Zinc-Nickel coatings, developed in the 1980's as a replacement for zinc coatings in the automotive industry, have recently gained interest in the aerospace industry to replace cadmium coatings. Due to different material properties of Zn-Ni and Cd, there is a need to characterize Zn-Ni for tribological applications. Sliding wear tests are performed on a reciprocating pin-on-flat tribometer using a steel counterface on two Zn-Ni coatings with different microstructure and surface topography. Tests were performed under 3, 7.5 and 12 N normal loads at a relative humidity of 60 % for 2000 cycles. Increasing the normal load increased the steady state friction coefficient and wear for both coatings. The smooth and dense coating was more sensitive to the change in normal load than the rough and porous coating, as the latter experienced less wear due to the columnar structure of the coating. In contrast, the smoother and dense coating, although has less wear at low loads, has more wear at high loads due to debonding of the coating. So the coating morphology affected the extent of wear due to different wear and velocity accommodation mechanisms.

The dynamic nature of third bodies and the buried nature of a sliding contact makes it difficult to interpret and correlate changes in the coefficient of friction to instantaneous materials changes. That is, full utilization of the 'tribological circuit' as proposed by Berthier, to describe tribological flows is often limited in practice unless specialized techniques are used. In this paper, an in situ tribometer is used to understand the evolution and flow of third bodies and their effect on the coefficient of friction. The in situ tribometer consisting of a transparent sapphire countersphere coupled with optical microscope is used to study the interface during linearly reciprocating sliding with simultaneous measurement of the coefficient of friction by measuring the tangential force with a time-resolved piezo sensor at a sampling rate of 800 Hz along the track length. This provides instantaneous coefficient of friction measurements along the localized track length, allowing one to plot 'spatial friction' maps, also known as triboscopic images. These graphs are cycle number on the x-axis and track position on the y-axis with a color coding for coefficient of friction. The in situ images of third bodies are correlated with the triboscopic images to identify third body flows and how they relate to local frictional changes. A soft coating (Cd) on hard substrate (low carbon steel) is used to study these third body phenomenon.

The fabrication of carbon fiber-reinforced polymer composites generates vast amounts of waste carbon fiber. In the present work, these waste carbon fibers were added in varying contents (0.1, 0.3, and 0.5 wt%) to glass fiber/epoxy (GE) composite as short carbon fibers (SCFs) to improve its ambient and elevated temperature mechanical performance. The flexural and tensile behavior of the SCF modified GE composites were assessed at 30, 50, 70, and 110 C.The most significant improvement in mechanical performance was achieved by adding only 0.1 wt% of SCF into GE composite across most of the temperatures. At elevated temperatures, all the SCF-modified GE composites showed superior mechanical performance over the control GE composite. An important correlation between SCF content in GE composite and elevated temperature mechanical performance enhancement has been discussed. Differential scanning calorimetry was performed to understand the effect of SCF addition on GE composite's glass transition behavior. Fractography was conducted to study the various failure mechanisms at ambient and elevated temperatures.

Formation of nanocrystalline ZnO film on sliding wear tracks at high humidity levels reduces the wear.

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.