Tribological Performance of Graphite Nanoplatelets Reinforced Al and Al/Al2O3 Self-Lubricating Composites.

Emad Omrani,Pradeep L Menezes,Ashish K Kasar,Afsaneh Dorri Moghadam,Pradeep Rohatgi

doi:10.3390/ma14051183

Emad Omrani, Pradeep L Menezes + Show 3 more

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https://doi.org/10.3390/ma14051183

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Abstract

In the present work, the effect of graphite nanoplatelets (GNPs) on tribological properties of the aluminum (Al), and Al/alumina (Al2O3) composite are studied. GNPs are multilayer graphene sheets which were used as a solid lubricant material. Two sets of composites, Al/GNPs and Al/GNPs/Al2O3 with varying amounts of reinforcements, were synthesized by powder metallurgy that involves cold compaction followed by hot compaction. The hardness of the composites increased with the addition of GNPs and Al2O3. The Al/GNPs composite with 1 wt.% of GNPs (Al/1GNPs) showed a 20% increase in hardness whereas Al/GNPs/ Al2O3 composite with 1 wt.% GNPs and 2 wt.% Al2O3 (Al/1GNPs/2Al2O3) showed 27% increases in hardness compared to the pure Al. The coefficient of friction measured at 20 N was observed to be 22% and 53% lesser for Al/1GNPs and Al/1GNPs/2Al2O3, respectively, compared to corresponding alloys without graphene Al. The X-ray diffraction and scanning electron microscopy analysis revealed the presence of GNPs at the worn surface after the tribology tests. The wear rate was also reduced significantly. In comparison with pure Al, the Al/1GNPs and Al/1GNPs/2Al2O3 composites resulted in 5- and 20-times lesser wear rate, respectively. The addition of Al2O3 caused reduction in wear rate due to higher hardness and load carrying ability, whereas composites with more than 1 wt.% GNPs showed higher wear rate due to lower hardness and higher porosity. The Al/1GNPs/2Al2O3 composite exhibited the least coefficient of friction (0.2–0.25) and wear rate (1 × 10−6–4 × 10−6 mm3/N.m) compared to other GNPs and Al2O3 reinforced Al composites. The worn surfaces were further analyzed to understand the wear mechanism by Raman spectroscopy, transmission electron microscopy, and x-ray diffraction to detect the Al4C3 phase formation, chemical bonding, and defect formation in graphene.

Highlights

The current demand to fulfil the requirement of high-performance materials is challenging with existing metals and alloys as they have limited properties
When metals are reinforced with suitable reinforcements, the manufactured metal matrix composites (MMCs) contain improved properties that can be optimized to have a wide range of properties such as being lightweight, high specific strength, high hardness, and superior tribological properties
In our previous study on pure Al-graphite nanoplatelets (GNPs) composite, we found a lower coefficient of friction (COF) with 1 wt.% GNPs in the Al matrix compared to unreinforced Al [18]

Summary

Introduction

The current demand to fulfil the requirement of high-performance materials is challenging with existing metals and alloys as they have limited properties. When metals are reinforced with suitable reinforcements, the manufactured metal matrix composites (MMCs) contain improved properties that can be optimized to have a wide range of properties such as being lightweight, high specific strength, high hardness, and superior tribological properties. It has been observed that MMC’s properties improve with a decrease in the size of the reinforcement [1,2]. The current technologies allow production of particles below 100 nm that can be used as a reinforcement to improve desired properties. A metal matrix composites reinforced with nanosized particles are termed as a metal matrix nanocomposite (MMNCs).

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