Abstract
The fuel economy and reduction of harmful elements in lubricants are becoming important issues in the automotive industry. An approach to respond to these requirements is the potential use of low friction coatings in engine components exposed to boundary lubrication conditions. Diamond-like carbon (DLC) coatings extensively studied as ultralow friction films to protect the surfaces of ductile metals for space applications are expected to fulfil this part. The main purpose of this work is to investigate the friction and wear properties of glycerol lubricated DLC coatings under boundary lubrication conditions. The DLC material consists of tetrahedral hydrogen free amorphous diamond-like carbon (denoted as ta-C) as shown by the time of flight secondary ion mass spectroscopy (ToF-SIMS) analyses and the nanoindentation measurements. The friction coefficient below 0·.01, called superlubricity, and no measurable wear were obtained by sliding the ta-C/ta-C friction pair in the presence of pure glycerol as a lubricant at 353 K. The mechanism by which glycerol is able to reduce the friction in the millirange was revealed by ToF SIMS analyses inside and outside wear scars formed by friction experiments using deuterated glycerol and 13C glycerol.
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