The feasibility of growing stoichiometric thin films of BN by pulsed laser evaporation has been investigated. Films grown under high vacuum conditions were N-deficient. This result is consistent with thermodynamic calculations, which indicate that B metal formation, with concomitant N2 desorption, is energetically favored over BN formation. Stoichiometric films were grown in NH3 with substrate temperatures of 400, 500, and 1000ºC. Analysis of films grown under these conditions by grazing incidence x-ray diffraction indicates the films to be highly oriented, hexagonal BN.

One of the advantages of the ion beam assisted deposition process is its controllability of the processing parameters such as: ion-to-atom arrival ratio and the ion energy. In this study, the effects of the nitrogen ion energy (from 1 KV to 30KV) on the TiN film morphology and microstructures were systematically investigated as a function of ion-to-atom arrival ratios, using TEM, XTEM, SEM, ESCA and other analytical techniques.

The alloy preferred for medical protheses, Ti6Al4V, was ion implanted with oxygen and nitrogen alone and in combination at varying energies, 25 to 120 keV, and varying dose levels, 1017 to 1018 ions/cm2. Measurements were made of microhardness, corrosion resistance, chemical bonding of implanted species, and (with UHMpWol yethylene) pin-on-disk wear and friction. The addition of oxygen to nitrogen implants now used in production was found to have little effect on wear or any other parameter.

Advances in solid lubricating films for vacuum and high temperature applications are reviewed. Traditional lubricants (e.g. graphite and dichalcogenides) are being improved and new lubricating materials (e.g. amorphous carbons) are being discovered with the aid of recent developments in deposition processes and surface analytical methods. Ion bombardmenttreatments have increased film adhesion, lowered friction coefficients and enhanced the wearlife of MoS2 films, as well as created new forms of lubricating carbons (amorphous, polymeric and diamond-like). Composite films and multilayer coating treatments are providing extra protection for surface and films against environmental degradation. Ultralow friction coefficients (<0.01) have been achieved with MoS 2 as well as diamond-like carbon films. Material selection, in some cases (e.g. thin metal films), can nowbe made basedon scientific principles, although many tribomaterials are still being developed by trialand error methods.

The relationship between the morphologies and crystal structures of sputter-deposited MoS2 films and their lubricating capabilities is discussed. In particular, aspects of plastic deformation processes are presented. Scanning elecron microscopy (top surface and cross sectional), transmission electron microscopy (lattice imaging and dark field), and x-ray diffraction techniques were used to characterize film structure. The asdeposited morphology, which can be described in terms of zone models, was found to influence the initial nature of the wear debris and the loadbearing capabilities of the films. In many cases a highly deformed region confined to the surface of the films was found. Applied stress was found to reorient crystallites and to induce crystallization, with the degree of both processes being related to the initial structure of the film. Criteria are presented for selecting the film type and preparation conditions to fit various applications.

X-ray Photoelectron.pectroscopy (XPS) and Conversion Electron M6ssbauer bpectroscopy (CEMS) were used to examine iron that was deposited on the basal plane of MoS2 single crystals and subjected to vacuum annealing, oxidizing, and reducing environments. Iron either intercalated into the MoS2 structure or formed oriented iron sulfides depending on the level of excess sulfur in the MoS2 structure. CEMS data demonstrated that iron sulfide crystal structures preferentially aligned with respect to theMoS2 basal plane and that alignment, and potentially adhesion, could be variedby appropriate high temperature annealing procedures.

Wear tests were performed under ultra high vacuum conditions in a ball-onflat configuration on magnetron sputtered and triode sputtered MoS2 films on 440C steel substrates. The issue of material loss versus deformation of the film was investigated using energy dispersive x-ray microanalyses for mass loss determinations and Michelson interferometry to measure the deformation of the tracks. Significant deformation without material loss was found in the first 10 passes. Surface composition of the tracks and the transfer film on the ball was determined by Auger electron spectroscopy. The S/Mo ratio wasfound to increase and the O/Mo ratio was found to decrease with increased sliding distance.

