Abstract
Sn-based Babbitt coatings are widely used for sliding in hydrodynamic bearings. The Babbitting of bearing surfaces is among others accomplished by casting; however, this implies some disadvantages such as segregations, or susceptibility to shrinkage defects. Thermal spraying represents a promising method to overcome these challenges. To date, no studies on Babbitt coatings deposited by means of low-pressure cold spraying (LPCS) are available in the literature. In this study, a first attempt is made to produce a Sn-Sb-Cu-based composite coating reinforced with alumina particles by means of LPCS which enables the coating of internal diameters (IDs) of cylindrical components. A tailor-made feedstock was utilized which consists of a powder mixture of Sn, Sb, Cu and alumina. The composite coating is investigated with regard to its microstructural and tribological characteristics using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), x-ray diffraction (XRD), as well as dry sliding experiments. Metallographic investigations demonstrate the feasibility of depositing an alumina-reinforced Sn-Sb-Cu-based composite coating with a dense microstructure and low porosity. The composite coating mainly consists of Sn, SbSn, Cu and hexagonal CuSn. Despite a small fraction of alumina particles, the microhardness of the composite coating is primarily determined by the formation of SbSn intermetallic phases dispersed in the soft Sn-Sb-rich matrix. The composite coating possesses a coefficient of friction of 0.43 ± 0.01 and wear coefficient k of 17.27 ± 7.77 × 10−5 mm3 N m−1 sliding against a 100Cr6 counterbody.
Highlights
Babbitt, called white metal, represents a group of alloys that contain different grades based on Sn or Pb, with the addition of Cu and Sb
A first attempt is made to produce a Sn-Sb-Cu-based composite coating reinforced with alumina particles by means of low-pressure cold spraying (LPCS) which enables the coating of internal diameters (IDs) of cylindrical components
When compared to common Babbitt coatings, the findings within this study indicate that the coefficient of friction (COF) of the aluminareinforced Sn-Sb-Cu-based composite coating produced by LPCS is found to be higher than the COF of Babbitt coatings (i.e., ASTM B23 grade 2) deposited by conventional casting, but slightly lower than the COF as reported for arc and flame sprayed Babbitt coatings (Ref 20)
Summary
Called white metal, represents a group of alloys that contain different grades based on Sn or Pb, with the addition of Cu and Sb. Junior et al (Ref 20) recently investigated the microstructural and tribological characteristics of Babbitt coatings (ASTM B23 grade 2) deposited by arc spraying and flame spraying and compared the findings with those obtained from coatings deposited by centrifugal and conventional casting processes. The authors clarified that the thermally sprayed Babbitt coatings exhibit, despite a higher porosity, an enhanced wear resistance in dry sliding experiments compared to the conventional Babbitt surfaces. The authors stated that the superior wear resistance is attributed to the fact that the precipitates formed in the thermally sprayed Babbitt coatings are more refined than those observed in deposits produced by common processes. Sn-Sb-Cu-based feedstocks are widely available, to date no studies on Babbitt coatings deposited by means of LPCS are available in the literature The absence of such studies currently does not allow a comparison between the coating properties of conventional Babbitt coatings and low-pressure cold gas-sprayed Babbitt coatings. The findings are compared and discussed with those reported for Sn-Sb-Cu-based coatings, i.e., Babbitt coatings, deposited by arc and flame spraying as well as conventional manufacturing techniques such as casting
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