Atmospheric plasma sprayed (APS) CuNiIn coatings have been widely used for fretting wear protection in many important areas such as aircraft engines for decades. The oxides in CuNiIn coating prepared by APS hinder splat bonding formation and thus degrade the coating fretting performance. In this study, CuNiIn powders of different boron contents were designed to realize the self-oxide-cleaning effect for in-flight molten droplets and thus deposit the dense CuNiIn coating with high fretting performance. Scanning electron microscope was used to characterize the microstructure. The oxygen content in the coating was measured by the inert gas fusion technique. Fretting test was performed for three coatings under different loadings. The results show that CuNiIn2B and CuNiIn4B coatings presented the oxide content of 0.40wt% and 0.38wt%, which are lower than 1.6wt% of the CuNiIn coating. The oxygen content in the CuNiIn4B coating decreased with the increase of spray distance while the oxygen content in CuNiIn coating increased with the increase of the spray distance. Such results clearly reveal the boron in-situ deoxidizing effect of inflight molten droplets. As a result, the dense CuNiIn2B and CuNiIn4B coatings were deposited with oxide-free molten droplets. The test results showed that the fretting wear performance of B-alloyed CuNiIn coatings were increased by a factor over three comparing with conventional CuNiIn coating.

Cu and Cu-MoS 2 coatings were fabricated by cold gas dynamic spray and the fretting wear performance of the two coatings was compared. A mixture (95 wt.% Cu + 5 wt.% MoS 2 ) was used as feedstock for the composite coating. Coatings were sprayed with identical gas flow conditions on the substrates preheated to approximately 170°C. The cross section of the coatings was analyzed by scanning electron microscope (SEM) and MoS 2 concentration was measured, as well as coating microhardness. Fretting tests were carried out under gross slip conditions in ambient environment. SEM observation on wear scars and counterspheres revealed the development of third bodies, by which the sliding was accommodated. For the Cu-MoS 2 coating, solid lubrication effects in the form of friction drops occurred in early cycles (< 5k), but eventually (> 5k) the coating's friction behavior was similar to the pure Cu coating. Third body morphology and wear of the two coatings were distinctly different, which could largely be attributed to the hardness reduction of the Cu-MoS 2 composite due to poorly bonded interfaces induced by the effect of MoS 2 during particle impact and coating formation.

In many aeronautical applications such as in the fan blade / disk dovetail notch, two parts made up of a titanium alloy are in contact and relative motion between them can occur. Titanium alloys like Ti-6Al-4V are promising candidates for tribological application because of their low weight and high specific strength. However, because of the poor tribological behavior of Ti-6Al-4V under self-mating conditions, modification of the surface has become imperative. In this work, we report on the fretting wear of plasma sprayed Cu-Ni- In along with MoS 2 solid bonded lubricant and Ti-6Al-4V. Substrate coated pins were tested against a flat plate of Ti- 6Al-4V alloy. The effect of temperature and frequency on fretting wear of Cu-Ni-In, the composite coating and Ti-6Al- 4V was investigated. Wear properties of the coatings and substrate were evaluated. The morphologies of the worn surfaces and surfaces beneath the worn surfaces were characterized with the help of an optical microscope, scanning electron microscope, electron probe micro analyzer and energy dispersive spectroscopy. Results showed that the composite coating exhibited better fretting resistance than the Cu-Ni-In plasma sprayed coating with no additive. It also exhibited lower surface roughness and a lower coefficient of friction than Cu-Ni-In or Ti-6Al-4V under the same testing condition. Therefore, the use of MoS 2 solid bonded coating scan be considered as one of the possible simple and cheap approaches for reducing fretting wear.

The sliding wear behavior of thermally sprayed aluminum oxide is fairly well studied, but little is known about its fretting behavior under cyclic tribological loads. This study investigates the fretting behavior of plasma sprayed alumina and the related influence of TiO 2 additions. Three Al 2 O 3 -TiO 2 composites are sprayed on steel substrates using commercial powders and the resulting layers are characterized based on hardness, porosity, surface morphology, phase composition, and fretting behavior. The results of the study show that TiO 2 additions reduce microhardness and increase coating toughness. The effect of TiO 2 on fretting behavior and surface wear is assessed after 10, 50, 100, 250, and 500 load cycles based on SEM imaging, friction measurements, and debris formation. Observations and test results are presented and discussed. Paper includes a German-language abstract.

Air plasma sprayed tungsten carbide-cobalt coatings are being used at Kelly Air Force Base for a fretting application for convergent seals in aircraft engines. Experimental and analytical studies were conducted to investigate the plasma spraying of two powders for this application. Statistical processing schemes were accomplished in conjunction with analytical modeling of the air plasma spray (APS) process. Classical and statistically designed experiments (SDE) chosen to be conducted were determined by analytical modeling. The coatings were characterized for composition, hardness, porosity, surface roughness, deposition efficiency, and microstructure. Attributes of the coatings are correlated with the changes in operating parameters. Wear screening of the coatings from the experiments was conducted using an abrasion tester based on ASTM Standard Test B611-85.