Studies of the tribological properties of molybdenum disulphide deposited at the high rates afforded by magnetron sputtering have shown such films to exhibit low friction and high endurance under vacuum. However such studies have mostly been confined to bearing steels. This paper reports on the extension of such studies by presenting measurements of friction coefficient and endurance obtained for thin films of “high-rate” molybdenum disulphide applied to substrates of 440C steel, 52100 steel, titanium alloy 318 andsilicon nitride. The results are interpreted in terms of substrate-related parameters such as film adhesion and elastic modulus of substrate materials. Preliminary evidence relating the degree of film adhesion to the existence of interfacial chemical compounds, identified using surface analytical techniques (XPS, SIMS), is presented.

The present paper reports on the structural and tribological studies of MoSx films in the thickness range of 3-4000 Å bombarded with inert-gas ions in the hundred-keV energy range. It has been shown that it is possible to amorphize MoS1.8 crystalline films with 400-keV Ar ions at a dose of lxl016 ions/cm2 Contrary to previous studies, there is evidence for both a lowfriction coefficient and an increased sliding life of sputtered MoSx films when amorphized by the ion-bombardment technique. The paper will discuss the influence of ion dose and tribological differences between bombarded and nonbombarded MoSx films. With the availability ofhigh-intensity ion beams in the mA range, the possibility of a direct ion synthesis of a molybdenum surface with high-intensity sulphur-ion beams will be discussed, and friction measurements of these systems will be presented.

Exposures of MoS2 to 1.5 eV atomic oxygen in an anhydrous environment reveal that the degree of oxidation is essentially independent of crystallite orientation and thesurface adsorbed reaction products are MoO3 and MoO2. A mixture ofoxides and sulfide exist over a depth of about 90 Å and this layer has a low diffusion rate for oxygen. It is concluded that a protective oxide layer will form on MoS2 upon exposure to the atomic-oxygen-rich environment of low earth orbit.

The growth and characterization of MoS thin films grown by pulsed laser evaporation is investigated. TOF anafysis of the ions evaporated from an MoS2 target indicates that PLE results primarily in the evaporation of atomic Mo and S species; MoxSy clusters were also detected, but were present at a significantly Iower intensity. TOF velocity analysis indicates an effective plasma temperature of 1500K. Stoichiometric MoS2 films were grown at substrate temperatures between room temperature and 500ºC under the above laser conditions. XPS data is used to develop a Wagner chemical state plot. Analysis of the films by Raman spectroscopy and glancing angle x-ray diffraction indicates the films to be crystalline, hexagonal MoS2, with a tendency for basal plane orientation parallel to the substrate.

Advanced structural ceramics offer unique capabilities as tribomaterials. They are being used today in diverse applications such as tips for ball-point pens, precision instrumentbearings, and cutting tool inserts. Tribological applications of ceramics can be divided into several categories based on the properties of the ceramics. These include: resistance to abrasion and erosion; resistance to corrosive wear; wear resistance at elevated temperatures; low density; and electrical, thermal and magnetic properties. Examples of present utilization of ceramics in each category are described and a few examples of potentialfuture applications are given. Many scientific and technical barriers must be overcome before the full potential of ceramics in tribological applications is realized. These barriers are discussed in terms of the limited knowledge regarding tribological performance, problems with reliability, and lack of design knowledge and experience. It is clear that the wide-spread use of advanced ceramics requires further research and development. However, it must be realized that the solutions to the scientific and technical problems will be slow.

