摘要:

Friction and wear properties of silicon used in the fabrication of microelectromechanical systems (MEMS) are important for their long-term reliability. In the present study, the authors have implanted single-crystal and polycrystalline silicon wafers with boron ions to improve their mechanical and tribological properties. The authors have studied the effects of ion implantation on the crystallinity, microstructure, nanohardness, and friction and wear properties and have found that silicon remains crystalline after ion bombardment at doses up to 2 × 1017ions.cm−2but with a large amount of defects. The ion bombardment modifies elastic/plastic deformation characteristics and crack nucleation that occurs during indentation. There is a minor increase, ˜ 10-15 percent, in the nanohardness as a result of boron-ion implantation. Ion bombarded single-crystal silicon exhibits very low friction (0.05) and low wear factor (10−6mm3·N−1m−1) while slid against a 52100 steel ball. The coefficient of friction of bombarded silicon in dry air and dry nitrogen is even lower.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983335

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A model is developed to describe dynamic friction effects in lubricated surfaces. The model covers the hydrodynamic, mixed and boundary lubrication regions. The dynamic friction model can predict the friction force for time-varying velocity, and is useful in precise motion control. The model presented is for a short journal bearing, but can be extended to other geometries of sliding surfaces, such as point and line contacts or rolling element bearings. The friction is related to a time variable fluid film thickness, resulting from journal vibrations relative to the sleeve. The proposed model agrees qualitatively with experimental results for lubricated line contact. Both show similar hysteresis-type friction curves under oscillating velocity.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983336

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A numerical simulation technique for calculating the complete subsurface stress field for three-dimensionally rough bodies in sliding contact is described. The stresses are calculated using real digitized three-dimensional surface profiles. The effects of the surface roughness and the sliding friction are presented. Using an existing contact simulation code, the digitized surfaces are mathematically pressed together and the real areas of contact and the asperity pressures are calculated. The surfaces are assumed to remain elastic throughout the contact simulation process. The shear forces at the asperity contact interfaces are assumed to be proportional to their calculated normal pressures. The subsurface stresses are then determined with these known normal and tangential forces at the surface.Presented at the 48th Annual Meeting in Calgary, Alberta, Canada May 17–20, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983337

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A method for predicting scuffing failure based on the competitive kinetics of oxide formation and removal has been developed and applied to the sliding of AISI 52100 steel on steel with poly-α-olefin as the lubricant. Oxide formation rates were determined using static oxidation tests on coupons of 52100 steel covered with poly-α-olefin at temperatures of 140°C to 250°C. Oxide removal rates were determined at different combinations of initial average nominal contact pressures (950 MP a to 1578 MP a) and sliding velocities (0.4 m/s to 1.8 m/s) using a ball-on-disk vacuum tribotester. The nominal asperity flash temperatures generated during the wear tests were calculated and the temperatures corresponding to the intersection of the Arrhenius plots of oxide formation and removal rates were determined and taken as the critical failure temperatures. The pressure-velocity failure transition diagram was constructed by plotting the critical failure temperatures along isotherms of average nominal asperity flash temperatures calculated at different combinations of contact stress and sliding speed. The predicted failure transition curve agreed well with experimental scuffing data.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983338

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Mobility of molecularly thin lubricant film is an important issue in understanding boundary lubrication mechanisms and to develop reliable magnetic disk media. Intra-molecular mobility for a perfluorinated poly ether (PFPE), which is used as a disk lubricant, with two hydroxyl groups on a sol-gel SiO2surface, which is used for a protective overcoat for plated magnetic disks, was studied using nuclear magnetic resonance (NMR). Thin film viscosities for molecular segments were derived from a relaxation time. The viscosity for the hydroxyl segment is 1.8 to 11 times as much as that for a bulk lubricant at room temperature, and the viscosity rate increased with increasing temperature. For example, it increased 15 times at 100°C. The viscosities for the segments in a main chain were not different from that of bulk PFPE.

