Abstract
This study examines the role of Graphene nanoplatelets (GNPs) as a solid lubricant additive to aluminum. Pure Al and Al-2 vol % GNP pellets are sintered by Spark Plasma Sintering (SPS). Their tribological properties are evaluated by a ball-on-disk tribometer at room temperature (RT) and high temperature (200 °C). Al-2 vol % GNP composite displayed poor densification (91%) and low hardness, resulting in poor wear resistance as compared to pure Al. However GNP addition resulted in a lower coefficient of friction (COF) as compared to pure aluminum at both temperatures. The results demonstrated that GNPs contribute to reducing COF by forming a protective tribolayer. GNPs also play a unique role in reducing oxygen ingress at 200 °C. It is concluded that the packing density of a starting powder blend of Al-GNP needs to be improved by using irregular shaped aluminum powder mixed with both larger and smaller GNPs. This would result in greater densification and improve wear rate while maintaining low COF.
Highlights
Overcoming friction in engine systems can significantly improve the fuel efficiency of automobiles [1,2,3]
Graphene nanoplatelets (GNPs), which consist of 20–30 graphene sheets, have revealed very low coefficients of friction, high flexibility, and wear resistance
The objective of this study is to investigate the role of GNPs as a solid lubricant additive to a pure aluminum matrix and compare its tribological behavior at room temperature and 200 ◦ C
Summary
Overcoming friction in engine systems can significantly improve the fuel efficiency of automobiles [1,2,3]. Novel aluminum alloys and composites [4,5,6], surface engineering techniques [7], and solid lubricant additives [8] have been explored to reduce friction in automotive systems. GNPs demonstrated a high ability to be dispersed into a matrix without losing 2D or mechanical properties [11]. GNP addition in an Ni3 Al matrix demonstrated 30% improvement in the coefficient of friction (COF) for temperatures between 25◦ C and 400 ◦ C [12]. Si is another matrix in which GNP improved the COF by 20% compared to that for pure Si [13]. The wear rate was 1.5 times lower for 5 vol % GNP as compared with pure Mg [14]
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