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At least 127 records · Page 7

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NASA NTRS1982

Tribological characteristics of a composite total-surface hip replacement

Continuous fiber, woven E glass composite femoral shells having the same elastic properties as bone were fabricated. The shells were then encrusted with filled epoxy wear resistant coatings and run dry against ultrahigh molecular weight polyethylene acetabular cups in 42,000 and 250,000 cycle wear tests on a total hip simulator. The tribological characteristics of these continuous fiber particulate composite femoral shells articulating with ultrahigh molecular weight polyethylene acetabular cups were comparable to those of a vitallium ball articulating with an ultrahigh molecular weight polyethylene acetabular cup.

Jones, W. R., Jr.↗

NASA NTRS1982

Tribological properties at 25 C of seven polyimide films bonded to 440 C high-temperature stainless steel

The tribological properties of seven polyimide films applied to 440 C high temperature stainless steel substrates were studied at 25 C with a pin-on-disk type of friction and were apparatus. The polyimides fell into two groups according to friction and wear properties. Group I polyimides had slightly lower friction but much higher wear than group II polyimides. The wear mechanism was predominately adhesion, but the wear particles were larger for group I polyimides. For most of the polyimides the transfer films consisted of clumps of compacted wear particles. One polyimide composition produced a very thin transfer film that sheared plastically in the contact area.

Fusaro, R. L.↗

NASA NTRS1982

Tribological properties of sintered polycrystalline and single crystal silicon carbide

Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

Miyoshi, K.↗

NASA NTRS1981

Anisotropic tribological properties of silicon carbide

The effects of crystallographic orientation on the tribological properties of single-crystal silicon carbide surfaces in contact with various solids are investigated for adhesive and abrasive wear processes. In the adhesive wear process, the adhesion and wear of silicon carbide is found to be markedly dependent on crystallographic orientation. The force resisting shearing fracture of the adhesive bonds at the interface is lower in preferred crystallographic direction of slip. In the abrasive wear process, the 1 0 -1 0 direction on the basal plane of silicon carbide exhibits the lowest coefficient of friction and the greatest resistance to abrasion.

Miyoshi, K.↗

NASA NTRS1982

Effect of sliding speed and contact stress on tribological properties of ultra-high-molecular-weight polyethylene

A pin on disk apparatus was used to investigate the effect of sliding speed on the friction, wear, and transfer film characteristics of hemispherically tipped AISI 440C high temperature (HT) stainless steel riders sliding against ultrahigh molecular weight polyethylene (UHMWPE) disks. The surface morphology of the wear track was studied to determine possible wear mechanisms. Geometry effects were determined by comparing the results to those of others who used different specimen configurations. The results indicate that sliding speed, sliding distance, contact stress, and specimen geometry can all markedly influence the tribological properties of UHMWPE.

Fusaro, R. L.↗

NASA NTRS1984

Tribology in the 80's. Volume 1: Sessions 1 to 4

A wide range of subjects extending from fundamental research with tribological materials and their surface effects up to the final applications in mechanical components were covered.

Source record↗

NASA NTRS1984

Status and Direction of Tribology as a Science in the 80's. Understanding and Prediction

The most challenging research problems in tribology for the next decade or beyond are classified horizontally into two categories: (1) understanding of basic mechanisms and (2) prediction of practical performance. Vertical classifications are in terms of particular themes or fields of interest. Areas where more fundamental work is required are: adhesion and friction of clean and contaminated surfaces; lubrication; new materials; surface characterization at the engineering level (topography) and at the atomic levels (various spectroscopies); and wear.

Tabor, D.↗

NASA NTRS1983

The X-ray photoelectron spectroscopy depth profiling and tribological characterization of ion-plated gold on various metals

For the case of ion-plated gold, the graded interface between gold and a nickel substrate and a nickel substrate, such tribological properties as friction and microhardness are examined by means of X-ray photoelectron spectroscopy analysis and depth profiling. Sliding was conducted against SiC pins in both the adhesive process, where friction arises from adhesion between sliding surfaces, and abrasion, in which friction is due to pin indentation and groove-plowing. Both types of friction are influenced by coating depth, but with opposite trends: the graded interface exhibited the highest adhesion, but the lowest abrasion. The coefficient of friction due to abrasion is inversely related to hardness. Graded interface microhardness values are found to be the highest, due to an alloying effect. There is almost no interface gradation between the vapor-deposited gold film and the substrate.

Miyoshi, K.↗

NASA NTRS1984

Tribology experiment in zero gravity

A tribology experiment in zero gravity was performed during the orbital flight of Spacelab 1 to study the motion of liquid lubricants over solid surfaces. The absence of a significant gravitational force facilitates studies of the motion of liquid lubricants over solid surfaces as controlled by interfacial and capillary forces. Observations were made of phenomena associated with the liquid on one solid surface and also with the liquid between a pair of closely spaced surfaces. Typical photographic records obtained on Spacelab 1 are described.

Pan, C. H. T.↗

NASA NTRS1985

Effect of counterface material type and its topography on the tribological properties of polyimide composites

Graphite fiber reinforced polyimide composite pins were slid against seven different counterfaces to determine the effect of material type on the tribological properties of polymer composites. In addition, the effect of sliding a new pin on a pre-established transfer film was investigated. The results indicated that almost a five order of magnitude difference in composite wear rate can occur just by varying the counterface material. An attempt to make all surfaces as smooth as possible was made, but due to differences in material composition this was not possible and a range of surface roughnesses were obtained. The results indicate that the smoother the surface, the lower the composite wear rate; but that small protrusions (not discernible with arithmetic surface roughness measurements) can markedly increase wear rates. A pre-established transfer film improved both run in and steady state wear rates.

