Surface effects in adhesion, friction, wear, and lubrication

643 Pages·1981·30.67 MB·English

by  Donald H. Buckley (Eds.)

SURFACE EFFECTS IN ADHESION,
FRICTION, WEAR, AND LUBRICATION
SURFACE EFFECTS IN ADHESION,
FRICTION, WEAR, AND LUBRICATION
TRI BOLOGY SE R I ES
Advisory Editor: DOUGLAS SCOTT
Editorial Board
W.J. Bartz (Germany, F.R.G.) I.V. Kragelskii (U.S.S.R.)
C.A. Brockley (Canada) K.C. Ludema (U.S.A.)
E. Capone (Italy) A.J.W. Moore (Australia)
H. Czichos (Germany, F.R.G.) G.W. Rowe (Gt. Britain)
W.A. Glaeser (U.S.A.) T. Sakurai (Japan)
M. Godet (France) J.P. Sharma (India)
H.E. Hintermann (Switzerland)
Vol. 1 Tribology - A Systems Approach to the Science and Technology of Friction,
Lubrication and Wear (Czichos)
Vol. 2 Impact Wear of Materials (Engel)
Yol. 3 Tribology of Natural and Artificial Joints (Dumbleton)
Vol. 4 Tribology of Thin Layers (Iliuc)
Vol. 5 Surface Effects in Adhesion, Friction, Wear, and Lubrication (Buckley)
TRIBOLOGY SERIES, 5
SURFACE EFFECTS
IN ADHESION,
FR IC TI0 N , WEAR,
AND LUBRICATION
DONALD H. BUCKLEY
National Aeronautics and Space Administration, Lewis Research Center, Cleveland,
Ohio USA
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
Amsterdam - Oxford - New York 1981
ELSEVIER SCIENTIFIC PUBLISHING COMPANY
1, Molenwerf, 1014 AG Amsterdam
P.O. Box 21 1,1000 A€ Amsterdam, The Netherlands
Distributors for the United States and Canada:
ELSEVIER NORTH-HOLLAND INC.
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New York, N.Y. 10017
Library of Congresa Cataloging in Publication Data
Buckley, Donald H.
Surface effects in adhesion, friction, wear,
and lubrication.
(Tribology series ; 5)
Includes bibliographies and indexes.
1. Surfaces (Technology) 2. Tribology.
3. Adhesion. I. Title. 11. Series.
T% 18.7. B76 62 1.8' 9 81-2331
ISBN 0-444-41966-7 AACRZ
ISBN: 044441966-7 (Val. 5)
ISBN: 0444416773 (Series)
0 Elsevier Scientific Publishing Company, 1981
All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or
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Printed in The Netherlands
Preface
Lubrication has emerged as a science principally since World War 11.
Prior to that, a number of fundamental contributions had been made by
DeVinci, Coulomb, Reynolds, Amontons, Hardy, Bowden, and Tabor.
From a scientific viewpoint, however, the most significant contributions, as
well as the greatest number of contributions, have been made since World
War 11.
The war effort itself was responsible for initiating a number of efforts to
try and understand the fundamental nature of surfaces and their interac-
tions in sliding, rolling, and rubbing contact. An example of this was the
development during World War I1 of adjuvants for carbon bodies to im-
prove their wear resistance in high altitude aircraft generator applications.
Basic researchers found that moisture in the carbon was critical to its
lubrication. Therefore, the presence of moisture on the surface of the car-
bon was important. With it present, the carbon lubricated very effectively
and very low wear was observed. In its absence, however, extremely high
wear occurred and what was commonly called dusting of the carbon took
place. With a fundamental study of the surface behavior of the carbon it
was discovered that something had to be substituted for the moisture that
was imparting the good lubricating characteristics to the carbon. The im-
portance of surfaces became readily apparent.
After World War 11, the need in the aircraft industry for liquid lubricants
to substitute for the conv.entionally used mineral oils dictated the studying
of synthetic materials. Again, the fundamentals and the basic structure of
organic compounds became important, and studies began on the basic
mechanism of the molecular structure in the lubrication of solid surfaces.
As a result of those studies, synthetic lubricants were developed for aircraft
applications; currently, most aircraft use synthetic lubricants for lubricating
aircraft engine components. The study of the synthetic lubricants
necessitated understanding the fundamental interactions of the synthetic
molecular structure with the solid surface so that the lubrication of solid
surfaces could be understood.
