Microstructure and tribological behavior of tungsten inert gas welding arc brazing tin-based babbit
来源期刊:Rare Metals2020年第2期
论文作者:Fang-Ming Zhou Qing-Ya Zhang Ming-Xiao Shi Hui Li Jun-Wu Guo
文章页码:193 - 199
摘 要:The microstructure of the tin-based babbit obtained by the method of tungsten inert gas welding(TIG)arc brazing was studied by optical microscopy(OM) and X-ray diffraction(XRD).Tribological behavior was investigated by high-temperature friction and wear testing machine(HTFWT),laser scanning confocal microscopy(LSCM),scanning electron microscopy(SEM) and energydispersive spectrometer(EDS).It can be found that the higher welding current of the melting tin-based babbit makes it possible to form isomer structure with fine crystals of the cubic SnSb compounds and large star Cu6Sn5 compounds so that a higher hardness can be achieved,and a lower wear rate can be obtained over the entire distance of sliding friction.When the applied load is 2 N,the contact surface is oxidized due to the accumulation of friction heat and oxide,which plays a role of lubricated film.Also,the softer Sn-based solid solution forms obvious furrow under abrasive wear,and the harder SbSn and Cu6Sn5 intermetallic compounds shatter and leave a hole under friction.
稀有金属(英文版) 2020,39(02),193-199
Fang-Ming Zhou Qing-Ya Zhang Ming-Xiao Shi Hui Li Jun-Wu Guo
Jiangsu Province Key Laboratory of Advanced Welding Technology,Jiangsu University of Science and Technology
作者简介:*Fang-Ming Zhou,e-mail:fangmingzhou@just.edu.cn;
收稿日期:24 September 2016
基金:financially supported by the University Natural Science Research Project of Jiangsu Province (No. 15KJA460006);
Fang-Ming Zhou Qing-Ya Zhang Ming-Xiao Shi Hui Li Jun-Wu Guo
Jiangsu Province Key Laboratory of Advanced Welding Technology,Jiangsu University of Science and Technology
Abstract:
The microstructure of the tin-based babbit obtained by the method of tungsten inert gas welding(TIG)arc brazing was studied by optical microscopy(OM) and X-ray diffraction(XRD).Tribological behavior was investigated by high-temperature friction and wear testing machine(HTFWT),laser scanning confocal microscopy(LSCM),scanning electron microscopy(SEM) and energydispersive spectrometer(EDS).It can be found that the higher welding current of the melting tin-based babbit makes it possible to form isomer structure with fine crystals of the cubic SnSb compounds and large star Cu6Sn5 compounds so that a higher hardness can be achieved,and a lower wear rate can be obtained over the entire distance of sliding friction.When the applied load is 2 N,the contact surface is oxidized due to the accumulation of friction heat and oxide,which plays a role of lubricated film.Also,the softer Sn-based solid solution forms obvious furrow under abrasive wear,and the harder SbSn and Cu6Sn5 intermetallic compounds shatter and leave a hole under friction.
Keyword:
Tin-based babbit; TIG arc brazing; Microstructure; Tribological behavior;
Received: 24 September 2016
1 Introduction
With the rapid development of manufacturing industry,ships,vehicles,aerospace and other heavy machinery industries have witnessed higher requirements for the antifriction layers of sliding bearing.Babbit alloys (also called white alloys) are one of the various anti-friction materials
Iron substrate and babbit alloys are not compatible metals because of their different melting points (1538℃for Fe and 230℃for tin-based babbit).Casting is a traditional technology applied for bonding babbit alloys to iron substrate,but there are many drawbacks such as pore,peeling and cracking,and a certain thickness layer must be removed by machining,which raises the manufacturing cost and wastes resources
In this study,a kind of tin-based babbit wire was applied to prepare the babbit layers through TIG arc brazing at different welding heating inputs.The aim of this study is to research the effect of welding heating input on the micro structure and tribological properties of tin-based babbit.And it will have certain theoretical and practical significance.
2 Experimental
The tin-based babbit wire with the diameter of 4 mm and Q235B steel with the thickness of 8 mm were used for the study,and their chemical composition is listed in Tables 1and 2.And the argon with the concentration of 99%was used as the shielding gas.Besides,the steel substrate was cut into the size of 50 mm×50 mm,and the surface of which was cleaned before TIG arc brazing.The substrate was fixed,and welding schematic diagram is shown in Fig.1.The welding parameters are listed in Table 3.
