Solid Lubricant Material Research Articles

Propriétés tribologiques de revêtements et couches minces anti-frottement à haute température

Low friction coatings of tenth μm in thickness operating at high temperatures are composed of either metal oxides (PbO, CdO) or alkaline earth metal fluorides (CaF 2, BaF 2). These oxides and fluorides can be associated with other solid lubricant materials such as graphite or silver to extend the service temperature range from room temperature to about 800°C. Sliding contacts can also be lubricated by thin films of solid lubricant materials (silver, calcium fluoride) and Ag/CaF x ( x − 1.85) multilayer structures of 0.1 to a few μm thick produced by sputtering. The friction coefficient of these thin films was deduced from ball-on-disk tribological tests conducted at room temperature and 500°C in room air. The average friction coefficient value of silver and CaF x films in the range 0.14 to 0.42 was dependent on the film thickness and test temperature. The friction coefficient of Ag/CaF x multilayer structures was stable at about 0.35 at room temperature and 500°C. Furthermore, plan-to-plan tribological tests of thick (300 μm) plasma-sprayed coatings (PS-212 type) and CaF x thin films deposited on Cr 3C 2 underlayers were performed in room air at 500°C and 700°C. The friction properties of these thick coatings and thin films were determined and compared. The excellent performance of lubricant thin films demonstrates the interest of sputter-deposited Ag and CaF x films in lubrication of precision tolerance mechanical components operating in hostile environment.

Nanocoatings on Cutting Tools For Dry Machining

Novel material systems for coatings on cutting tools, towards accomplishing clean manufacturing, i.e. without the use of a cutting fluid, are presented. They involve use of multilayer nanocoating architectures of carbide/metal or solid lubricant/metal on cemented carbide tools by physical vapor deposition (PVD) process, namely, magnetron sputtering. By providing numerous (literally hundreds of layers) alternate nanolayers of hard and tough, hard and hard, or solid lubricating and tough materials, it is possible to take advantage of the unique properties of nanostructures, namely, higher hardness, higher strength, higher modulus, higher wear resistance, higher fracture toughness, higher chemical stability, and reduced friction than their counterparts where the coating layer thickness is in the micrometer range. Various features of these coatings are discussed from the point of view of their application in dry machining.

A Numerical Simulation of Pulsed Laser Deposition

AbstractA numerical simulation of the pulsed laser deposition process has been developed. This model is applied to pulsed laser deposition of carbon, a solid lubricant material. At laser fluences above the ablation threshold, the vapor density and temperature at the substrate are sufficiently high that a continuum flow exists. For typical pulsed laser deposition parameters, plume vapor temperatures and densities are insufficient for significant ionization. However, plume absorption does take place and is regulated by wavelength dependent absorption cross sections of the molecular species. Vapor expansion velocities depend on the absorption of laser radiation and thus the laser wavelength. A simple kinetic theory of deposition predicts the film deposition rate and film thickness profile.

TEM sample preparation of wear-tested room-temperature pulsed-laser-deposited thin films of MoS2 by ultramicrotomy

Pulsed laser deposition (PLD) is a novel technique for the deposition of tribological thin films. MoS2 is the archetypical solid lubricant material for aerospace applications. It provides a low coefficient of friction from cryogenic temperatures to about 350°C and can be used in ultra high vacuum environments. The TEM is ideally suited for studying the microstructural and tribo-chemical changes that occur during wear. The normal cross sectional TEM sample preparation method does not work well because the material’s lubricity causes the sandwich to separate. Walck et al. deposited MoS2 through a mesh mask which gave suitable results for as-deposited films, but the discontinuous nature of the film is unsuitable for wear-testing. To investigate wear-tested, room temperature (RT) PLD MoS2 films, the sample preparation technique of Heuer and Howitt was adapted.Two 300 run thick films were deposited on single crystal NaCl substrates. One was wear-tested on a ball-on-disk tribometer using a 30 gm load at 150 rpm for one minute, and subsequently coated with a heavy layer of evaporated gold.

