Volumen II - SAM

[9-10] which is characterized by the transfer of soft polymeric material to the counterface [11]). We therefore
conclude that MoS2 reduces wear rate because it inhibits surface melting (by increasing the thermal
conductivity of composites and therefore enhancing heat dissipation) and improves the ability of PE to
produce a uniform and adherent transfer film (by means of an adhesive wear mechanism).
SEM of abrades surfaces under abrasive conditions exhibited similar features (figure 4). PE abraded surface
appears wrinkly probably due to severe surface melting. The rubbing surfaces of PE/07, PE/10 and PE/20
composites are less coarse than the one of PE, maintaining the flowing track parallel to the sliding direction.
Wear debris appears in the form of large slices. PE/10 composite shows little and mild deformation. When
the amount of MoS2 is large (PE/25), besides micro-plugging and micro-cutting features, evidences of microcracking
appear as well.
Figure 4. SEM of composite’s abraded surfaces under abrasive wear.
Previous explanation is not suitable under abrasive conditions, where the transfer film has not chance to
form. SEM+EPMA analysis performed over original and abraded surfaces reveals that while in original
surface there were Mo, S (from MoS2) and C (from PE), in abraded surface Mo and S are absent (figure 5). It
seems that MoS2 was liberated during abrasion test. Remembering TOM results (Figure 1), this wear
mechanism appears possible. We therefore believe that during abrasive wear MoS2 particles are ploughed out
together with matrix material, playing a role as a rolling third body between the abrasive surface and the
polymer composite, thus reducing shear stress, friction coefficient and contact temperature [12].
Figure 5. SEM+EPMA elemental analysis of abraded surface of PE/10 composite.
Appearance of fracture surfaces of PE/10, as seen by SEM, is completely different from that of PE (Figure
6). Plastic deformation is clearly seen in PE fracture surface. Evidences of brittle fracture and matrix-filler
de-bonding are noticed in PE/10 fracture surface. Only little plastic deformation is seen for this composite
under quasi-static conditions.
To understand mechanical behavior reader should keep in mind BES + EPMA results which revealed the
lack of physical continuity of HMW-HDPE matrix (Figure 2). This morphology seems to have a deleterious
effect on the mechanical behavior of composites. TOM analysis of PE/10 before fracture suggests that cracks
can easily run trough MoS2 rich phase (Figure 7). BES + EPMA analysis of fracture surface gives extra
evidence to this assumption. BES shows that fracture surface consist of bright bumps, compatible with
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