Donald H. Buckley

FRICTION AND WEAR OF CERAMICS

The adhesion, friction, wear and lubricated behaviors of both oxide and non-oxide ceramics are reviewed. 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 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.

XPS, AES and friction studies of single-crystal silicon carbide

Abstract An investigation was conducted to examine the surface chemistry and friction behavior of a single crystal silicon carbide (0001) surface in sliding contact with iron at various temperatures to 1500°C in a vacuum of 3 × 10 nPa using X-ray photoelectron and Auger electron spectroscopies. The results indicate that graphite and carbide-type carbon are seen primarily on the silicon carbide surface in addition to silicon at temperatures to 800°C by XPS and AES. The coefficents of friction for iron sliding against a silicon carbide (0001) surface were high at temperatures to 800°C. At 800°C, the silicon and carbide-type carbon are at maximum intensity in the XPS spectra. With increasing temperature above 800°C, the concentration of the graphite increases rapidly on the surface, while that of the carbide-type carbon and silicon decrease rapidly and this presence of graphite is accompanied by a marked decrease in friction. The thickness of the graphite layer is of the order of 2 nm. When the friction experiments were conducted at temperature above 800°C, the coefficients of friction were dramatically lower. The surfaces preheated to 1500°C also gave dramatically lower coefficients of friction when reheating in the sliding temperature range of from room to 1200°C. This reduction in friction is due to the graphite layer on the silicon carbide surface.

Adhesion and friction of PTFE in contact with metals as studied by Auger spectroscopy, field ion and scanning electron microscopy

Abstract The adhesion between PTFE and metals was studied by field ion microscopy, Auger emission spectroscopy and scanning electron microscopy. Strong adhesion between PTFE and all metals, both clean and oxidized, was observed with these techniques for both static and dynamic contact. The bonding is sufficiently strong so that for soft metals such as aluminum, pieces of metal can be pulled out of the bulk and embed in the PTFE subsequently causing severe scoring of the metal surfaces.

Friction and wear behavior of single-crystal silicon carbide in sliding contact with various metals

Sliding friction experiments were conducted with single-crystal silicon carbide in contact with various metals. Results indicate the coefficient of friction is related to the relative chemical activity of the metals. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to silicon carbide. The chemical activity of the metal and its shear modulus may play important roles in metal-transfer, the form of the wear debris and the surface roughness of the metal wear scar. The more active the metal, and the less resistance to shear, the greater the transfer to silicon carbide and the rougher the wear scar on the surface of the metal. Hexagon-shaped cracking and fracturing formed by cleavage of both prismatic and basal planes is observed on the silicon carbide surface. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978

Friction characteristics in vacuum of single and polycrystalline aluminum oxide in contact with themselves and with various metals.

Friction experiments were conducted in vacuum with outgassed surfaces. Experiments were made with single and polycrystalline Al2O3, sliding on themselves and in contact with metals at a sliding velocity of 0.013 cm per second, at loads to 1500 gm, temperatures to 575 C and ambient pressures to 10−10 mm Hg. These studies were made with a hemispherical or spherical rider sliding on the flat of a rotating disk. The results of the investigation indicate that (a) the friction characteristics of sapphire sliding on sapphire is highly anisotropic, (b) with metals sliding on sapphire, fracture in sapphire occurs while with polycrystalline Al2O3 shear occurs in the metal, and (c) hexagonal metals exhibited lower friction co-efficients than cubic metals in contact with polycrystalline Al2O3. Presented as an American Society of Lubrication Engineers paper at the Lubrication Conference held in Minneapolis, Minnesota, October 18–20, 1966.

Friction, Wear, and Evaporation Rates of Various Materials in Vacuum to 10(exp -7) mm Hg

The requirements for bearings and seals to operate in the environment of space dictate a new area for lubrication research. The low ambient pressures encountered in space can be expected to influence the behavior of oil, grease, and solid-film lubricants. The property of these materials most significantly affected by low ambient pressures is the evaporation rate. Various investigators have therefore measured the evaporation rates of oils and greases in vacuum as one method of establishing their relative merit for space applications (1-3). The results of this work have given some indication as to the oils and greases with the greatest stability at reduced ambient pressures. Only limited experimental work, however, has been reported in the literature for inorganic solids and soft metals which have potential use as solid lubricant films or coatings for hard alloy substrates [e.g. Reference ( 4 )]. In general, the evaporation rates of these materials would be lower than those of oils and greases. These films might therefore be very attractive as lubricants for high vacuum service.

