the wear occurred a significant amount of debris was  noted on the debris tray. During the first 25 percent of the test duration, the rollers surfaces appeared to  have relatively low surface roughness suggestive of abrasive wear. By the end of the test the rollers surfaces conditions suggested the process had become primarily adhesive wear [Figure 6(f)]. Profilometer inspections of the rollers confirmed that the wear behavior of this configuration was different  from the other configurations. The lower Ti6Al4V roller had a prominent wear valley with roughness  features within the wear region, and by mass measurements the lower roller net mass lost was 0.007 gram. This was the only configuration were the majority of mass loss was only from the lower Ti6Al4V roller. This configuration is not suited for the present application. /g38/g82/g81/g73/g76/g74/g88/g85/g68/g87/g76/g82/g81/g3 /g26/g3 /g177/g3 /g53/g72/g86/g88/g79/g87/g86 : The seventh configuration for discussion is the upper roller material of  hardened 440C steel and the lower roller Ti6Al4V. The surfaces of both rollers were coated with a  (TiC)aC:H DLC composition applied by PVD. One test was completed to 96,000 cycles. The wear progression had some similarities to the test of configuration 6. Wear occurred to both rollers throughout the course of the test. As the wear occurred, a significant amount of debris was noted on the debris tray. Early in the test the wear may have been abrasive wear, but as the test progressed the surface  roughness features became more apparent and end of test conditions suggested adhesive wear [Figure 6(g)]. Profilometer inspections of the rollers at the end of test show differing behaviors for  Configuration 6 (lower roller only coated) compared to Configuration 7 (both rollers coated). The (Wc)aC:H coated lower roller of configuration 6 that was mated to an uncoated upper roller had no peak  features and one prominent wear valley. On the other hand, for configuration 7 with (Tic)aC:H coating on  both rollers, the lower roller had both peak and valley features. The upper rollers for Configurations 6 and 7 have similar surface profiles at the end of the test having a combination of peak and valley features of about 5 micrometer size. The use of the DLC coatings changed the wear behavior compared to tests  without any coatings or solid-film lubrication. While DLC coatings may have a place for space mechanisms with more optimization and research, further consideration and testing of DLC coatings was  not pursued for this application. /g38/g82/g81/g73/g76/g74/g88/g85/g68/g87/g76/g82/g81/g3/g27/g3/g177/g3/g53/g72/g86/g88/g79/g87/g86/g29 The eighth configuration for discussion is the upper roller material hardened  440C steel and the lower roller anodized Ti6Al4V. The upper roller only was provided a MoS 2 nanocomposite coating by PVD sputtering. Four tests were completed using this configuration. The steel  upper rollers with the sputtered coatings were passivated prior to coating except for one test the roller was not passivated because of testing schedule. The lack of passivation for one test probably did not have a big influence on performance, as the rollers are processed by a high-energy ion beam just prior to  sputtering. The ion beam likely removes most or all of the oxides created during passivation. The test  96