Tribocontact surface exploration after friction in hexanoic acid solution

Introduction. The paper considers the evolution of friction coefficient of the pair of copper - steel alloy under friction in a hexanoic acid solution in various concentrations, and antiwear properties of the steel-steel friction pair in an oil-acidic medium. The work objective is to explore the effect of hexanoic acid additives on the tribological characteristics of friction pairs under the friction interaction in waterborne and paraffin-based formulations.

Materials and Methods. Tribological studies of a brass-steel friction pair were carried out on the AE-5 end-type friction machine. Antiwear characteristics were explored on a four-ball friction machine (FBW) in accordance with the standard GOST 9490–75. When tested at the FBW, the objective parameters of the lubricity of the oiling compositions were: welding load (Рс); wear spot diameter (Dн), critical load (Рк). Roughness parameters of the servovite film were determined through the optical profilometry; its microgeometry and structure at the nanoscale – through the atomic force microscopy. 

Research Results. Tribological properties of the brass-steel tribocoupling in aqueous media and steel-steel one in petroleum paraffin-based media are studied. The dependence of the frictional characteristics of the brass-steel friction pair on the concentration of carboxylic acid is established. Its optimum concentration is specified, which provides the effect of wearlessness. A decrease in surface roughness is revealed as a result of the frictional interaction of a brass-steel friction pair in the hexanoic acid solution compared to the initial friction surface due to the formation of a sufficiently dense layer from fine-grained copper clusters with tight particle-size dispersion. The tribological characteristics of a steel-steel friction pair were found to depend on the composition of the lubricant. It is shown that the dependence of the size of the wear scar diameter (WSD) on the acid content in the base oil is nonmonotonic in nature with a pronounced minimum at a concentration of 0.1 mass. %. The critical load (Pк) at a content of 0.05 and 0.1 mass. % increases by 32%, welding load (Pc) - by 27%.

Discussion and Conclusions. As a result of the tribological studies of a brass-steel friction pair in the hexanoic acid solution, it has been found that the optimum acid molar concentration in the lubricant composition is 0.1 mol/L. Under the frictional interaction of a brass-steel pair in the hexanoic acid solution, an antifriction copper film is formed on the friction surfaces, which contributes to a sharp decrease in the friction coefficient to 0.007 and metal wear of the friction pair to 25 times. As a result of the frictional interaction of a brasssteel friction pair in the hexanoic acid solution, a decrease in roughness is revealed compared to the initial friction surface. It is found that the frictional interaction of a brass-steel pair in the hexanoic acid solution causes a significant modification of the friction surface as a result of the deposition of finely dispersed copper clusters occurring in the lubricating medium composition and forming a servovite film. As a result of studies, it is found that the dependence of the WSD size on the acid content in the base oil is nonmonotonic in nature with a significant minimum at a concentration of 0.1 mass. %. It is shown that the addition of 0.1 mass. % of hexanoic acid into the lubricant composition exhibits the smallest wear of the steel-steel tribological pair, the WSD decreases to 0.497 mm, the critical load (Pк) and the welding load (Pc) increase by 32% and 27%, respectively.

1. Ludema, K. C. Friction, wear, lubrication: a textbook in tribology / K. C. Ludema, L. Ajayi. — CRC press. — 2018. — 82 p.

2. Hutchings, I. Tribology: friction and wear of engineering materials / I. Hutchings, P. Shipway. — Butterworth Heinemann. — 2017. — 389 p.

3. Kato, K. Wear in relation to friction–a review / K. Kato // Wear. — 2000. — Vol. 241, no. 2. — P. 151– 157. DOI : 10.1016/S0043-1648(00)00382-3

4. Liu, G. Investigation of the mending effect and mechanism of copper nano-particles on a tribologically stressed surface / G. Liu [et al.] // Tribology Letters. — 2004. — Vol. 17. — P. 961–966. DOI: 10.1007/s11249-0048109-6

5. A. Hernández Battez. CuO, ZrO2 and ZnO nanoparticles as antiwear additive in oil lubricant / A. Hernández Battez [et al.] // Wear. — 2008. — Vol. 265. — P. 422–428. DOI : 10.1016/j.wear.2007.11.013