Effect of phosphate coatings on fatigue crack initiation in quenched and tempered low-alloy steel. Technical report: Farrara, R.A. and Ritter, J.C. Materials Research Laboratories (Australia) Report No AD-A230 871/6/XAB Dec. 1990 22 pp

Due to severe operating conditions and long lifetime requirements for mechanical components, the great challenge is to develop coatings with anti-wear and high load support capability. The designs for nanocomposite protective coatings are very promising and provide an attractive alternative to take into account the multilayer architecture. In this work, a-C(Al)-based nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were constructed by Cr/CrN/CrCN multilayer. The microstructure, mechanical properties, friction and wear behaviors for these multilayer coatings were systemically investigated. Results showed that the top-layered nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were dominated by typically nanocrystallite/amorphous microstructure, and these nanocomposites constructed by multilayer approach presented superior mechanical properties which possessed relatively high hardness, low internal stress as well as high adhesion strength. Particularly, the as-fabricated nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) multilayer coatings exhibited superior anti-wear capability under relatively high applied Hertzian contact pressure compared to corresponding monolayer coatings. The improvement in friction and wear performances of as-fabricated multilayer coatings was mainly attributed to superior mechanical properties and formation of graphitized tribofilm as well as high load support capability by multilayer architecture, indicating that these coatings might be good candidates as solid lubrication materials in engineering applications.

The corrosion fatigue of the outlet pipes in the first-stage ammonium carbamate pumps: Huang, Y. Huagong Jixie (Chem. Eng. Mach.) 1991 18, (1), 53–56 ( in Chinese)

Due to severe operating conditions and long lifetime requirements for mechanical components, the great challenge is to develop coatings with anti-wear and high load support capability. The designs for nanocomposite protective coatings are very promising and provide an attractive alternative to take into account the multilayer architecture. In this work, a-C(Al)-based nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were constructed by Cr/CrN/CrCN multilayer. The microstructure, mechanical properties, friction and wear behaviors for these multilayer coatings were systemically investigated. Results showed that the top-layered nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were dominated by typically nanocrystallite/amorphous microstructure, and these nanocomposites constructed by multilayer approach presented superior mechanical properties which possessed relatively high hardness, low internal stress as well as high adhesion strength. Particularly, the as-fabricated nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) multilayer coatings exhibited superior anti-wear capability under relatively high applied Hertzian contact pressure compared to corresponding monolayer coatings. The improvement in friction and wear performances of as-fabricated multilayer coatings was mainly attributed to superior mechanical properties and formation of graphitized tribofilm as well as high load support capability by multilayer architecture, indicating that these coatings might be good candidates as solid lubrication materials in engineering applications.

Corrosion fatigue process of 12Cr stainless steel: Ebara, R., Yamada, T. and Kawano, H. ISIJ Int. July 1990 30, (7), 535–539

Due to severe operating conditions and long lifetime requirements for mechanical components, the great challenge is to develop coatings with anti-wear and high load support capability. The designs for nanocomposite protective coatings are very promising and provide an attractive alternative to take into account the multilayer architecture. In this work, a-C(Al)-based nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were constructed by Cr/CrN/CrCN multilayer. The microstructure, mechanical properties, friction and wear behaviors for these multilayer coatings were systemically investigated. Results showed that the top-layered nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) nanocomposites were dominated by typically nanocrystallite/amorphous microstructure, and these nanocomposites constructed by multilayer approach presented superior mechanical properties which possessed relatively high hardness, low internal stress as well as high adhesion strength. Particularly, the as-fabricated nc-TiC/a-C(Al), nc-CrC/a-C(Al) and nc-WC/a-C(Al) multilayer coatings exhibited superior anti-wear capability under relatively high applied Hertzian contact pressure compared to corresponding monolayer coatings. The improvement in friction and wear performances of as-fabricated multilayer coatings was mainly attributed to superior mechanical properties and formation of graphitized tribofilm as well as high load support capability by multilayer architecture, indicating that these coatings might be good candidates as solid lubrication materials in engineering applications.

