The partial contacting was generated with excellent reappearance in the case of the uncoated ceramics. In considering the contact of the actual piston ring with the cylinder liner, the partial contacting is inclined in the sliding direction, realizing the sliding mode where the lubricating oil film is easily formed due to the squeeze effect of the lubricating oil. The present test method provides the inclination in the direction orthogonal to the sliding direction, and it seems that the present method reappears severer partial contacting condition than that in the actual engine.
2.2.2 Effect of Improvement of Initial Surface Break-in Condition by Plating
Fig. 4 and Fig. 5 indicate the results of the partial contacting wear test of the uncoated ceramics and the Ni-P + PTFE plating. In both figures, the results of the measurement of the surface profile of the pin specimen were cut out and attached on the results of the measurement of the surface profile of the disk specimen so that the contact condition of the pin specimen with the disk specimen can be sufficiently checked.
As clarified in the comparison in Figs. 4 and 5, the effect of the plating is not clear in the first test of 1500N x 0.5 Hr, but the wear of the plated specimen is clearly less in the second test of 4500N x 0.5 Hr. In addition, in the third test of 4500N x 20 Hr, the disk specimen to the plated pin specimen is little worn while the disk specimen to the uncoated pin specimen is already worn by not less than 60 μm, and roughness of the surface profile is large.
Fig. 4 Surface profile after wear test (Uncoated ceramics)
Fig. 5(b) shows a part not in contact with the disk specimen at the center part of the pin specimen, and it is understood from the result of surface observation that this is the separated Ni-P + PTFE plating.
The material to carry the load is different at the boundary of the separated part in the center. That means, the spray coated ceramics of the base material is exposed on the left side of the separated part where the partial contacting is severer and brought into direct contact with the disk specimen while the plating is left on the right side.
In Fig. 5(c), no remarkable effect of separation is seen in the plating, and it seems that the plating is completely diminished by the wear, and the initial break-in condition is excellently advanced. It is thus considered that the plating of relatively low hardness shares a part of the load even under the partial high bearing pressure such as the partial contacting, and the excellent initial break-in condition is obtained through the gradual wear while preventing reaching the bearing pressure under which the hard spray coated ceramics generates abnormal wear.
Fig. 5 Surface profile after wear test (Ni-P+PTFE coated ceramics)
