Materials and Design 24(2003) 223–226

0261-3069/03/$ - see front matter� 2003 Elsevier Science Ltd. All rights reserved.doi:10.1016/S0261-3069(03)00023-2

Technical report

Material tribo-electrification potential changing during wear

J. Tang , L. He *, Z.H. Jin , J.D. Lua a,b, a b

Department of Metallurgical Engineering, Guizhou University of Technology, Guiyang, Guizhou, P.R. Chinaa

Institute of Material Science and Engineering, Xi’an Jiaotong University, Xi’an Shaanxi, P.R. Chinab

Received 2 September 2002; accepted 23 January 2003

Abstract

During material wear test, a measurable tribo-electrification potential was found, which shows that the change of this tribo-electrification potential is closely related to the material structure, abrasive grain size and speed of friction. By this way, a newmethod for wear study has been found dynamically.� 2003 Elsevier Science Ltd. All rights reserved.

Keywords: Material; Potential; Electrification

1. Introduction

The survey method of material wear is very importantfor the study of properties of material abrasion. Usuallyabrasion resistance of a material is determined bysurveying the length change, weight change or volumechange of the sample before and after abrasion test. Allof these methods have the same characteristic, whichexpresses the material abrasion level through the changebetween initial state and final state of the test sample.These methods, however, do not produce almost anyinformation from abrasion process.

Tribo-electrification is a well-known physics phenom-enon and this effect has some thing to do with thefriction processw1–3x. The present work concentrateson the effect of electric potential varying with theabrasion condition in the test specimen. It is found thatthe test specimen can produce different electric potentialwhich vary in pattern in different wear conditions, suchas different friction speed, different abrasive size anddifferent specimen which differ in metallographic struc-ture. By this way, the information of materials abrasionwould be found dynamically.

2. Experimental procedure

The basic experimental idea is to survey the electric

*Corresponding author.

potential changing of the test specimen in the processof the abrasion. The specimen was located in an abrasivetest apparatus and isolated from the apparatus. A copperconducting wire linked the specimen with a millivolt-meter (the schematic diagram of the test apparatus isshown in Fig. 1), here the diameter of the sustain dishis 300 mm. In the experimental process, this dish wasturning in 90 cyclesymin, and the moving arm wasrunning back and forth between the center and the edgeof the dish with a speed of 300 mmymin.

In this experiment the SiC abrasive cloth was used.In order to investigate the influence of abrasive particlesize of the materials abrasion, different SiC abrasivecloths were used in which the abrasive particle sizeswere 20, 150 and 300mm, respectively. A weight of500 g was loaded onto the specimen during theexperiment.

The specimens with a diameter of 10 mm and 20 cmlong were made of medium_carbon steel and Hadfieldsteel, respectively, the condition of each specimen isshown in Table 1.

Figs. 2–5 show the triboelectric potential varying thefriction speed of all the above four specimens.

3. Discussion

The fact that triboelectric potential changed withfriction speed showed that the electric potential infor-

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Fig. 1. Schematic diagram of test apparatus:(1) Sustain dish;(2)Abrasive cloth;(3) Specimen;(4) Isolated specimen support;(5)Moving arm;(6) Millivoltmeter; (7) Weight; (8) Copper conductingwire.

Fig. 2. The triboelectric potential changes of specimen A, abrasion with different SiC abrasive cloth, the abrasive particle size are(a) 20 mm,(b) 150 mm, (c) 300 mm, respectively

Table 1Specimen condition

Specimen Materials Heat treatment state Hardness

A Medium_carbon steel 8608C quenchq550 8C temperature HRc 34B Medium_carbon steel 8608C quench HRc 60C Hadfield steel 10508C quench HB 186D Hadfield steel Cast HB 196

mation had arisen in specimens, which could be sur-veyed during the abrasion process. The level of electricpotential and its change in style are related to theabrasion condition.

When a stable friction process took place betweenthe abrasive cloth and a specimen, a triboelectric poten-tial would appear in the specimen and growth in frictionspeed increased, just as glass was rubbed with silk.During a strong abrasion process, the wear chips werebig enough, which were formed by micro cutting,grooving or brittle micro fracture, and then an oscillatorypotential curve could be obtained.

A comparison of Figs. 2–5 reveals that the abrasive

particle size had a great influence on triboelectric poten-tial. Worn with smaller abrasive particle, the processthat took place on these specimens’ surface was stablefriction or slightly plastic flow. In this case, the effectof Tribo-electrification would be obvious, so a hightriboelectric potential could be surveyed. The results ofspecimens A,B,C,D wearing with abrasive particles of20mm proved this mechanism. When the four specimenswore with abrasive particles of 150 and 300mm, theirtriboelectric potential appeared to rise and fall obviously,and the total triboelectric potential level was very low.This result may imply that the bigger wear chips haveformed as a result of micro cutting, grooving, or brittlemicro fractures.

It is shown in Figs. 2–5 that the different material ora different state of material has different triboelectricpotential in the same wear condition. Wearing withabrasive particles of 20mm, all specimens were associ-ated with a stable rising of triboelectric potential, butspecimen B had the highest triboelectric potential outof all the specimens, which may be related to the highesthardness of the specimen. The Hadfield steel specimensC and D had relatively lower triboelectric potential,which was caused by their lower hardness, which makesthe plastic flow easy.

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Fig. 3. The triboelectric potential changes of specimen B, abrasion with different SiC abrasive cloth, the abrasive particle sizes are(a) 20 mm,(b) 150 mm, (c) 300 mm, respectively

Fig. 4. The triboelectric potential changes of specimen C, abrasion with different SiC abrasive cloth, the abrasive particle sizes are(a) 20 mm,(b) 150 mm, (c) 300 mm, respectively

Worn with abrasive particles of 150mm, all thespecimens except C show a vibration triboelectric poten-tial curve. In specimen A the potential change mayindicate that the micro cutting process began in theworn surface, when micro chips(which carried someelectric charge) were cut off from the worn surface, thetriboelectric potential would drop. The triboelectricpotential of specimen B showed a rise and then fallcurve, at lower wear speed, while the potential increasedwith the rise of tribo speed. But at high wear speed the

potential obviously fell . This might be correspondingto the beginning the brittle micro fractures. Relatively,specimen C maintained a smoothly increased triboelec-tric potential in this case. This was corresponding to theoutstanding characteristics of work hardening of Had-field steel. Specimen D had cast structure, and the riseand fall curve of triboelectric potential may be relatedto the coarse grain and precipitated phase in thisstructure.

When worn with abrasive particles of 300mm, all

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Fig. 5. The triboelectric potential changes of specimen D, abrasion with different SiC abrasive cloth, the abrasive particle sizes are(a) 20 mm,(b) 150 mm and(c) 300 mm, respectively.

the specimens showed a vibration triboelectric potentialcurve, this indicates that many microchips had formedin all specimens in this wear condition.

4. Conclusions

When steel specimen is worn with SiC abrasive cloth,a tribo-electrification potential can be measured fromthe specimen. This potential varies with the wear con-dition. Be can be associated with different specimenstates, the potential varying pattern is different. Fromthis effect, the abrasion process can be surveyeddynamically.

References

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w2x Boudreaux DS, Juretschke HJ. Electronic structure of surfaces:introduction and theoretical. Honda Memorial series on mate-rials science, No.1, Structure and properties of metal surfaces.Tokyo: Maruzen company, Ltd, 1973. p. 109–116.

w3x Sasaki S. The effects of the surrounding atmosphere on thefriction and wear of alumina, zirwnia, silicon carbide andsilicon nitride. Proc Int Conf on Wear Mater, ASME1991;1:327.