Table 1 Chemical constitution of ZChSnSbl1-6 (wt%)
Table 2 Chemical constitution of Q235B (wt%)
Fig.1 Schematic of babbitt metal arc surfacing
Table 3 Welding parameters of TIG arc brazing
The thickness of the tin-based babbit layer is 4 mm,and2-mm-thickness layer would be removed by line cutting.The weld seams were cut into the size of15 mm×15 mm×10 mm,which was used as samples.The cross section of samples was pre-grinded and then polished.And then,they were corroded by 3%-5%nitric acid alcohol corrosion.The microhardness was carried out by MH-5 microhardness tester with the applied load of0.25 N and dwelling time of 10 s.
The friction and wear tests were carried out under the dry friction.Wear rate is based on the formula:I=ΔV/ΔtF,where I is wear rate,ΔV is volume wear loss,At is time and F is load.The specimens with a friction radius of4 mm run in high-temperature friction and wear testing machine (HTFWT).The friction ball was made from GCr15 with the diameter of 3 mm,and its chemical composition is listed in Table 4.Different loads and speeds were used for the friction and wear experiment.The experimental time was 15 min,and experimental temperature was 25℃.The samples were fixed by four screws,and a friction ball was fixed in a bar,and friction and wear diagram are shown in Fig.2.
Micros truc ture of the tin-based babbit was studied by optical microscope (OM,Axioskop 2 MAT) and X-ray diffractometer (XRD,XRD-6000).The wear mechanism and morphology were analyzed through laser scanning confocal microscope (LSCM,LEXT OLS4000) and scanning electron microscope (SEM,JSM-6480) equipped with energy-dispersive spectrometer (EDS).
Fig.2 Friction and wear schematic diagram
Table 4 Chemical composition of GCr15 (wt%)
3 Results and discussion
3.1 Microstructure of tin-based babbit layers
It is well known that the tribological property of tin-based babbit is determined by microstructure characteristics.XRD was used to identify the phase types of tin-based babbit,and the results are shown in Fig.3.It can be seen that the tin-based babbit obtained by the parameters above is composed of three kinds of phases:αphase (copper and antimony solution in Sn matrix),βphase (SnSb compound)andεphase (Cu6Sn5 compound)
Fig.3 XRD analysis of tin-based babbit with different welding currents
The effect of welding current on the microstructure of tin-based babbit is shown in Figs.4 and 5.It can be seen from Fig.4a-c that the straight interface can be obtained when the welding current is<90 A,as shown in Fig.4a,b.While the welding current is 90 A,steel substrate is melted and obvious penetration forms,as shown in Fig.4c.
The microstructural characteristics of tin-based babbit are controlled by the arc brazing current,and the higher welding current can make the melted babbit crystallized form isomer structure of SbSn and Cu6Sn5.As shown in Fig.4d-f,the SbSn cubics are clearly identified in Sn matrix,and the Cu6Sn5 intermetallic compounds that are distributed in Sn matrix have characteristic star shapes that can be easily identified.However,the size of SbSn is fined and the size of Cu6Sn5 is larger as the welding current increases from 50 to 90 A.As shown in Fig.5,with the welding current increasing,the grain size of SbSn decreases from 47.8 to 37.7μm.It is analyzed that since the solidification temperatures of Cu6Sn5-,SbSn-and Sn-based solid solution are 375,273
Fig.4 OM images of babbit layers at different welding currents:a,d 50 A,b,e 70 A and c,f 90 A
Fig.5 Grain size of SbSn compounds
Fig.6 Microhardness of samples and phases at different currents
The tribological property of the tin-based babbit is also associated with the microhardness.Figure 6 shows the microhardness of each sample,αphase,βphase andεphase.It can be seen that microhardness of each sample andαphase is basically constant,while the microhardness ofβphase andεphase increases with the welding current increasing.It is analyzed that the higher welding current makes the isomer structure of SbSn be fined and uniformly distributed Cu6Sn5,which improve the microhardness of SbSn and Cu6Sn5,and the tin-based babbit is overheated when the welding current is 90 A,which also increases the microhardness of SbSn and Cu6Sn5.
