Embedding Behavior of Ceramic Particles in Babbitt Coatings and Its Effect on the Tribological Properties of Low-Pressure Cold Sprayed Coatings

Wolfgang Tillmann,Mohamed Abdulgader,Leif Hagen,Steffen Hüning

doi:10.3390/coatings10080769

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 coefficient of friction throughout the load-interval.

Highlights

IntroductionMetal deposition processes are mostly referred to as thermal spraying processes, which make use of the combination of thermal and kinetic energies to heat-up feedstock materials (metals or composite of metals and metal–ceramics) and accelerate them towards a prepared substrate surface
Metal deposition processes are mostly referred to as thermal spraying processes, which make use of the combination of thermal and kinetic energies to heat-up feedstock materials and accelerate them towards a prepared substrate surface
Chromium(II) carbide has among all other hard particles the highest density of 6.68 g/cm3 compared with 3.94 g/cm3 in the case of aluminum oxide, and 2.51 g/cm3 for boron carbide

Summary

Introduction

Metal deposition processes are mostly referred to as thermal spraying processes, which make use of the combination of thermal and kinetic energies to heat-up feedstock materials (metals or composite of metals and metal–ceramics) and accelerate them towards a prepared substrate surface. The ratio between thermal and kinetic energies in the thermal spraying processes determines the impulse (linear momentum) of the impacting particles, and their spreading behavior upon the prepared substrate surface. Changing the mass of the inflight particles by either changing their density or size will affect their impulse forces directly. Another way of changing the impulse forces of the in-flight particles upon impacting is to change their temperature, which changes the density of the in-flight particles, and if the temperature high enough, even their state of matter.

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