Talivaldis Spalvins

Frictional and morphological properties of AuMoS2 films sputtered from a compact target

Abstract AuMoS 2 films 0.02–1.2 μm thick were sputtered from a target compacted from 5 wt.% Au plus 95 wt.% MoS 2 to investigate the frictional and morphological film growth characteristics. The gold dispersion effects in MoS 2 films are of interest to increase the densification and strengthening of the film structure. Three microstructural growth stages were identified on the nano-micro-macrostructural level. During sliding both sputtered AuMoS 2 and sputtered MoS 2 films have a tendency to break within the columnar region. The remaining or effective film, about 0.2 μm thick, performs the lubrication. The AuMoS 2 films displayed a lower friction coefficient with a high degree of frictional stability and less wear debris generation compared with pure MoS 2 films. The more favorable frictional characteristics of the AuMoS 2 films are attributed to the effective film thickness and the high density packed columnar zone which has a reduced effect on the fragmentation of the tapered crystallites during fracture.

Morphological and frictional behavior of sputtered MoS2 films

Abstract From the texture and growth patterns of sputtered MoS 2 films deposited onto substrates, three regions can be distinguised: (1) a ridge formation region, (2) an equiaxed transition zone and (3) a columnar-fiber-like structure. The lubricating properties of sputtered MoS 2 films can be visually identified with respect to optical changes before and after rubbing. The orientation of the surface microcrystallites is identified, and the change in optical properties is explained. In sliding contact the sputtered film tends to break up at the base of the columnar region. Effective lubrication occurs with the film remaining on the substrate. This film is 0.18–0.22 microm thick.

Coatings for wear and lubrication

Abstract In this paper we review the recent advances in the tribological uses of r.f.-sputtered and ion-plated films of solid film lubricants (laminar solids, soft metals, organic polymers) and wear-resistant refractory compounds (carbides, nitrides, silicides). The sputtering and ion-plating potentials and the corresponding coatings formed are evaluated relative to the friction coefficient, wear endurance life and mechanical properties. The tribological and mechanical properties of each kind of film are discussed in terms of film adherence, coherence, density, grain si morphology, internal stresses and thickness and substrate conditions such as temperature, topography, chemistry and d.c. biasing. The ion-plated metallic films in addition to improved tribological properties also have better mechanical properties such as tensile strength and fatigue life.

Tribological properties of sputtered MoS2 films in relation to film morphology

Thin sputter-deposited MoS2 films in the thickness range 2000–6000 A have shown excellent lubricating properties when sputtering parameters and substrate conditions are properly selected and precisely controlled. The lubricating properties of sputtered MoS2 films are strongly influenced by their crystalline-amorphous structure, morphology and composition. The coefficient of friction can range from 0.04 which is effective lubrication to 0.4 which reflects an absence of lubricating properties. Visual screening and slight wiping of the as-sputtered MoS2 film can determine the integrity of the film. An acceptable film displays a black sooty surface appearance whereas an unacceptable film has a highly reflective gray surface and the film is hard and brittle.

Frictional and morphological characteristics of ion plated soft, metallic films

Abstract Ion-plated metallic films in contrast with films applied by other deposition techniques offer lower friction coefficients and longer endurance lives and exhibit a gradual increase in the friction coefficient after the film has been worn off. The friction coefficients of metallic films are affected by the degree of adherence, the thickness and the nucleation and growth characteristics. The effective film thickness for the minimum friction coefficient was established for gold and lead films. The nucleation and growth characteristics during ion plating lead to a fine continuous crystalline structure, which contributes to a lower friction coefficient.

Characterization of defect growth structrures in ion-plated films by scanning electron microscopy

Abstract Copper and gold films (0.2–2 μm thick) were ion plated onto polished 304 stainless steel surfaces. These coatings were examined for coating growth defects using scanning electron microscopy. Three types of defects were distinguished: nodular growth, abnormal or runaway growth and spits. The cause and origin of each type of defect was traced. Nodular growth is primarily due to inherent substrate microdefects, abnormal or runaway growth is due to external surface inclusions and spits are due to non-uniform evaporation. All these defects have adverse effects on the coatings. They induced stresses and produce porosity in the coatings and thus weaken their mechanical properties. Friction and wear characteristics are affected by coating defects, since the large nodules are pulled out and additional wear debris is generated.

