Microstructural Characteristics in Babbitt Coatings Deposited by LPCS

Wolfgang Tillmann,Michael Paulus,Mohamed Abdulgader,Leif Hagen,Mark Dennis Kensy

doi:10.3390/coatings10070689

Abstract

Studies have already established that the mechanical properties of Babbitt coatings significantly depend on the microstructural characteristics, such as the amount and distribution of intermetallic compounds dispersed in a soft solid solution matrix. For Sn–Sb–Cu-based Babbitt coatings, the formation of SbSn- and CuSn-based precipitates has a substantial influence on the resulting microhardness and thus determines the maximum load carrying capacity. Thermal spraying of Sn-based Babbitt coatings results in a relatively more refined structure of these precipitates than in common manufacturing processes, such as casting, due to the thermal processing conditions. This study aims to evaluate the effect of the temperature of the propellant gas and substrate temperature on the microstructural characteristics of Sn–Sb–Cu-based Babbitt coatings deposited by low pressure cold spraying (LPCS). The deposits were examined for their phase composition, microhardness and mesoscopic structure. It was found that the coatings were mainly composed of Sb2Sn23, Sb0.49Sn0.51 and Sorosite (CuSn or CuSb0.115Sn0.835), regardless of the substrate temperature or temperature of the propellant gas to be investigated. For a gas temperature above 300 °C, an increased microhardness was observed, which correlates with the appearance of a more homogenous distribution of Sb0.49Sn0.51 dispersed in a soft Sn-rich solid solution matrix.

Highlights

Sn-based alloys, known as Babbitt or white metal, represent a group of alloys that contains different grades of Sn with the addition of Cu and Sb
(i.e., room temperature), it was found that the produced Sn–Sb–Cu-based coatings exhibited a high amount of porous zones, which predominantly occurred next to the coating–substrate interface (Figure 2a–c)
For an substrate temperature (ST) of 260 ◦ C, the coatings were deposited by using a PGT of 300, 350 and 400 ◦ C

Summary

Introduction

Sn-based alloys, known as Babbitt or white metal, represent a group of alloys that contains different grades of Sn with the addition of Cu and Sb. Sn–Sb–Cu-based Babbitt alloys mainly consist of a soft solid solution matrix interstratified with intermetallic phases, such as SnSb and Cu6 Sn5 [1]. The formation of Cu6 Sn5 or Cu3 Sn in part results from the interaction of Cu with liquid Sn. Cu3 Sn usually arises from the formation of Cu6 Sn5 [2], wherein the formation of Cu3 Sn necessitates an increased Cu content and higher temperatures. For common Cu contents, the formation of Cu3 Sn is less likely. The hexagonal phase can be stabilized with the addition of further elements [4]. The inclusion of small amounts of Sb leads to the formation of Cu6 Sn5−x Sbx and shifts the region of thermal stability from 186 ◦ C down to room temperature

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