Prior to the late 1950’s it was extremely difficult to gain any fundamental
understanding of or to study solid surfaces because of the absence of a good
vacuum environment in which to characterize and carefully control the sur-
face. The interaction of various environmental constituents with the solid
surface prevented such studies. However, with the advent of Sputnik at the
end of the 19503, a considerable amount of research resulted in the exten-
sive development of vacuum technology in the United States and elsewhere.
As a result of this development and the advances in vacuum technology, it
was possible in the early 1960’s to obtain clean vacuum systems which could
V
achieve pressures to 10-10 torr. At these pressures it is possible to obtain and
maintain atomically clean surfaces.
Shortly after the development of vacuum science and technology in the
early 1960’s, surface analytical tools became available for analyzing and
characterizing surfaces. Some of these tools include (1) LEED (low energy
electron diffraction), (2) field ion microscopy, (3) atom probe, (4) Auger
emission spectroscopy , and more recently (5) photospectroscopy.
With the combination of a good vacuum system and analytical surface
tools, it is now possible to characterize and analyze surfaces in tribological
systems very carefully. In earlier years it was taken for granted that when
one cleaned a solid surface with ordinary organic solvents the surface was,
in essence, clean. Today we know that is not the case. Even very carefully
cleaned surfaces inside a vacuum chamber, where such techniques as ion
bombardment are used to remove oxides and adsorbed layers, may not
necessarily be clean. The contaminant may not come from the environment
if the vacuum system is a good one with pressures of 10-10 torr or below.
They can come from within the bulk of the material and impart a surface
film to the solid. For example, small concentrations of impurities such as
sulfur and phosphorus in materials like iron, nickel, and copper can, with
mild heating or straining of the solid, migrate to the surface and con-
taminate an essentially clean surface.
In the 17th century, the philospher John Granville recognized the impor-
tance of understanding the fundamental nature of materials. He wrote,
“Iron seemeth a simple metal, but in its nature are many mysteries, and
men who bend to them, their minds shall, in arriving days, gather therefrom
greater profit, not to themselves alone but to all of mankind.’’ Since John
Granville wrote those words a considerable amount of research has gone
into understanding iron and iron chemistry. In the field of tribology, iron-
based alloys are one of the most commonly used materials. We are currently
trying to understand its surface; even elemental iron in a state of high purity
is a virtual chemical factory that can bring to its surface from the bulk sur-
face contaminants such as carbon and sulfur which can impart surface films
that alter markedly its adhesion, friction, and wear characteristics. Thus, it
has become apparent in recent years that to work with and understand the
nature of solid surfaces it is extremely important to have surface analytical
characterizing tools so that one knows and can fully appreciate those films
that are present on the surface and appreciate their role in tribological
behavior of materials in solid-state contact.
The objective of this text, then, is to introduce some recent advances in
the development of analytical surface tools for studying the tribological sur-
face by using a combination of the two factors referred to before: (1) a
vacuum system capable of holding and maintaining clean surfaces and (2)
analytical surface tools. Throughout this text, attempts are made to under-
stand the nature and character of solid surfaces that are used in tribological
systems. The primary emphasis is on the use of these tools as they relate to
tribology, both in situ type and post mortem analysis. The emphasis herein,
however, is on the tribological implications rather than on the instrumenta-
tion. The nature and the basic mechanism of operating the analytical tools
are reviewed very briefly in chapter 2.
VI
Contents
CHAPTER
I Introduction .................................................................... 1
.............................................................
Surface Geometry 2
.............................................................
Surface Chemistry 5
...............................................................
Bulk Chemistry 10
................................................................
Worked Layer 11
...............................................
Surface Effects in Tribology 13
.....................................................................
References 16
2 Surface Analytical Took ................................................ 17
..........................................................
Optical Techniques 17
................................
Surface Etching and Chemical Reaction 25
...........................
Mechanical Surface Topographical Devices 33
..................................................
Radioisotope Techniques 38
............................................................
X-ray Techniques 39
......................................
Transmission Electron Microscopy 50
............................................
Scanning Electron Microscopy 52
........................................................
Electron Microprobe 59
....................................
Auger Emission Spectroscopy (AES) 62
.............................
Low Energy Electron Diffraction (LEED) 73
............................
Appearance Potential Spectroscopy (APS) 78
..............................................
Ion Beam Analytical Sources 80
..................................................
