Elsevier

Wear

Volumes 462–463, 15 December 2020, 203514
Wear

Simple synthesis of the composite coating and the lubrication mechanisms of the spherical SnAgCu–Al2O3

https://doi.org/10.1016/j.wear.2020.203514Get rights and content

Highlights

  • Flame spray welding is used to prepare spherical SnAgCu–Al2O3 (S-SA).

  • Serrated structure is used to enhance bonding strength of coating and Ti-alloy.

  • The composite coating is fabricated using spark plasma sintering.

  • At 235 °C, friction coefficient and wear rate of a Ti–S-(SA) are lowest.

  • At 235 °C, the spherical SnAgCu film occurs excellent flowing for good lubrication.

Abstract

Tribological behavior of coatings plays a crucial role in increasing the service life of aerospace components and biological devices. In this study, spherical SnAgCu–Al2O3 (S-(SA)) and Ti–S-(SA) coatings were prepared. Herein, using a ball-on-flat tribometer, the optimal tribological property of the Ti–S-(SA) was obtained at a load of 16 N. The SnAgCu-enriched film achieved good deformation during wear and induced the rolling of spherical Al2O3, which resulted in excellent lubrication. The friction and wear behaviors of the Ti–S-(SA) coatings were further optimized at a temperature (235 °C) close to the melting point of SnAgCu (240 °C). This resulted in excellent flow of SnAgCu, which, in turn, enhanced the rolling friction with the Al2O3, thus furnishing better lubrication. We believe that this study will be beneficial for enhancing the tribological characteristics of coatings and determining the possible solutions for commercial applications.

Introduction

In recent years, titanium alloys have attracted significant research interest owing to their improved performance under friction and wear and their tribological applications [1,2]. The tribological behavior of Ti alloys, especially under dry sliding wear, plays an important role in increasing the service life of aerospace component and biological device [3,4]. However, during device fabrication process, conventional Ti alloys generally display poor friction and wear behaviors, which result in unsatisfactory service life [[5], [6], [7]].

For enhancing tribological properties, CuAg [8], CuSn [9], and SnAgCu [[10], [11], [12]] have been proposed as potential lubricants for preparing self-lubricating composites. Hu et al. [8] and Kumar et al. [9] investigated the effect of CuAg and CuSn migration, respectively, on the tribological behaviors of Ti alloy. The result suggested that the migration of CuAg and CuSn can induce the formation of a lubricant interface, which resulted in poor friction and wear behaviors. However, the low melting point of the composites limited their applications at temperatures above 450 °C. Furthermore, studies have reported that friction and wear behaviors of SnAgCu composite degraded at higher temperatures [10,11]. However, SnAgCu was bonded strongly with its substrate, thereby restricting the migration and curtailing a reduction in the friction coefficients and wear rates. To accelerate the SnAgCu migration, Liu et al. [12] prepared self-lubricating composites using M50 materials and filled their surface micropores with SnAgCu. The result proved that the migration of SnAgCu toward the frictional interface accelerated, thereby facilitating the formation of a SnAgCu-rich interface. In another study, the synergetic cooperation between fullerene and SnAgCu was attempted, which enhanced the friction and wear behaviors at elevated loads [13]. However, the high oxidation temperature of the fullerene limited the cooperative lubrication at low temperatures. Furthermore, the load capacity of porous composite was compromised, which resulted in surface microcracks and cross-sectional fractures at high loads.

Higher load capacity could be achieved by coating the surface with composites, rather than filling a porous material, because the coating yielded excellent mechanical properties. Ying et al. [14] found that the addition of CuSn into the coating conferred excellent wear resistance to the composites. The effects of Al2O3 particles on the tribological behavior of coatings were also investigated [[15], [16], [17]], where the particles were presented on the frictional interface, thereby improving the anti-friction and anti-wear behavior of the coating. However, the high resistance of substrate material to the incorporation of Al2O3 limited the migration of Al2O3 from the composite, which resulted in insufficient enrichment and limited the lubrication ability. Sadoun et al. [18] exploited the cooperative effects of Cu and Al2O3 particles for reducing the bonding strength between these species. However, insufficient enhancement in the properties of Cu–Al2O3 than those of the as-prepared Al2O3 was observed. Recently, it was found that the thermal expansion of coating differed significantly from that of the substrate, thereby resulting in their separation and lubrication failure. This remains a major challenge in the design and preparation of lubricant coatings.

In few studies, for reducing the bonding strength of the Al2O3 and improving the lubrication of SnAgCu, the Al2O3 particles were wrapped with SnAgCu to generate spherical SnAgCu–Al2O3 (S-(SA)) via flame spray welding. For preparing the S-(SA) coating, spark plasma sintering was used to prepare the coating on commercial Ti alloys. A serrated microstructure was lasered into the Ti alloy surface for increasing the binding force of the coating to the substrate. However, the tribological behavior of the coating based on the cooperative mechanism involving SnAgCu and Al2O3 has not been analyzed.

In this study, we investigated the friction and wear behaviors of SnAgCu, Al2O3, SnAgCu–Al2O3 (SA), and S-(SA) coatings. In the first step, S-(SA) was prepared by flame spray welding. In the second step, a serrated microstructure was embedded into the Ti alloy surfaces using laser sculpting. In the third step, coatings were synthesized using spark plasma sintering (SPS). In the fourth step, the friction and wear behaviors of the coatings were examined. Finally, the lubrication properties of SnAgCu, Al2O3, SA, and S-(SA) were analyzed under varying loads and temperatures. Subsequently, the surface morphology, elemental distribution, and three-dimensional texture of the coatings were characterized in detail using electron probe microanalysis (EPMA), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The results obtained herein provide useful data for increasing the service life of aerospace components and biological devices.

Section snippets

Synthesis of spherical SnAgCu–Al2O3

SnAgCu and Al2O3 powders with nominal mass ratios of 68.44 and 31.56 wt% were used to prepare the spherical S-(SA). Herein, SnAgCu comprised 92.55 wt% Sn, 3.88 wt% Ag, and 3.57 wt% Cu, which have been shown in Table 1. The powders, with particle diameters ranging from 20 to 85 μm, were mechanically mixed in a vibration mixer for 80 min at a frequency of 45 Hz. The mixture was utilized to prepare S-(SA) by flame spray welding. Under Ar atmosphere, the mixture was transferred to a nozzle at a

Analysis of friction and wear behaviors under loads

Fig. 9 shows the typical wear rates and friction coefficients of the Ti-A, Ti–S, Ti-SA, and Ti–S-(SA) coatings under different loads, when slid against the Si3N4 spheres. As shown in Fig. 9a and b, Al2O3, SnAgCu, SA, and S-(SA) were added into the coatings, and they demonstrated better resistance to friction and wear than the uncoated Ti alloy. Notably, the Ti–S-(SA) coating displayed the greater resistance to friction and wear than the Ti-A, Ti–S, and Ti-SA coatings. At a load of 16 N, a

Conclusions

This study mainly focused on the simple synthesis and lubrication mechanisms of composite coatings, and the conclusions are as follows:

  • 1)

    The S-(SA) and Ti–S-(SA) coatings can be successfully prepared by combining flame spray welding and SPS.

  • 2)

    At a load of 16 N, the friction coefficient of ~0.27 and wear rate of ~2.94 × 10−4 mm3 N−1 m−1 were observed in the Ti–S-(SA), which were smaller than the friction coefficients (0.30–0.35) and wear rates (3.22–3.92 × 10−4 mm3 N−1 m−1) of the Ti–S, Ti–S, and

Prime novelty statement

Please provide a Prime Novelty Statement for your manuscript below. This statement should provide information as to what is new and novel in the manuscript, and is provided to referees for consideration when reviewing manuscripts.

Preparation novelties: The flame spray welding is firstly used to prepare spherical SnAgCu–Al2O3 (S-SA), that makes the Al2O3 particles be well coated using massive SnAgCu. The serrated microstructures, which are fabricated by the laser sculpture, are firstly used to

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work is supported by China postdoctoral Science Foundation (2019M662484), Henan postdoctoral Foundation and postdoctoral Foundation of Anyang Institute of Technology (BHJ2019006), Funding of Henan Educational Committee (19A460011), Doctoral Start-up Funding of Anyang Institute of Technology (BSJ2018005), Project for Science and Technology Plan of Henan Province (192102210010), Tribology Science Fund of State Key Laboratory of Tribology (SKLTKF18B09), Sichuan Provincial Key Lab of Process

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