The surface regions of α-alumina and hot pressed silicon nitride were modified by suitable alloying in order to improve their wear resistance. The surface modification in polycrystalline α-alumina was done by diffusing chromia into the surface region which resulted in the formation of a thin layer of A12O3 - Cr9O3 solid solution which has a lower thermal expansion coefficient than pure α-alumina. Also Cr2O3 has a larger lattice parameter than α-alumina thus during cooling the surface was put into compression. The surface region of hot pressed silicon nitride was modified by diffusing α-alumina into the surface which resulted in the formation of a thin sialon layer. A surface compressive stress was again introduced due to the lower thermal expansion coefficient and larger latticeparameter of sialon compared to silicon nitride.

Wear tests were conducted against 52100 steel under both lubricated and unlubricated sliding contact using a block on ring apparatus. The wear resistance of chromia surface alloyed α-alumina was improved considerably over unalloyed α-alumina under both lubricated and unlubricated conditions. The wear resistance of alumina surface alloyed silicon nitride was also improved over unalloyed silicon nitride under both lubricated and unlubricated conditions.

Different wear modes were identified by examining the worn surfaces under the scanning electron microscope.

This is Part II of a tribological study of metal/ceramic pair in a sliding contact. The tribological behavior of molybdenum against a single crystal A12O3 was investigated at bulk temperatures of 23ºC and 400ºC using a sliding speed of 4 m/s and loads from nine to twenty five Newtons. The role of oxidational wear was confirmed at both temperatures. The linear dependency of wear rate on load was identified at 23ºC tests. At 400ºC, there was a rapid increase of wear rate at a load of about 25 N possibly due to the volatilization of MoO3, which is the limitation of molybdenum oxide as a solid lubricant. However, this study showed that the out-of-contact oxide formation may have prevented the catastrophic oxidation during contact at the real area of contact. It also showed that in-situ formed molybdenum oxide has good lubricating properties (≃ 0.3) and a low wear rate (≃ 10-14 m3/m). Therefore, this molybdenum can be used for a large range of sliding speeds and loads.

The effect of surface finish on the unlubricated sliding wear behavior of a 94% A12O3 ceramic material has been investigated using a reciprocatingright cylinder-on-flat tribometer. The surface finishes evaluated were produced using a combinationof SiC and diamond abrasive particles.

Profilometry was employed to characterize surface topography and x-ray diffraction was used to determine the residual stress associated with each finishing process.

The coefficients of friction and controlling wear mechanisms varied dramatically as the maximum asperity height was altered by different finishing techniques. Below a peak profile of 0.25 μm, the coefficient of friction varied between 0.60 and 0.75 due to preferential shearing of the siliceous binder phase which segregated at surfacial pores and grain boundaries. Binder adhesion in the sliding contact produced stick-slip frictional behavior. Surfaces with asperity heights in excess of 10 μin exhibited intergranularfracture or grain “pluck-out”. These surfaces contained minimal real areas of contact and yielded friction coefficients of 0.30 - 0.35. Removed alumina grains actedas hard abrasives in the contact zone and enhanced transgranular fracture by a lateral cracking mechanism. Evidence of crack propagation as a result of Mode II and Mode III shearloading was discovered at subsurface pore sites. The influences of microindentation hardness and fracture toughness are discussed in terms of their relative importances on the observed wear behavior.

This paper describes the use of electrical resistivity to quantify the damage produced asa result of the scratching of single crystal silicon.

The change in resistivity was measured as a function of time as a scratching diamond passed between four electrical contacts of a specially designed printed circuit and while thesilicon was heated to temperatures up to 300ºC. The data shows that the resistivity increases during scratching and reaches a steady state value if the silicon temperatureis below 200ºC. The conductivity recovers when the silicon temperature is 200ºC.

An assessment of the literature indicates that in high temperature air not only titanium,but also titanium carbide (TiC) and titanium nitride (TiN) react to form rutile, the mostthermodynamically stable polymorph of titanium dioxide. It has been recently hypothesizedthat slightly oxygen-deficient rutile (TiO2-x) behaves as a low shear strength, lubricious oxide.