6. Uflyand, I. E. Metal chelate monomers based on nickel (II) cinnamate and chelating N-heterocycles as precursors of nanostructured materials / I. E. Uflyand [et al.] // Journal of Coordination Chemistry. — 2019. — Vol. 72, no. 5–7. — P. 796–813. DOI : 10.1080/00958972.2019.1587414

7. Peng T. The influence of Cu/Fe ratio on the tribological behavior of brake friction materials / T. Peng [et al.] // Tribology Letters. — 2018. —Vol. 66, no. 1. — P. 18. DOI : 10.1007/s11249-017-0961-2

8. Механические свойства сервовитных пленок, формирующихся при трении в водных растворах карбоновых кислот / В. Э. Бурлакова [и др.] // Вестник Донского гос. техн. ун-та. — 2018. — Т. 18, №. 3. — С. 280–288. DOI : 10.23947/1992-5980-2018-18-3-280-288

9. Menezes, P. L. Role of surface texture, roughness, and hardness on friction during unidirectional sliding / P. L. Menezes [et al.] // Tribology letters. — 2011. — Vol. 41(1). — P. 1–15. DOI : 10.1007/s11249-010-9676-3

10. Бурлакова, В. Э. Трибологические возможности пары трения латунь-сталь в водных растворах органических кислот / В. Э. Бурлакова, Е. Г. Дроган, Д. Ю. Геращенко // Трибология-машиностроению: сб. трудов XII междунар. науч.-техн. конф. — Ижевск, 2018. — С. 92–95.

11. Бурлакова, В. Э. Влияние концентрации органической кислоты в составе смазки на трибологические характеристики пары трения / В. Э. Бурлакова, Е. Г. Дроган // Вестник Донского гос. техн. ун-та. — 2019. — Т. 19, №. 1. — С. 24–30. DOI : 10.23947/1992-5980-2019-19-1-24-30

12. Gerberich, W. W. Superhard silicon nanospheres / W. W. Gerberich [et al.] // Journal of the Mechanics and Physics of Solids. — 2003. — Vol. 51, no. 6. — P. 979-992. DOI : 10.1016/S0022-5096(03)00018-8

13. Saurín, N. Study of the effect of tribomaterials and surface finish on the lubricant performance of new halogen-free room temperature ionic liquids / N. Saurín [et al.] // Applied Surface Science. —2016. — Vol. 366. — P. 464-474. DOI : 10.1016/j.apsusc.2016.01.127

14. Jansons, E. The Impact of Ice Texture on Coefficient of Friction for Stainless Steel with Different Surface Roughness. Key Engineering Materials / E. Jansons, K. A. Gross // Trans Tech Publications. —2019. —Vol. 800. — P. 308-312 DOI : 10.4028/www.scientific.net/KEM.800.308

15. Qin, W. Effects of surface roughness on local friction and temperature distributions in a steel-on-steel fretting contact / W. Qin [et al.] // Tribology International. — 2018. — Vol. 120. — P. 350–357. DOI : 10.1016/j.triboint.2018.01.016

16. Choi, C. H. Nanoturf surfaces for reduction of liquid flow drag in microchannel / C. H. Choi, J. Kim, C.J. Kim // ASME 3rd Integrated Nanosystems Conference. American Society of Mechanical Engineers. — 2004. — P. 47– 48. DOI : 10.1115/NANO2004-46078

17. Burlakova, V. E. Nanotribology of Aqueous Solutions of Monobasic Carboxylic Acids in a Copper Alloy‒Steel Tribological Assembly / V. E. Burlakova [et al.] // Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques. — 2018. — Vol. 12, no. 6. — P. 1108–1116. DOI : 10.1134/S1027451018050427

18. Влияние состава смазочной среды на структуру поверхностных слоев формирующейся при трении сервовитной пленки / В. Э. Бурлакова [и др.] // Поверхность. Рентгеновские, синхротронные и нейтронные исследования. — 2019. — №. 4. — С. 91–99. DOI : 10.1134/S0207352819040061

19. Wolff, C. A. newly developed test method for characterization of frictional conditions in metal forming / C. Wolff, O. Pawelski, W. Rasp // Proceedings of the Eighth International Conference on Metal Forming. — Krakow. — 2000. — P. 91–97.