Embedding behavior of ceramic particles in babbitt coatings and its effect on the tribological properties of low-pressure cold sprayed coatings
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Date
2020-08-07
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Abstract
The low melting point of Sn-based Babbitt alloys often causes nozzle clogging in the
low-pressure cold gas-dynamic spraying (LPCGDS) process, which impacts the process steadiness
and the coating quality. Adding hard particles to the feedstock material eliminates this kind of
interruption. A certain amount of these particles finds their way in the obtained coatings. These
particles also trigger a kind of “hammering effect” due to their impulse forces. These forces are
directly dependent on the mass and velocity of the impacting hard particles. However, these forces
may lead to a decrease in the porosity and improve the adhesion of the obtained coating. In this study,
the effect of the density and size of the hard particle was examined by three different hard materials,
Cr3C2, Al2O3, and B4C, which have a material density of 6.68, 3.95, and 2.52 g/cm3, respectively.
The used feedstock in this study is a powder mixture that contains 75 vol.% Babbitt and 25 vol.% of
either B4C, Cr3C2, or Al2O3. The effect of the size distributions “particles with lower mass” was tested
using two different Al2O3. The various hard particles show different embedding behaviors, as well as
different effects on the coating build-up. It was found that the blended hard particles were enclosed
with the Babbitt matrix, and their interface with Babbitt shows no clear evidence of pronounced
diffusion. The size distribution of the blended hard particles has a direct effect on the splat formation
and the obtained coating microstructure. It was found that the type of hard particles played a decisive
role in the friction behavior. Nevertheless, the hard particle reinforced Sn-Sb-Cu-based composite
coatings demonstrated a nearly constant coeffcient of friction throughout the load-interval.
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Keywords
Low-Pressure Cold Gas-Dynamic Spraying (LPCGDS) process, Sn-based Babbitt coatings, Tribological behavior, Embedding of hard particles, Particle size distribution, Splat formation