3.2 Friction and wear behavior of tin-based babbit surfaces
Tribological property tests were carried out for the tinbased babbit layers,and the experimental results are shown in Fig.7.It can be seen that the friction coefficient is approximately constant for sliding time over 1 min,and this constant value increases with the current increasing.Friction coefficient of the tin-based babbit is directly depended on the roughness of the sample's surface.At the initial stage of friction and wear,the relative roughness of the sample's surface is so large that the friction coefficient changes apparently.
Figure 7b shows the friction coefficient of sample at welding current of 70 A under loads of 2 N and rotation of300 r·min-1.It can be seen that friction coefficient is bigger and changes more intensely than that in Fig.7a.It is analyzed that the sample's surface is oxidized because the contact surface is heated by the accumulation of friction heat,which makes Sn atoms in tin-based babbit react with O atoms in air.Moreover,according to EDS analysis(Table 5),the oxide is SnO2.As lubricated film,these oxides play the role in reducing friction coefficient,but the friction coefficient would increase when the oxides were peeled off under the action of friction
Fig.7 Friction behavior of tin-based babbit layer at different conditions:a 0.5 N,300 r·min-1;b 2.0 N,300 r·min
In addition,the friction coefficient is closely related to the micro structural characteristics of tin-based babbit.The soft Sn-based solid solution would become softer,even plastical deformation takes place,due to the friction heat accumulated on the sample.The friction operation is supported by the harder SbSn and Cu6Sn5 intermetallic compound particles,which decreases the contact area and increases the toughness of contact surface
Table 5 EDS analysis of characteristic points in Fig.10 (at%)
Fig.8 Wear rate of tin-based babbit layer
The wear morphology was investigated by SEM LSCM to provide a quantitative measurement for the friction and wear of tin-based babbit.It can be directly seen from Fig.8that the wear rate decreases obviously with the welding current increasing from 50 to 90 A.As shown in Fig.9a-c,wear width,wear cross-sectional area and wear volume decrease and the wear surface becomes rougher and rougher with the welding current increasing.It is analyzed that SbSn is refined and Cu6Sn5 compounds uniformly distribute in Sn-based solution,so that the hard particles would be broken more seriously.Therefore,the wear behavior is attributed to the microstructural characteristics of the tin-based babbit and the microstructure of the tin-based babbit,which can be controlled by optimizing welding parameters.
SEM and EDS analyses were carried out to further explore the wear mechanism of the tin-based babbit.Figure 10a,b shows wear morphology at load of 2 N and speed of 300 r·min-1,and the results of characteristic points are listed in Table 5.Not only the oxide would affect the friction coefficient,but also the abrasive wear would change it.The soft Sn-based solid solution is melted because of the large amount of friction heat,and the furrow would be formed under the action of abrasive wear
3.3 Shear strength of TIG arc brazing tin-based babbit
Shear strength tests were carried out to measure the interfacial bonding property,and the results are shown in Fig.11.It can be seen that the interfacial shear strength obviously increases from 73 to 155 MPa as the welding current increases from 50 to 90 A.The interfacial bonding property is apparently strengthened with the current increasing.
Fig.9 A SEM images and inset LSCM mappings of wear morphologies of tin-based babbit at different welding currents:a 50 A,b 70 A and
Fig.10 a SEM images of wear morphology at friction and wear parameters of 2.0 N and 300 r·min-1 and b enlarged image on the hole under
Fig.11 Shear strength of TIG arc brazing tin-based babbit
4 Conclusion
In this study,TIG arc brazing was used to fabricate the tinbased babbit anti-friction layers under different welding currents.Experimental results show that the higher welding current makes it possible to form isomer structure of the SbSn and Cu6Sn5,and the higher hardness and better tribological property are due to these hard intermetallics.Oxidative wear and abrasive wear are found when applied load is 2 N.EDS analysis results show that the oxidative production is SnO2.Furrow forms on the contact surface at the softer Sn-based solid solution under abrasive wear,while harder SbSn and Cu6Sn5 will be shattered and a hole under friction is left.
参考文献
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