It appears a large number of micro-pitting while the
macro-pitting cannot be found under two type of stress
levels of slide-rolling contact process after 5×105
revolutions. The diameter and depth of the micro-pitting
are in micron-grade. The topography measurement of
micro-pitting is performed by NewView 5022 surface
profiler made by U.S. ZYGO Company. The
morphology of pitting when equivalent Hertzian contact
stress are 0.8 GPa and 1.21 GPa after 5×105 revolutions
are showed in Fig.11 and Fig.12, respectively. The
morphology of five micro-pitting are randomly measured
under these two stress levels, respectively. From the
statistical results in Table 1, it can be seen that the shapes
of the most micro-pitting are circular and the angles with
the plane are from 30° to 60°, and the areas are less than
0.005 mm2, the depth are less than 12 μm. Meanwhile, it
can be seen that crack extended along the edge of pitting
(see Fig.12) even one pitting is connected with another
one (see Fig. 12(d)), which cause the irregularity shape
of the surface. The depth of micro-pitting under two
stress levels have no obvious difference and most of
them are less than 15μm. But it will cause material crack
around the pitting and accelerate the expansion of the
pitting under larger normal applied load.
Macro-pitting suddenly appears after 6×105
revolutions. Here, a larger range roughness measuring
instrument SJ-210 which the measuring range can reach
360 μm (-200 μm~+160 μm) are used to measure the
size and topography of macro-pitting. Ten macro-pitting
are randomly selected under equivalent Hertzian contact