ISSN:1040-2004    

DOI:10.1080/10402009408983339

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The successful development of advanced diesel engines relies heavily on piston ring coating materials which can withstand elevated temperatures and reduce friction. Traditional hard chrome plating and flame-sprayed Mo-wire materials have reached their potential in the diesel engine environment, and alternatives are needed. Thermally-sprayed Mo-based allays and composites are being evaluated for applications as next-generation ring-face coatings. The alloy development task of producing complex Mo-based alloy powders for use as thermally-sprayed coating materials requires an understanding of their wear resistance under contact stress conditions. In this paper, the wear behavior of Mo and Mo+NiCrBSi thermally sprayed coatings is examined by pin-on-disc and single-point scratch-test methods. Microstructural analysis beneath worn regions have revealed that fracture of splats and their decohesion constitute the mode of failure. Improved wear resistance and stability of low friction coefficient was obtained by prealloying Mo with NiCrBSi prior to thermal spraying.Presented at the 46th Annual Meeting in Montreal, Quebec, Canada April 29–May 2, 1991

ISSN:1040-2004    

DOI:10.1080/10402009408983340

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A theoretical analysis has been carried out to study the capacitive effect and life estimation of hydrodynamic journal bearings on repeated starts and stops of a machine operating under the influence of shaft voltages. The analysis gives the time required for the charge accumulation and increase of charge with time on the liner surface of a journal bearing based on bearing capacitance, resistance of film thickness, and the shaft voltage. Also, it investigates the effect of gradual leakage of the accumulated charges with time as the shaft voltage falls when the power supply to the machine is switched off. This paper gives an approach to determine the ratio of the number of shaft revolutions required for charge accumulation and gradual discharge of the accumulated charges on the liner surface of a bearing depending on bearing-to-shaft voltage. Also, the number of repeated starts and stops before initiation of craters on the liner surface of a hydrodynamic journal bearing is established to restrict deterioration and damage of the liner. The diagnosis has the potential to study the transient effect of the shaft voltages on a journal bearing during the start and stop cycle of a machine.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983341

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The high-pressure rheology of a soap-thickened grease and the base oil has been characterized using a falling-body viscometer, high-pressure Couette viscometer, and a high-pressure penetrometer. At shear stress from 0.1 to 1 MPa, the response of the grease was approximately linear with rate of shear with a viscosity about twice that of the base oil. Apparent yield stress behavior is observed at lower shear stress. A new modified Bingham model is offered to describe the experimental observations. These results are relevant for simulations of elastohydrodynamic lubrication and journal bearings operating at elevated ambient pressure.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983342

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An experimental investigation was conducted to examine the dissipation of mechanical energy when machining at depths of cut less than several micrometers. Cutting and thrust forces which resulted in the orthogonal ultra-precision flycutting of Al 6061-T6 were measured over a range of depth of cut of 20 μ-m down to 0.01 μm at a cutting speed of 0.8 m-sec−1. Measurement of the tool-workpiece contact length indicated that it may become the characteristic length scale when machining al submicrometer depths of cut. Evidence suggests that the process may be viewed as transitioning from a cutting-dominant to plowing/sliding indentation-dominant process. Tool edge condition was seen to have a significant effect on the resulting forces when the depth of cut was below the tool edge radius.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24–27, 1993

ISSN:1040-2004    

DOI:10.1080/10402009408983343

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Friction and wear behavior was determined for zirconia ceramics lubricated with solid coatings (Ag, Au, and Nb) deposited by ion-beam-assisted-deposition (IBAD) techniques, and a polyol-ester-based synthetic oil. Although the use of soft Ag and Au coatings as solid lubricants in conjunction with the synthetic oil significantly reduced the fiction and wear under boundary lubrication at temperatures up to 250°C, these films had poor durability. In contrast, the Nb coating was more durable in terms of chemical reactivity and adhesion during the tribo-tests than were the Ag or Au films. However, the friction and wear behavior of the Nb-coated zirconia was poorer than that of the ceramics coated with Ag or Au.

ISSN:1040-2004    

DOI:10.1080/10402009408983344

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor