Salvadore J. Calabrese

Some Parameters Affecting Tactile Friction

The friction of a sliding tactile contact was measured in an apparatus which simulated a keyboard. Results were taken for several materials. The friction coefficient was found to decrease with increasing load and with increasing speed. Experiments at varying humidity and surface roughness helped to define the friction mechanisms. It is concluded that tactile friction is predominantly adhesive, but modified by liquid bridging between the ridges of the skin and the counterface. Increased bridging due to higher humidity causes increased friction from viscous shearing effects, while increased roughness allows fewer bridges to form, decreasing the friction.

Thrust-Washer Evaluation of Self-Lubricating PS304 Composite Coatings in High Temperature Sliding Contact

PS304 self-lubricating composite coatings were successfully deposited on steel substrates at various plasma spray facilities using mixtures blended from commercially obtained constituent particles. Coatings were evaluated in thrust-washer tests against Inconel X-750 at low contact pressures to 40kPa, sliding speed of 5Amis, and either ambient temperature or 500 °C chosen to simulate conditions in airfoil bearings during startup and shutdown contact. Wear factors for all PS304 coatings tested, regardless of contact pressure and temperature, ranged from 1–3*10−4 mm3/Nm while coefficients of friction of approximately μ =0.5 were measured in all cases. While wear and friction behavior of PS304 in air foil bearings appear to have been simulated, surface roughening was observed in these thrust-washer tests which used continuous sliding contact, as opposed to the evolution of smoother surfaces observed in high-temperature foil bearings experiencing cyclic startup/shutdown. Wear-induced surface smoothening of PS304 was additionally simulated in thrust-washer tests with sliding contact instead imposed intermittently.

Dynamic Wear Tests in the SEM

Wear studies were conducted in the chamber of a scanning electron microscope (SEM) to permit direct observations of the wear processes. The sliding specimens had been metallographically polished and etched prior to test so that the effect of the alloy micro-structures could be observed. Test alloys included: low and high carbon steels, stainless steels, and bronze. As wear particles were generated, and became trapped in the interface, they produced surface damage which was in the form of material removed, or metal transfer to one of the sliding members. Video tape records were made at magnification up to 8000X and photomicrographs were taken at higher magnification to show the geometry of the wear particles. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Lubrication Conference in Washington, D.C., October 5–7, 1982

The Measurement of Surface Temperature in Dry or Lubricated Sliding

This paper describes the development and calibration of an original test apparatus to study the effect of frictional heating on lubricant effectiveness. The configuration used the Seebeck effect between a stainless steel ball and a disk of tool steel. Good agreement was found between the average temperature rise indicated by the thermoelectric voltage and Archards models. Surface temperature rises approaching 200 o C were obtained in lubricated contact and an upper bound temperature of 830 o C was found in dry contact. The likely effect of track heating was assessed by analysis and,,for this configuration, was found to be negligible

Modification of SEM for In-Situ, Liquid-Lubricated Sliding Studies

Modifications to an existing scanning electron microscope (SEM) are described which allow wear experiments to be performed inside the SEM chamber with a low vapor pressure hydrocarbon oil as the lubricant. Continuous video tape records and photomicrographs at magnifications up to 6000 × were made for several preliminary sliding experiments of steel us steel with an in-situ pin-on-cylinder test apparatus. The contact areas of steel sliding surfaces could be imaged through the lubricant film allowing observation of the deformation process as well as lubricant flow behavior. Continuous monitoring of the coefficient of friction allowed correlations to be drawn between friction data and cylinder surface topography. Comparisons in friction and wear were also made between dry and lubricated contacts. Presented as an American Society of Lubrication Engineers paper at the ASME/ASLE Tribology Conference in Pittsburgh, Pennsylvania, October 20–22, 1986

High Velocity Oxyfuel Deposition for Low Surface Roughness PS304 Self-Lubricating Composite Coatings