Frictional and structural characterization of ion‐nitrided low and high chromium steels

Low Cr steels AISI 4140, AISI 4340, and high Cr austenitic stainless steels AISI 304. AISI 316 were ion nitrided in a dc glow discharge plasma consisting of a 75% H2–25% N2 mixture. Surface compound layer phases were identified, and compound layer microhardness and diffusion zone microhardness profiles were established. Distinct differences in surface compound layer hardness and diffusion zone profiles were determined between the low and high Cr alloy steels. The high Cr stainless steels after ion nitriding displayed a hard compound layer and an abrupt diffusion zone. The compound layers of the high Cr stainless steels had a columnar structure which accounts for brittleness when layers are exposed to contact stresses. The ion nitrided surfaces of high and low Cr steels displayed a low coefficient of friction with respect to the untreated surfaces when examined in a pin and disk tribotester.

A Vacuum (10−9 Torr) Friction Apparatus for Determining Friction and Endurance Life of MoSx Films

The first part of this paper describes an ultrahigh vacuum friction apparatus (tribometer). The tribometer can be used in a ball-on-disk configuration and is specifically designed to measure the friction and endurance life of solid lubricating films such as MoSx in vacuum at a pressure of 10−7 Pa, 10−9 torr. The sliding mode is typically unidirectional at a constant rotating speed. The second part of this paper presents some representative friction and endurance life data for magnetron sputtered MoSx films, 110 nm thick, deposited on sputter-cleaned 440C stainless-steel disk substrates, which were slid against a 6-mm-diameter 440C stainless-steel bearing ball. All experiments were conducted with loads of 0.49 to 3.6 N, average Hertzian contact pressure, 0.33 to 0.69 GPa, at a constant rotating speed of 120 rpm, sliding velocity ranging from 31 to 107 mm/s due to the range of wear track radii involved in the experiments, in a vacuum of 7×10−7 Pa, 5× 10−9 torr, and at room temperature. The results indicate ...

Tribological properties of boron nitride synthesized by ion beam deposition

The adhesion and friction behavior of boron nitride films on 440 C bearing stainless steel substrates was examined. The thin films containing the boron nitride were synthesized using an ion beam extracted from a borazine plasma. Sliding friction experiments were conducted with BN in sliding contact with itself and various transition metals. It is indicated that the surfaces of atomically cleaned BN coating film contain a small amount of oxides and carbides, in addition to boron nitride. The coefficients of friction for the BN in contact with metals are related to the relative chemical activity of the metals. The more active the metal, the higher is the coefficient of friction. The adsorption of oxygen on clean metal and BN increases the shear strength of the metal - BN contact and increases the friction. The friction for BN-BN contact is a function of the shear strength of the elastic contacts. Clean BN surfaces exhibit relatively strong interfacial adhesion and high friction. The presence of adsorbates such as adventitious carbon contaminants on the BN surfaces reduces the shear strength of the contact area. In contrast, chemically adsorbed oxygen enhances the shear strength of the BN-BN contact and increases the friction.

Tribological characteristics of gold films deposited on metals by ion plating and vapor deposition

Abstract Recent work on the graded interface between an ion-plated film and a substrate is discussed as well as the friction and wear properties of ionplated gold. X-ray photoelectron spectroscopy, depth profiling and microhardness measurements were used to investigate the interface. The friction and wear properties of ion-plated and vapor-deposited gold films were studied both in an ultrahigh vacuum system to maximize adhesion and in oil to minimize adhesion. The results of the investigation indicate that the solubility of gold in the substrate material controls the depth of the graded interface. Thermal and chemical diffusion mechanisms are thought to be involved in the formation of the Au-Ni interface. In the Fe-Au graded inter- face, gold was slightly dispersed in the iron and formed only a physically bonded interface. The hardness of the gold film was influenced by the thickness and was also related to the composition gradient between the gold and the substrate. A graded Ni-Au interface exhibited the highest hardness because of an alloy hardening effect. The effects of film thickness on adhesion and friction were established. A minimum coefficient of friction was found in the thin film region. No graded interfaces were detected in this investigation between vapor-deposited gold films and substrates.