Abstract:To protect aluminum parts in vehicle engines, metal-based thermal barrier coatings in the form of Fe 59 Cr 12 Nb 5 B 20 Si 4 amorphous coatings were prepared by high velocity oxygen fuel (HVOF) spraying under two different conditions. The microstructure, thermal transport behavior, and wear behavior of the coatings were characterized simultaneously. As a result, this alloy shows high process robustness during spraying. Both Fe-based coatings present dense, layered structure with porosities below 0.9%. Due to higher amorphous phase content, the coating H-1 exhibits a relatively low thermal conductivity, reaching 2.66 W/(m·K), two times lower than the reference stainless steel coating (5.85 W/(m·K)), indicating a good thermal barrier property. Meanwhile, the thermal diffusivity of amorphous coatings display a limited increase with temperature up to 500 • C, which guarantees a steady and wide usage on aluminum alloy. Furthermore, the amorphous coating shows better wear resistance compared to high carbon martensitic GCr15 steel at different temperatures. The increased temperature accelerating the tribological reaction, leads to the friction coefficient and wear rate of coating increasing at 200 • C and decreasing at 400 • C.
To
improve thermal barrier applications in advanced vehicle engines,
a novel Fe-based amorphous composite coating was designed by introducing
ceramic oxides and was prepared by atmospheric plasma spraying (APS).
The microstructure and related properties of the as-deposited coating
were investigated in detail. The composite coating comprises a well-formed
FeCrNbBSi amorphous metallic matrix and dispersed yttria-stabilized
zirconia (YSZ) splats. A unique Si-oxide interfacial layer with a
thickness of several nanometers and an amorphous structure forms between
the metallic matrix and ceramic phase, which is attributed to a combination
of multiple effects. The composite coating displays extremely low
thermal conductivity from 2.28 W/mK at 100 °C to 3.36 W/mK at
600 °C and can increase the surface temperature of the piston
crown by 18.93 °C, which implies a significant means of enhancing
the power efficiency. The improved thermal barrier ability of the
composite coating is revealed as the crucial effect of the Si-oxide
interfacial layer, which induces an increased interfacial thermal
resistance. The fracture toughness of the composite coating remains
at 3.40 MPa·m1/2, comparable to that of the monolithic
amorphous coating, 3.74 MPa·m1/2, which is closely
related to the formation of a Si-oxide layer and its nanoscale thickness.
Therefore, the Fe-based amorphous composite coating developed here
demonstrates great potential as an innovative metal-based thermal
barrier coating for application in vehicle engines and provides specific
inspiration for future works exploring the interfacial engineering
of coating.
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