In this case it is presumed that the size of the wear scar was very small around 100 μm in diameter, the amount of the lubricating oil was small due to the lubrication method of the application type, and the temperature of the friction surface around 423K necessary for forming the reactive film was partially exceeded. It is thus concluded that the sulfur and phosphor extreme-pressure additive are effective for the steel material, but the extreme-pressure film can not be formed excellently for chromium oxide or molybdenum like the present sample.
3.2.3 Results of Observation of Metallic luster area
As mentioned in 3.2.1 above, the metallic luster area which looked bright looks projected at a glance, and the part which looked dark looks recessed from the results of observation by the optical microscope (Fig. 6). To verify the phenomenon, the depth of the metallic luster area was measured. It is known that the region is formed of molybdenum which is the main phase of the spray coated ceramics from the results of the EPMA analysis in 3.2.2 above. The results of measurement by the fringe scanning laser intervention microscope are shown in Fig. 8(a), and the results of measurement by the mutual focus scanning laser microscope are shown in Fig. 8(b) respectively.
(a)-1 shows the image of the worn surface by the CCD, and the sectional curve of the part A-A is obtained as (a)-2. From this result, it is clear that the bright metallic luster area is deeper than its peripheral parts, and the depth is about 0.2 μm. (b)-1 is the view of the metallic gloss part in the different view from (a)- 1. The depth is about 0.24 μm from the surface profile of the part B-B, supporting the results of measurement by the former. From these findings, the molybdenum phase looking projected at a glance has the characteristic difference compared with the interpretation to be obtained only from the optical microscope possibly due to the peculiarity of the spray coated ceramics.
Fig. 8 Surface observation of luster area (Mo) by different two methods
Considering both results of measurement, it seems that the wear of the molybdenum phase in the spray coated ceramics is selectively advanced. The following three points are considered for this reason. First of all, as the thermal factor, molybdenum was deformed larger by the difference in the coefficient of thermal expansion, secondly, as the mechanical factor, molybdenum which is metal was deformed larger, and thirdly molybdenum low in hardness was selectively worn by the abrasive effect by foreign matters such as free wear debris.