Fusaro, R. L.↗

NASA NTRS1985

Tribological properties of structural ceramics

The tribological and lubricated behavior of both oxide and nonoxide ceramics are reviewed in this chapter. Ceramics are examined in contact with themselves, other harder materials and metals. Elastic, plastic and fracture behavior of ceramics in solid state contact is discussed. The contact load necessary to initiate fracture in ceramics is shown to be appreciably reduced with tangential motion. Both friction and wear of ceramics are anisotropic and relate to crystal structure as has been observed with metals. Grit size effects in two and three body abrasive wear are observed for ceramics. Both free energy of oxide formation and the d valence bond character of metals are related to the friction and wear characteristics for metals in contact with ceramics. Surface contaminants affect friction and adhesive wear. For example, carbon on silicon carbide and chlorine on aluminum oxide reduce friction while oxygen on metal surfaces in contact with ceramics increases friction. Lubrication increases the critical load necessary to initiate fracture of ceramics both in indentation and with sliding or rubbing. Ceramics compositions both as coatings and in composites are described for the high temperature lubrication of both alloys and ceramics.

Buckley, D. H.↗

NASA NTRS1986

Adequacy of surface analytical tools for studying the tribology of ceramics

Surface analytical tools are very beneficial in tribological studies of ceramics. Traditional methods of optical microscopy, XRD, XRF, and SEM should be combined with newer surface sensitive techniques especially AES and XPS. ISS and SIMS can also be useful in providing additional compositon details. Tunneling microscopy and electron energy loss spectroscopy are less known techniques that may also prove useful.

Sliney, H. E.↗

NASA NTRS1986

Characterization of the tribological coating composition 77 wt % CaF2 - 23 wt % Li F fused to IN-750 alloy

A coating composed of 77 wt % CaF2 - 23 wt % LiF fused on IN-750 nickel-based alloy was studied using SEM, XRD, EDX, and optical microscopic methods. The surfaces examined were the as-fused coating with no subsequent treatment, the coating after ultrasonic cleaning in water, and the uncoated polished and etched metal. It was found that the coating reacts during fusion with Ti and Nb rich inclusions in the alloy. Numerous small rectangular crystallites of Ca(Ti,Nb) oxide are formed beneath an overlay of fused fluoride composition. These crystallines are stubby and appear to be embedded in the metal substrate surface. It is known from previous studies that this coating-alloy system has good tribological properties in extreme conditions, such as liquid fluorine. It has been concluded from the present study that the short firmly embedded crystalline protuberances contribute to the coating adherence and thereby to enhanced coating wear life.

Deadmore, D. L.↗

NASA NTRS1987

Tribological properties of polymer films and solid bodies in a vacuum environment

The tribological properties of ten different polymer based materials were evaluated in a vacuum environment to determine their suitability for possible lubrication applications in a space environment, such as might be encountered on the proposed space station. A pin-on-disk tribometer was used and the polymer materials were evaluated either as solid body disks or as films applied to 440C HT stainless steel disks. A 440C HT stainless steel hemispherically tipped pin was slid against the polymer materials. For comparison, similar tests were conducted in a controlled air atmosphere of 50 percent relative humidity air. In most instances, the polymer materials lubricated much better under vacuum conditions than in air. Thus, several of the materials show promise as lubricants for vacuum applications. Friction coefficients of 0.05 or less and polymer material wear rates of up to 2 orders of magnitude less than in air were obtained. One material showed considerable promise as a traction drive material. Relatively high friction coefficients (0.36 to 0.52) and reasonably low wear rates were obtained in vacuum.

Fusaro, Robert L.↗

NASA NTRS1987

Mechanical strength and tribological behavior of ion-beam deposited boron nitride films on non-metallic substrates

An investigation was conducted to examine the mechanical strength and tribological properties of boron nitride (BN) films ion-beam deposited on silicon (Si), fused silica (SiO2), gallium arsenide (GaAs), and indium phosphide (InP) substrates in sliding contact with a diamond pin under a load. The results of the investigation indicate that BN films on nonmetallic substrates, like metal films on metallic substrates, deform elastically and plastically in the interfacial region when in contact with a diamond pin. However, unlike metal films and substrates, BN films on nonmetallic substrates can fracture when they are critically loaded. Not only does the yield pressure (hardness) of Si and SiO2 substrates increase by a factor of 2 in the presence of a BN film, but the critical load needed to fracture increases as well. The presence of films on the brittle substrates can arrest crack formation. The BN film reduces adhesion and friction in the sliding contact. BN adheres to Si and SiO2 and forms a good quality film, while it adheres poorly to GaAs and InP. The interfacial adhesive strengths were 1 GPa for a BN film on Si and appreciably higher than 1 GPa for a BN film on SiO2.

Miyoshi, Kazuhisa↗

NASA NTRS1986

Counterface effects on the tribological properties of polyimide composites

Fusaro, Robert L.↗

NASA NTRS1988

Tribology - A Survery Of The Science

Compendium presents six papers on tribology study of adhesion, friction, wear, and lubrication of solid materials in contact: collection of papers covering theory, practice, history, and research.

Buckley, Donald H.↗

NASA NTRS1988

Tribological Properties Of Coal Slurries

Report describes study of tribological properties of coal/methanol slurries with pin-on-disk tribometer. Coefficients of friction, rates of wear of steel pin, and morphological studies of worn surfaces conducted on pins and disks of AISI 440C HT stainless steel and M-50 tool steel, both used as bearing steels. Coal slurries considered as replacement fuels in terrestrial oil-burning facilities and possible fuels for future aircraft turbine engines. Rates of wear of metallic components through which slurries flow limit such practical applications.

Fusaro, Robert L.↗