Lubrication of Mo, W, and their Alloys with H2S gas admixtures to room temperature air
Abstract The in situ lubrication of molybdenum and tungsten using admixtures of hydrogen sulfide to room temperature and pressure air was achieved. Raman spectroscopy confirmed the presence of molybdenum disulfide and tungsten disulfide solid lubricants on elemental molybdenum and tungsten specimens, respectively. Pin-on-disk experiments were conducted with elemental molybdenum, elemental tungsten, and alloys of molybdenum and tungsten in atmospheres containing hydrogen sulfide. Friction coefficients were continuously recorded and comparisons between the sliding friction coefficient in air and in the hydrogen sulfide atmospheres were evaluated. In general, hydrogen sulfide admixtures reduced the friction coefficient for all materials containing molybdenum or tungsten. Friction coefficients for self-mated elemental molybdenum and self-mated elemental tungsten were reduced to μ =0.15 with hydrogen sulfide admixtures to air of 5% and 15%, respectively. In some cases friction coefficients as low as μ =0.08 were recorded.
Friction Behavior and Wear Analysis of SiC Sliding Against Mo in SO2, O2 and H2S at Gas Pressures Between 4 and 40 Pa
Friction tests were performed in an ultrahigh vacuum chamber with an SiC pin sliding against an Mo flat during and after exposure to gases at pressures between 4 and 40 Pa. Wear tracks, scars and debris were, analyzed ex situ with scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and transmission electron microscopy (TEM). Steady-stale friction coefficients were between 0.10 and 0.15 in SO2 and O2 gases and less than 0.01 in H2S gas; in contrast, tests performed at <10−5 Pa after H2S exposure gave friction coefficients of about 1. SEM/EDX of wear features formed in SO2 and O2 tests showed that tracks on Mo and scars on SiC were covered and surrounded by small (1–5 μm), flakelike Mo particles. In contrast, tracks formed in H2S had long stretches, of a smoothly burnished surface with very little debris. TEM of wear debris collected from both pin and flat also found only metallic Mo particles. The lubricant afforded by the gases is discussed in terms of the third-body products formed...
Tribological Properties of PM212: A High-Temperature, Self-Lubricating, Powder Metallurgy Composite
This paper describes a research program to develop and evaluate a new high temperature, self-lubricating powder metallurgy composite, PM212. PM212 has the same composition as the plasma-sprayed coating, PS212, which contains 70 wt percent metal-bonded chromium carbide, 15 wt percent silver and 15 wt percent barium fluoride/calcium fluoride eutectic. The carbide acts as a wear resistant matrix and the silver and fluorides act as low and high temperature lubricants, respectively. The material is prepared by sequential cold press, cold isostatic pressing and sintering techniques. In this study, hemispherically tipped wear pins of PM212 were prepared and slid against superalloy disks at temperatures from 25 to 850 C in air in a pin-on-disk tribometer. Friction coefficients range from 0.29 to 0.38 and the wear of both the composite pins and superalloy disks was moderate to low in the 10(exp -5) to 10(exp -6) cubic mm/N-m range. Preliminary tests indicate that the material has a compressive strength of at least 130 MPa over the entire temperature range of 25 to 900 C. This material has promise for use as seal inserts, bushings, small inside diameter parts and other applications where plasma-sprayed coatings are impractical or too costly.