Radiation Energy Sources 99
Electron Paramagnetic Resonance (EPR) and Nuclear
..........................................
Magnetic Resonance (NMR) 100
...........................................
Light Source Analytical Tools 101
...............................................
Infrared Spectroscopy (IR) 108
...........................................................
Surface Cleaning 109
Summary ..................................................................... 110
Appendix - Etchants ...................................................... 117
...................................................................
References 127
3 Solid Surfaces in the Perfect State ................................. 131
......................................................................
Bonding 133
...........................................................
Crystal Structure 138
........................................
Electronic Structure of Surfaces 143
............................................................
Surface Energies 146
Cleavage Planes ............................................................. 147
.........................................................
Cleavage Strengths 148
VII
Shear Strength Solids ...................................................... 149
Real Surfaces ................................................................ 152
Surface Defects ............................................................. 152
Substitutional or Interstitial Atoms .................................... 155
Dislocations ................................................................. 156
Stress Effects ................................................................ 164
Grain Boundaries and Their Energies .................................. 166
......................................................................
Ordering 169
........................................................
Surface Segregation 172
Environmental Interactions with Real Surfaces ..................... 182
References ................................................................... 194
4 TribologicalS urfaces .................................................... 197
Rough and Smooth Surfaces ............................................. 202
Atomic Nature of Tribological Surfaces .............................. 221
Metallurgical Effects ...................................................... 229
Chemical Nature of Surfaces ............................................ 238
References ................................................................... 243
5 Adhesion ...................................................................... 245
..........................................................
Cleavage of Solids 246
Surface Energy Effects .................................................... 247
.................................................
Alloy Segregation Effects 280
Metal-Semiconductor Contacts ......................................... 287
Surface Contaminant Effects ............................................ 288
Polymer Adhesion ......................................................... 294
Rubber Adhesion ........................................................... 307
References ................................................................... 313
4 Friction ......................................................................... 315
Physical Character of Surfaces .......................................... 324
Temperature Effects ....................................................... 344
......................................................
Metallurgical Effects 349
Orientation Effects ......................................................... 357
Similar Elements ............................................................ 364
Grain Boundary Effects ................................................... 366
Crystal Transformations .................................................. 369
Degree of Metallic Nature ................................................ 374
Effective Shear Strength .................................................. 374
Alloy Effects ................................................................ 378
Order-Disorder Reactips ................................................ 384
Chemistry of Friction ...................................................... 386
Composition of Surface Films ........................................... 408
Surface Substitution Reactions .......................................... 410
......
Role of Mechanical Surface Activity on Surface Chemistry 413
References ................................................................... 427
VIII
7 Wear. ............................................................................ 429
...................................................
Stress State in Materials 429
...............................................
Dislocation Concentration 432
.........................................
Effects of Surface-Active Films 434
.....................................................
Generation of Defects 437
.......................
Correlation of Strain and Dislocation Density 441
Degrees of Wear ............................................................ 444
...............................................................
Types of Wear 445
..............................................................
Adhesive Wear 446
..............................................................
Abrasive Wear 469
.............................................................
Corrosive Wear 485
................................................................
Erosive Wear 495
................................................................
Fatigue Wear 500
.........................................................................
Fretting 505
....................................................................
Cavitation 507
...................................................................
References 508
8 Lubrication of Solid Surfaces ........................................ 511
........................................................
Molecular Structure 514
...........................
Subsurface Effects on Lubricant Behavior 522
..........................................................
Surface Chemistry 524
....................................................
Environmental Effects 528
....................................................
Surface Concentration 531
...............
Environmental Effects on Lubricant Concentration 538
...........................
Mechanical Effects on Lubricant Behavior 542
...................................................................
References 552
9 Effect of Surface Films on the Mechanical
Behavior of Solid Surfaces ............................................ 553
..............................................................
Kramer Effect 3 4
...............................................................
Roscoe Effect 557
..................................................................
Joffe Effect 559
...........................................................
Rehbinder Effect 561
....................................
Summation of Surface Film Effects 563
...................................................................
References 566
I0 Solid Film Coatings ...................................................... 569
..................................
Graphite and Molybdenum Disulfide 573
........................................
Other Types of Solid Lubricants 577
Defining Solid Film Lubricants by Using Plasma Physics .........5 82
...................................................................
References 616
Author Index ................................................................ 619
Subject Index ................................................................ 623
IX