PrefaceThis report was prepared as an information resource for the development of advanced brake materials for heavy vehicles. This research is sponsored by the U.S. Department of Energy, Office of Transportation Technologies. It is part of an initiative aimed at reducing the running resistance while improving the safety of on-highway heavy trucks. Selected information on aircraft brake materials was included for comparison purposes. Data in this report have been compiled from a variety of commercial and non-commercial sources. The validity of the data in this compilation is the responsibility of the originators, and information contained herein should be used mainly as a guide and for the sake of comparison. Normally, IS0 units are used in ORNL reports, but in this case, the units have been ,reported in the measurement systems that were used in the original references. They reflect the diversity in current preferences for units of measure in the commercial brakes industry.

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Scuffing, usually considered to result from lubrication failure, severely limits the life of heavy-duty diesel fuel injectors. A new method is introduced to detect the onset of localized scuffing and monitor scuffing propagation in a fuel-lubricated ‘pin-on-twin’ reciprocating tribosystem. Tests were conducted on annealed and hardened AISI 52100 steel lubricated by on-highway #2 diesel fuel and ultra-low-sulphur Jet A aviation fuel. Unlike most current reciprocating tests that use changes in the nominal (averaged) friction to detect scuffing, this study analyses the detailed friction traces of individual strokes. The correlation between the change in the friction traces and the onset and progression of scuffing has been validated by examining the surface morphology of wear scars. This method was then applied to study the scuffing characteristics under various test conditions. Generally, scuffing initiated earlier and propagated more rapidly the higher the load, the lower the reciprocating frequency, and the poorer the lubricity of the fuel. The stroke ends, where direction reversal occurred, were especially vulnerable to scuffing due to their low sliding velocity.

This paper presents experimental evidence that thin (< approximately 200 nm) boron coatings, deposited with a (vacuum) cathodic arc technique on pre-polished Co-Cr-Mo surfaces, could potentially extend the life of metal-on-polymer orthopedic devices using cast Co-Cr-Mo alloy for the metal component. The primary tribological test used a linear, reciprocating pin-on-disc arrangement, with pins made of ultra-high molecular weight polyethylene. The disks were cast Co-Cr-Mo samples that were metallographically polished and then coated with boron at a substrate bias of 500 V and at about 100 degrees C. The wear tests were carried out in a saline solution to simulate the biological environment. The improvements were manifested by the absence of a detectable wear track scar on the coated metal component, while significant polymer transfer film was detected on the uncoated (control) samples tested under the same conditions. The polymer transfer track was characterized with both profilometry and Rutherford Backscattering Spectroscopy. Mechanical characterization of the thin films included nano-indentation, as well as additional pin-on-disk tests with a steel ball to demonstrate adhesion, using ultra-high frequency acoustic microscopy to probe for any void occurrence at the coating-substrate interface.

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