Tribological Properties of Pyrolytic Carbon in High-Speed Tests
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Vol. 61, No. 1, May, 2020
TRIBOLOGICAL PROPERTIES OF PYROLYTIC CARBON IN HIGH-SPEED TESTS V. A. Khorev,1,2,3 V. I. Rumyantsev,1 G. A. Ponomarenko,1 A. S. Osmakov,1 and V. N. Fishchev2 Translated from Novye Ogneupory, No. 1, pp. 71 – 75, February, 2020.
Original article submitted October 4, 2019. Friction units of modern power turbines require the use of special materials with stable and low coefficients of friction under extreme conditions. Antifriction carbon-graphite materials, in particular isotropic pyrolytic carbon, are most successfully used for these purposes. Isotropic pyrolytic carbon was found to have a lower friction coefficient and wear rate than ATG-S antifriction graphite. The difference in the tribological behavior of materials was proposed to be caused by various destruction mechanisms based on an analysis of the microstructure and fractograms of wear traces. Also, isotropic pyrolytic carbon was shown to decrease the wear rate and friction coefficient with increasing density. Keywords: isotropic pyrolytic carbon (IPC), antifriction graphite, tribological tests, friction coefficient, wear rate.
perature at the contact point, system vibrations, ambient temperature fluctuations, the tested materials, etc. can considerably affect the operation of a friction unit. Therefore, model tests simulating the operating conditions must be performed for a better understanding of the processes occurring in an operating friction unit. Antifriction carbon materials (ACMs) are often used as packings to ensure the operability of friction units in dry mode. They are used because graphite cannot cause steel to seize. Also, ACMs have low elasticity moduli that prevent scoring of the surfaces of the steel opposing body [5]. Several conditions must be met for successful operation of antifriction materials at high rotation rates of the rubbing surfaces. These are the minimal sizes at various structure levels (fine-grained microstructure and minimal crystallite size), high density, high oxidation resistance, and minimal gas permeation. Friction units are fabricated from impregnated graphite parts to make them impermeable to gas. For example, ATG-S antifriction graphite is impregnated with aqueous K2O·2MnO·6P2O5 solution [2]. Isotropic pyrolytic carbon (IPC) meets the above requirements best and represents a class of turbostratic monophasic materials produced by chemical vapor deposition (CVD) via high-temperature thermal decomposition of carbon-containing gases. IPC is a high-temperature, gas impermeable, corrosion resistant construction material with strength charac-
The efficiency of friction units of power turbines is determined by their service life, economics, performance, and functional capabilities. A high linear rotation rate of the turbine rotor usually places a high load (pV-factor) on the friction units [1]. The requirements for materials operating under extreme high-speed friction modes can be identified as a low and stable coefficient of friction and high wear resistance [2]. According to GOST 27674–88, wear
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