Use of solid-lubricating materials to increase the life of drill bit bearing elements

Use of solid-lubricating materials to increase the life of drill bit bearing elements

Design and test of a multi-joint remote manipulator for use in high vacuum

Abstract A multi joint remote manipulator was considered for use for the inspection of in-vessel components of fusion devices. In designing the in-vacuum manipulator, the major technical issues are the selection of lubrication methods and materials for movable parts and the introduction of extrication mechanisms which work in case of accidental failures. A performance test was made on a single joint with two axes. A special hydrocarbon grease was used as the lubricant since no solid lubricant materials endure the strong forces on the gears of the joint. Wire made from shape-memory alloy was utilized for the extrication mechanism. It has been demonstrated that the manipulator works well, in vacuum, for more than 1400 h.

A New Brushless D-C Torque Motor System with Integrated Controller

A brushless d-c motor system with a unique position-sensing device has been developed. This position-sensing device works on the principle of varying magnetic reluctance and is called a reluctance switch. The reluctance switch consists of a magnetic structure excited by a high-frequency oscillator. Sensing windings on the stator sense the position of the salientpole rotor which is mechanically attached to the motor rotor. The reluctance switch, in addition to the commutation function, makes simple the incorporation of speed control by pulsewidth modulation or position control. Other unique control functions can be obtained with modifications. The developed motor is a torque motor intended for operation in space. Solid lubricant bearings and materials reflect this intended environment. The motor utilizes a permanent-magnet rotating field with a three-circuit stationary armature. The armature is driven from a three-phase transistor bridge which in turn is driven by the rectified, filtered signals from the reluctance-switch sensing windings. Reversibility and voltage speed control were requirements. This paper covers the design of the reluctance switch and the control circuits for the motor. Ripple torques and magnetic cogging torque are discussed. The unique design features of the motor are covered. The incorporation of position control, speed control, and other unique control functions are emphasized. The motor was developed at the Westinghouse Aerospace Electrical Division on Contract No. NAS5-3934 for the NASA Goddard Space Flight Center.

Fluoride Solid Lubricants for Extreme Temperatures and Corrosive Environments

Fluorides of the alkali metals and the alkaline earth metals have an interesting combination of properties that make them promising candidates as solid lubricant materials for use at high temperatures and in corrosive environments. They are chemically inert in strong oxidizing or reducing environments; they are relatively soft and nonabrasive; and some of them, such as CaF2, have planes of perfect cleavage in their crystal structure suggesting low-shear strength and good friction properties. Thin, fused fluoride coatings (0.001 inch) were applied to nickel-chromium alloys by spraying water slurries of the fluorides on the bearing surface, drying it, then firing it in a hydrogen atmosphere. Coatings of CaF2-LiF mixtures and of CaF2-BaF2 mixtures were effective as solid lubricants in hydrogen to 1500 F and in air to 1200 F. The CaF2-BaF2 coatings were effective solid lubricants in liquid sodium at 1000 F and a sliding velocity of 2000 ft/min.

Evaluation of Dry Powdered Lubricants at 1000 F in a Modified Four-ball Wear Machine

The friction and wear behavior of selected solid lubricants and wear specimens has been studied in a modified four-ball wear machine. Data were obtained at 1000 F for sliding speeds of 120 and 700 ft per min under initial Hertzian contact stresses of about 250,000 psi. Conventional solid lubricant material ssuch as lead oxide (litharge), molybdenum disulfide, and graphite were evaluated. A new dry solid lubricant, metal-free phthalocyanine, was studied and was usually found to have superior lubricating ability. Wear specimens of AISI Type M-1 tool steel and titanium carbide-nickel-molybdenum cermet showed the most promise for high-temperature sliding systems. Initial coefficients of friction less than 0.1 were obtained with combinations of these materials. Contributed by the ASLE Technical Committee on Lubrication Fundamentals and presented at the Annual Meeting of the American Society of Lubrication Engineers held in Buffalo, New York, April, 1959.