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In this paper, the comparision of tribological
properties such as wear and cavitation erosion resistance
of High Velocity Oxy Fuel (HVOF)
sprayed coatings onto AZ31 magnesium alloy
were examined. As a coating material, three commercially
available powders: WC-Co-Cr, WCCo
and WC-Cr3C2-Ni were used. The manufactured
coatings were analyzed extensively using
optical microscopy (OM), X - ray diffraction
(XRD) and scanning electron microscopy
(SEM), respectively. In the case of mechanical
properties, the hardness, microhardness, elastic
modulus and fracture toughness were measured.
Cavitation erosion tests were conducted according
to ASTM G32 with the stationary specimen
method. Dry sliding wear tests were conducted
using WC counter sample according to ASTM
standard. In both tests, the results were compared
with the AZ31 magnesium references sample.
Cavitation tests indicate that in the initial stages
of erosion the WC-Co-Cr sample has slightly
higher resistance than WC-Cr3C2-Ni and far better
cavitation resistance than WC-Co coatings. In
further stages of erosion, the Ni-containing coating
delaminates due to its lower fracture resistance
and WC-Co-Cr sample stays solid until
the end of test time. As-sprayed samples exhibit
accelerated mass loss. The main wear mechanism
resiles on the detachment of cermet material
starting at microstructural and surface nonuniformities
such as pores and ceramic-metallic
phase interfaces. In the case of sliding wear, the
results are strongly related to the mechanical
properties. The WC-Co and WC-Co-Cr samples
hardness, Young modulus exceed the WC-Cr3C2-
Ni, therefore, presents lower values of wear factor,
on the level of approximately 6·10-7
mm3/N·m and coefficient of friction related to
0.4. The wear mechanism is affected by abrasion,
growing and transfer of the material between
counterball and coatings. Deposition of the cermet
coatings effectively prevents the magnesium
substrate which is presented very poor resistance
to cavitation and sliding wear.
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