Abstract
Cd coating is used in aerospace industries from last five decades due to its sacrificial protection and lubrication properties. Although Cd coating is primarily used due to its sacrificial corrosion protection when applied on steel substrate, the added benefit of modifying the tribological behavior by acting as a lubricious layer gives it a leading-edge than other coatings. Often the measurement of friction coefficient (CoF) is reported as a value generated after full sliding cycle. This measurement of average CoF generally limits the study of local variation in CoF occurring within one sliding cycle, which can be significantly different with change in spatial position due to change in third body morphology. In this study, a linearly reciprocating sliding test is used to measure the CoF at a sampling rate of 800 Hz along the track length to generate triboscopic image with steel countersphere. The instantaneous CoF obtained with triboscopy is correlated with the wear track morphology using scanning electron microscope (SEM) and optical profilometer for variation in contact conditions. Tribological test performed in dry atmosphere shows an average CoF of 0.4 till the end of the test whereas with increase in relative humidity to 60%, the average CoF changes from 0.4 to 0.8 at the end of the test due to change in contact conditions. Soft Cd coating on low carbon steel substrate is used to study these variations in third body morphology.
Highlights
Metallic coatings are commonly applied to a substrate material to prevent corrosion, either as a barrier or sacrificial layer
The major effects of changes in relative humidity were the differences in average CoF and the evolution of the average friction with time
While the regimes were observed for lower relative humidity tests, their onset was slower and were not always observed depending on test duration
Summary
Metallic coatings are commonly applied to a substrate material to prevent corrosion, either as a barrier or sacrificial layer. In terms of the tribology of Cd coatings, most researchers use standard tribology testings [3, 4], such as pin-on-disc, and report average friction versus cycle and overall wear or wear rate Testing of this sort provides an overall description of the tribological behavior but makes it difficult to examine the mechanisms behind time and spatial dependent variability of the friction or wear. Application of some soft metallic coating can act as solid lubricant [1], which lowers the CoF [3, 6, 7] These third bodies formed with metallic coatings [8,9,10,11] are dependent on the chemo-mechanical properties of the coating and the substrate. Though there have been recent work on metallic sliding [8,9,10,11, 13,14,15,16], the dynamic nature of the third bodies formed at the interface is difficult to understand and correlate with
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