Ultra-high vacuum friction experiments to simulate material transfer and wear of the platinum-rhodium proof-mass used in the GRADIO accelerometer.

Details Ultra-high vacuum friction experiments to simulate material transfer and wear of the platinum-rhodium proof-mass used in the GRADIO accelerometer. Ultra-high vacuum friction experiments to simulate material transfer and wear of the platinum-rhodium proof-mass used in the GRADIO accelerometer.

Sep 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003esasp.524..319f&link_type=abstract

In: Proceedings of the 10th European Space Mechanisms and Tribology Symposium, 24-26 September 2003, San Sebastián, Spain. Compi

Mathematics

Logic

Tribology

Scientific paper

This paper presents an original approach used to solve tribological problems encountered in the triaxial electrostatic, ultrasensitive accelerometer "GRADIO" developed by ONERA for space applications. The platinum-rhodium alloy Pt - 10% weight Rh has many significant interesting, physical and metallurgical properties (high density, low electrical resistivity, non magnetic alloy, single-phased alloy, high resistance to oxidation, relatively easy manufacturing, etc.), which make this alloy a best candidate for its use as proofmasses in ultrasensitive space accelerometers. In the GRADIO accelerometric sensor, no locking mechanism being implemented, the proof-mass is free during the launch, and despite the very reduced proofmass free motions, the induced high levels of vibrations lead the proof-mass to hit mechanical stops. The role of these stops is to avoid any contact of the proof-mass with the electrodes cage. The stops material and eventual coating shall satisfy stringent criteria related to electrical resistivity, magnetism, and so on. A preselection of acceptable materials leads to manufacture the stops in either titanium alloy Ti-6Al-4V or nickelcopper alloy ARCAP AP4 with or without coatings such as TiN, TiCN, MoS2. Vibration tests performed on development accelerometers highlighted wear debris production and material transfer between the bulk materials. These phenomena, possibly leading to perturbation of the electrostatic field and thus to reduced performances, shall be avoided. Unfortunately, such vibration tests on development accelerometers are not efficient for material and coating selection, due to cost and time consumption. For this reason, some experiments have been performed with the analytical ultra-high vacuum tribometer with linear reciprocating motion of the LTDS, reproducing as far as possible the real tribological conditions encountered between the proof-mass and the stops of the accelerometer. A good discrimination between the tested materials was achievable, highlighting the importance of deposition process for coating efficiency, especially in the case of MoS2. This easy and cheap methodology allowed us to select the better combination of materials meeting the strong operational requirements.

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