Although the oxidation kinetics-driven reaction of the less stable TiC results in thickeroxide layers than on TiN, the most prevalent film morphology and oxide structure on both TiC and TiN are the same as those generated on the much softer Ti and its alloys. In mostcases of static oxidation and tribooxidation at high temperatures, the oxide layers grow in extremely thin (1 to 5 μm) sheets, which periodically delaminate from the substrate. The kinetics of delamination are highly dependent on substrate properties. These sheets form an array of loosely cohering (under static conditions) or tightly cohering (under triboconditions) scales, similar to the morphology of multilayered pastry dough. The most thermodynamically stable [(110)] cleavage planes of rutile tend to align preferentially in the plane of the peeling flakes, but without any azimuthal order. It is suggested that rutile can be rendered lubricious (a) by this unique structure, (b) by keeping its shear strength minimal by intrinsic (i.e., environment-independent) control of the number of oxygen vacancies within the oxide layers, and (c) by tailoring the load-carrying substrate used to form the rutile films in-situ. Accordingly, the removal rate ofrutile and the friction coefficient provided by the oxide/substrate tribosystem may be further controlled by taking advantage of (a) the high, but still significantly different hardnesses and ideal habit plane orientation of the TiC and TiN mother matrix underlays, and (b) the differences in the reaction kinetics of layered oxide growth on these highly oriented, hard metal coating matrices at elevated temperatures, in air.

The concept of lubrication by a tribochemically generated oxide layer on the surface of silicon nitride is further investigated. Previous work has shown that low friction coefficients (μ≈0.1) are obtained in a range of sliding velocities and loads when otherwise unlubricated silicon nitride slides in humid air at temperatures between 150 and 650ºC. In order to verify the hypothesis that this behavior results from a competition between the growth of an oxide layer (with growth kinetics accelerated by friction) and its removal by wear, we have performed model experiments at room temperature, wherethe oxide layer is grown statically (i.e. without friction) and the friction coefficient and its evolution in time are subsequently measured. In order to avoid high friction by plowing, ultraflat surfaces were first prepared by sliding in water. The experiments showed that the oxide layer growing in humid air on silicon nitride produces a friction coefficient as low as μ≈0.05 that survives about 30 Newton meter of sliding, which corresponds to several hundred passes of the counterface. When sliding in water, the surface acquires a high friction coefficient (μ≈0.7) very rapidly. The difference in the lubricating properties of tribochemical surface layers on aluminum oxide and silicon nitride can be understood on the basis of the differing surface chemistries of these materials. We offer a tentative lubrication mechanism based on low adhesion between the oxide surface and the silicon nitride counterface and the structure of oxides grown inhumid ambients.

The use of ceramic materials for high temperature engine applications has prompted interest in the friction and wear characteristics of ceramicceramic pairs in mating contact. This interest has led to both surface and bulk material modifications aimed at improving the lubricity and wear resistance of these materials. This paper will discuss two basic systems developed to allow self-lubrication at high temperatures in ceramic materials through the formation of a lubricious oxide film. Both methods operate under the assumption that the oxide chemistry of the system controls the lubricity and wear properties. Relevant issues for each system will be presented and discussed.

Diamond powders, single crystal diamonds (slabs and naturally occurring stones), and CVD diamond films have been fluorinated via direct fluorination and plasma techniques at a variety of temperatures and reaction times. Infrared, ESCA, and mass spectrometric studies verify that the diamond surfaces are altered by fluorination and that fluorine is attached to the surface to some degree in most instances. Based on spectra obtained using the FT-IR techniques of DRIFTS and ATR, the fluorine appears to have an effect on the diamond surfaces at relatively low temperatures in short reaction times by the removal of surface contaminants. A relatively high temperature (600ºC) or long reaction time at slightly lower temperatures is needed to attach a significant number of fluorine atoms onto the diamond surface. Once fluorinated, the diamonds show enhanced resistance to further oxidation. The outward appearance of the diamonds remains unchanged even at fluorination temperatures nearing 800ºC.