Self-lubricating Al-WS2 composites for efficient and greener tribological parts

Vlad Bogdan Niste,Yanqiu Zhu,Fang Xu,Hiroyoshi Tanaka,Joichi Sugimura,Monica Ratoi

doi:10.1038/s41598-017-15297-6

Vlad Bogdan Niste, Yanqiu Zhu + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-15297-6

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Abstract

Due to their mechanical and physical properties, aluminium alloys possess wide potential in the automotive industry, particularly in hot reciprocating applications such as pistons for diesel and petrol engines. WS2 particle-reinforced composites could bring further improvements by reducing friction and wear between moving parts. Reducing friction improves efficiency by lowering energy/fuel use, ultimately leading to lower greenhouse gas emissions, while antiwear properties can prolong component life. This study compares for the first time the tribological performance of powder metallurgy-consolidated Al composites reinforced with either IF- or 2H-WS2 particles, so as to elucidate their mechanism of action in test conditions similar to those encountered in engine applications. The composites were tested in lubricated reciprocating contacts against AISI52100 steel balls and the impact of WS2 could be seen at both 25 and 100 °C. The reduced friction and wear at ambient temperature is due to the predominantly physical mechanism of action of WS2, while the best antiwear performance is measured at elevated (standard operating engine) temperatures that promote the chemical reaction of WS2 with the aluminium matrix. The investigation focused on studying the wear tracks/scars and the tribofilms generated on the composite and ball with optical profilometry, SEM, XPS and Auger spectroscopy.

Highlights

Aluminium metal matrix composites (Al MMCs) have recently gathered considerable interest in the search for light-weight materials that can offer better fuel economy, reduced vehicle emissions and increased safety
Al MMCs are composed of an Al alloy matrix and different material particle additions that modify the properties of the composite
This study has investigated the mechanism of action of Al-MMCs containing 2H-WS2 microparticles and IF-WS2 nanoparticles in lubricated contacts against a steel ball in high pressure (0.7 GPa) reciprocating contacts

Summary

Introduction

Aluminium metal matrix composites (Al MMCs) have recently gathered considerable interest in the search for light-weight materials that can offer better fuel economy, reduced vehicle emissions and increased safety. Due to the inferior tribological properties of pure aluminium, ceramic particle additions such as SiC and Al2O3 have been added to Al MMCs to increase the mechanical properties of the Al matrix[3,4,8,9,13,14] The downside of these hard additions is a high COF and their abrasiveness in the contact above a certain carried load[15]. To mitigate this aspect, particles such as graphite or tungsten and molybdenum dichalcogenides are added to reduce friction in tribological contacts due to the very low shearing forces between their weakly bonded layers of atoms. The MML has very good antiwear properties, but usually leads to a higher coefficient of friction (COF)[4,17,19,21]

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