Adhesion and friction of single-crystal diamond in contact with transition metals

Abstract An investigation was conducted to examine the adhesion and friction behavior of single-crystal diamond in contact with various transition metals and the nature of metal transfer to diamond. Sliding friction experiments were conducted with diamond in sliding contact with the metals yttrium, titanium, zirconium, vanadium, iron, cobalt, nickel, tungsten, platinum, rhenium and rhodium. All experiments were conducted with loads of 0.05 to 0.3 N, at a sliding velocity of 3 × 10 -3 m per minute, in a vacuum of 10 -8 Pa, at room temperature, and on the (111) plane of diamond with sliding in the direction. The results of the investigation indicate that the coefficient of friction for diamond in contact with various metals is related to the relative chemical activity of the metals in high vacuum. The more active the metal, the higher the coefficient of friction. All the metals examined transferred to the surface of diamond in sliding.

Friction, Deformation and Fracture of Single-Crystal Silicon Carbide

An investigation was conducted to determine the nature of the deformation and fracture of silicon carbide and its effects on friction properties. Friction experiments were conducted with hemispherical and conical diamond riders sliding on the basal plane of silicon carbide. The results indicate that, when deformation is primarily elastic, the friction does not depend on crystallographic orientation and there is no detectable fracture or crocking. When, however, plastic deformation occurs, silicon carbide exhibits anisotropic friction and deformation behavior. Surface fracture crack patterns surrounding wear tracks are observed to be or three types. The crack-geometries of two types are generally independent of orientation, the third crack, however, depends on the orientation. All surface cracks extend into subsurface. Anisotropic friction, deformation and fracture on the basal plane are primary controlled by the slip system {101¯0} ⟨112¯0⟩ and a cleavage of {101¯0}. Presented as an American Society of Lub...

Influence of Chemisorbed Films of Various Gases on Adhesion and Friction of Tungsten

An investigation was conducted to determine the effect of various absorbed gaseous species on the adhesion and friction of tungsten. Experiments were conducted in a vacuum of 10−10 Torr with a hemispherical rider specimen [(100) tungsten] contacting a flat. The atomic planes of tungsten examined on the flat included the (100), (110), and the (210). The gases absorbed to these tungsten surfaces included hydrogen, oxygen, carbon dioxide, hydrogen sulfide, and a homologous series of hydrocarbons (methane through decane), as well as ethylene and acetylene. The results of the study indicate that the presence of any gas, even hydrogen, on the tungsten surface will reduce adhesion and friction. Less than a monolayer of oxygen adsorbed on tungsten is sufficient to reduce appreciably the friction of tungsten crystals. For hydrocarbons an increase in chain length (methane through decane) resulted in a progressive decrease in friction. Furthermore, with ethane, ethylene, and acetylene, friction decreased with an inc...

Microstructure and surface chemistry of amorphous alloys important to their friction and wear behavior

Abstract An investigation was conducted to examine the microstructure and surface chemistry of amorphous alloys, and their effects on tribological behavior. The results indicate that the surface oxide layers present on amorphous alloys are effective in providing low friction and a protective film against wear in air. Clustering and crystallization in amorphous alloys can be enhanced as a result of plastic flow during the sliding process at a low sliding velocity and at room temperature. Clusters or crystallites with sizes up to 150 nm and a diffused honeycomb-shaped structure are produced on the wear surface. Temperature effects lead to drastic changes in surface chemistry and friction behavior of the alloys at temperatures up to 750°C. Contaminants can come from the bulk of the alloys to the surface on heating and impart to the surface oxides at 350°C and boron nitride above 500°C, The oxides increase friction while the boron nitride reduces friction drastically in vacuum.