433 that, when new, had a circular crown. As this roller loses material the wear track widens. The worn 440C  roller appears slightly smoother than the 440F roller suggesting that steel wear debris would in general be smaller for the case of 440C compared to 440F. Recall that the 440F is alloyed to be “free machining” and to thereby produce chips more easily and of greater length during machining. The last row of Figure 8 shows dramatically reduced wear when the rollers are exactly aligned (final row of Figure 8). Even after significantly longer running time the aligned rollers appear almost like the running-in condition (first few hundred cycles) of the misaligned rollers. Still, for the aligned condition one can notice in the very center of the wear track a narrow band that exhibits adhesive wear. 

Table 1.  Summary of Test Conditions     

To study the wear, rollers were inspected using a scanning electron microscope (SEM). By using x-ray photoelectron spectroscopy the constituents of particular regions of the rollers could be investigated. In all cases, two-way transfer of material was observed. That is, titanium alloy substrate was found on the 440 steel rollers and steel alloy was found adhered to the titanium alloy rollers. An example from inspection of the titanium alloy roller from test ID 3 of Table 1 is provided in Figure 9. An overall view of a region near the center of the wear track is given in Fig 9(a), and also noted are regions where spectroscopy was assessed. The bright regions noted as #1 and #2 in Fig. 9(a) produced the respective spectra of Fig. 9(b-c). Here in the spectra of Fig. 11(b-c) we note the clear presence of iron, chromium, and alloying elements of the 440 steel. Region #2 had a brighter appearance suggesting a more complete coverage of the substrate, and the spectrum for region #2, Fig. 9(c), has a very strong peak correlating to iron. The darker region noted as numeral 3 in Fig. 9(a) produced the spectrum of Fig. 9(d). Here the titanium is still exposed, we observe peaks correlating to titanium and aluminum, and peaks correlating to iron and chromium are not present. The spectrum for the region marked with the numeral 4 in Fig. 9(a) is not shown here but was consistent with that of Fig. 9(d). These trends were true for all of many samples inspected. In all cases the worn regions included regions of the base material still exposed and also contained adhered material from the mating roller. As will be noted, in net, mass was lost for the 440 steel rollers. However, in all cases Ti6Al4V material was found on the tested steel rollers via SEM spectroscopy. 

  test # roller pair test ID material outer surface  conditionmaterial outer  surface  conditionspeed  (rpm)misalignment  angle (deg) 1 1 1 440C bare Ti6Al4V bare 15 -1.4 2 2 2 440F bare Ti6Al4V bare 15 -1.43 3 3 440F bare Ti6Al4V anodized 15 -1.44 4 4 440F bare Ti6Al4V anodized 15 0.05 5 5 440F passivated Ti6Al4V anodized 9 -1.46 6 6 440F passivated Ti6Al4V anodized 15 -0.4 7 7 7 440F passivated Ti6Al4V anodized 15 -0.9 8 8 8(a) 440F passivated Ti6Al4V anodized 15 0.09 8 8(b) 440F passivated Ti6Al4V anodized 15 -0.1 10 8 8(c) 440F passivated Ti6Al4V anodized 15 -0.211 8 8(d) 440F passivated Ti6Al4V anodized 15 -0.312 8 8(e) 440F passivated Ti6Al4V anodized 15 -0.7 13 9 9 440C bare Ti6Al4V anodized 15 -1.5 14 10 10 440C bare Ti6Al4V anodized 15 -1.415 11 11 440C passivated Ti6Al4V anodized 15 -0.9upper roller lower roller test conditions