Efforts were made to achieve lower (R q < 0.1 μm) initial RMS roughnesses of PS304 coatings so that they may be considered for foil bearings operating under increasingly severe conditions that result in smaller air film thicknesses. Attainable roughness of conventional plasma-sprayed PS304 coatings has been typically R q > 0.25 μm, as limited by porosity in the deposited coating and surface irregularities correspondingly formed upon finishing. Initial attempts at achieving dense coatings by instead using a high-velocity oxyfuel (HVOF) flame-spraying process failed due to insufficient heating and softening of the NiCr and Cr 2 O 3 constituents of the PS304 feed powder, which rebounded from the steel target substrate and resulted in low deposition yield. Efficient HVOF deposition by a hydrogen-fueled system was achieved using NiCr and Cr 2 O 3 constituent particles of reduced size that were more effectively heated. The resultant dense coatings provided roughnesses as low as R q = 0.05 μm upon polishing. Tribological performance of these HVOF coatings was evaluated against Inconel X-750 in thrust-washer tests at a sliding speed of 5.4 m/s, with contact pressures of 20 and 40 kPa, and ambient or 500°C temperatures. The wear and friction performances in direct sliding contact, as would exist upon loss of separating air-bearing film, of the PS304 coatings produced by HVOF are found to be similar to those deposited by the plasma spray process.

Lubrication of Silicon Nitride in a Simulated Turbine Exhaust Gas Environment

Testing has been conducted on silicon nitride (Si 3 N 4 ) in simulated engine exhaust gas environments in four-ball rolling contacts and pin-on-disk sliding contacts to 590°C. Utilizing a steel race, the depth of the wear track formed at the Si 3 N 4 /Si 3 N 4 rolling contact in the presence of exhaust gas was roughly one-half that formed in the presence of N2 alone, Deposition of lubricous microcrystalline graphite carbon from CO within the exhaust was confirmed by Raman spectroscopy. Removal of H 2 O from the exhaust gas further reduced rolling wear. Exhaust gas alone provided no benefit to Si 3 N 4 /Si 3 N 4 sliding contacts, where the rate of wear greatly exceeds the rate at which lubricous carbon may deposit from the exhaust environment. As compared to that measured in the presence of N 2 alone, the directed admixture of hydrocarbon (C 2 H 2 ) to the exhaust gas enhanced the lubrication of Si 3 N 4 with reductions of up to 25 fold in rolling wear, 650-fold in steady-state sliding wear rate and 20-fold in sliding friction.

Steel Hardness Effects in Boundary Lubricated Sliding: An In-Situ SEM Study

A pin-on-cylinder test apparatus was used to perform low speed, steel-on-steel sliding experiments in-situ in a scanning electron microscope (SEM). Through modifications to the SEM, these experiments could be run with a thin film of hydrocarbon oil applied to the sliding surface. Studies have been performed using AISI 4340 steel, both annealed and through hardened, for the pin and cylinder in combinations of soft (annealed)-versus-soft, hard-versus-soft and hard-versus-hard. All three material combinations show a progressive smoothing in the wear truck as the number of sliding passes increases, plus agglomeration of wear debris interspersed with oil around the contact. Both of these effects lead to failure of the contacts due to insufficient lubrication. The combinations involving annealed steel fail catastrophically by an apparent third body abrasive mechanism while the failure of the hard versus hard combination involves intermittent plowing, resulting in more localized damage. Presented as a Society of...

A study by scanning electron microscopy of magnetic head-disk interface sliding

Abstract A test apparatus was designed and built which would allow direct observations of a sliding experiment between a magnetic tape and a ceramic head material. The tests were performed inside the chamber of a scanning electron microscope. The resulting observations and energy-dispersive analysis are discussed in this paper.

The Effect of Frictionally Generated Heat on Lubricant Transition

A study was performed to establish the transition temperature of two additives in cetane under severe conditions of pressure × velocity, which gave a surface temperature rise within the contact of up to 150°C. The interface temperature was measured using the slider as one leg of a thermocouple and the disk as the other; hence, an accurate interface temperature could be determined as the velocity and load varied. The test specimens were M50 tool steel, AISI 52100 steel and type 440C stainless steel balls against a fully hardened tool steel disc. The results complemented previous work which showed the identical trends but at slightly different absolute temperature levels.