Small friction and wear apparatus built directly into scanning-electron-microscope provides both dynamic observation and microscopic view of wear process. Friction and wear tests conducted using this system have indicated that considerable information can readily be gained

Brainard, W. A.

Buckley, D. H.

English

NASA Technical Reports Server

June 1975	 B75-10064 
•	 NASA TECH BRIEF 
Lewis Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service. Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Scanning-Electron-Microscope Used 
in Real-Time Study of Friction and Wear 
. 
.
The Problem: 
The wear of solid surfaces in sliding contact begins 
with contact between the high points or asperities on each 
of these surfaces. The macroscopic wear behavior is really 
a summation of microscope events. In addition, the wear 
process is a dynamic process in the sense that mechanisms 
change with load, speed and time so that static or 
post-testing examination of work surfaces is not adequate 
for many cases. The need, therefore, is for a method or 
methods of studying friction and wear phenomena at the 
microscopic level: and under dynamic conditions. 
The Solution: 
A small friction and wear apparatus built directly into 
a scanning-electron-microscope (SEM) to provide both 
dynamic observation and a microscopic view of the wear 
process. 
How It's Done: 
The friction and wear experiments were conducted in 
the vacuum chamber of the SEM. The SEM is a field 
emission electron source type which provides for real time 
viewing on a closed circuit television system at 15 
complete frames per second. 
The friction and wear apparatus used is shown sche-
matically in the figure. A disk specimen 1.9 cm (0.75 in) 
in diameter is mounted on an adapter to the rotary 
specimen feedthrough. The surface of the disk is inclined 
at approximately 830 with respect to the electron beam to 
permit the interface to be viewed from a near side view. A 
variable speed electric motor and gear train provides 
rotation of the disk from 0.1 to 10 rpm. The rotation can 
either be clockwise or counterclockwise to provide for 
observation of either the prow or the wake of the rider 
disk contact. In addition, a side view of the wearing 
process can be observed, without, however, the capability 
of friction force measurements. 
The rider specimen is 0.1 cm (0.039 in) in diameter 
with an 0.05 cm (0.02 in) radius on the end. A 20° taper 
is machined on the shank down to the radius in order to 
reduce the shadowing of the interface.
Dr 
Detailed drawing of friction appratus mounted on scanning electron microscope. 
The rider is mounted in an arm which can be moved in 
and out as well as up and down and laterally by means of 
a bellows and gimbal system. The gimbal system is a 
precision optical orientor mounted on a translational 
stage. The stage and the optical orientor are micrometer 
controlled allowing very precise positioning of the rider 
on the disk under the scanning beam. 
The arm in Which the rider is mounted contains two 
flex bands of beryllium-copper on which strain gages are 
attached. One band mounted parallel to the disk surface is 
used to measure the normal load applied to the contact. 
The other band and strain gage are mounted perpendicular 
to the disk surface and monitor the friction force. In 
addition, another strain gage is mounted on the bottom of 
(continued overleaf) 
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the load band and can measure the force of adhesion 
between the rider and disk. The normal loading is 
accomplished by magnets mounted on the optical orientor 
ring which pull the arm downward to the disk surface. 
The load sensing gage output is amplified and displayed 
on a digital millivolt meter which, with suitable calibra-
tion, provides for a direct reading of the load being 
applied. The friction force gage is read out either on a 
strip chart recorder or oscilloscope to provide for the 
observation of the friction trace which is more transient in 
nature. 
The entire friction test is viewed on the television 
monitor of the SEM and the video signal is recorded on 
video tape, together with audio comments. The tape can 
be played back in slow motion and stop action to 
facilitate interpretation. In addition, kinescopic motion 
pictures can readily be made from the video tape. 
The addition of a friction and wear apparatus to the 
scanning-electron-microscope with real time scanning pro-
vides for in situ experimentation and the observation of 
the friction and wear process at a very basic level. The 
system developed for this purpose provides the following: 
1. Precise specimen positioning necessary for keeping 
the contact region in the field of view at increased 
magnifications, 
2. A low-angle view, relative to the disk surface, of the 
actual sliding interface, 
3. SEM viewing of the prow, the wake, or side of the 
rider-disk contact region with continuous friction meas-
urements in prow or wake positions, 
4. A loading system providing for continuous loading 
from 1 to 75 grams force, 
5. A continuously variable speed control from 0.1 to 
10 rpm, which, depending on the radial distance of the 
contact from the disk center, provides surface sliding 
speeds from 0.94 to 0.003 cm (0.37 to 0.001 in) per 
second, and 
6. Dynamic data recording of visual information on 
video tape.
Friction and wear tests conducted using this system 
have indicated that considerable information can readily 
be gained. When used in conjunction with a dispersive 
x-ray analyzer, the following types of information are 
observable: 
1. The friction coefficient and the correlation of the 
variation with the actual wear process at any point in real 
time.
2. The type of wear, such as adhesive or abrasive wear, 
and changes in wear behavior with time, speed, or load, 
3. Identification of the primary wearing surface and 
source of wear particles, 
4. The size, shape, distribution, and agglomeration 
characteristics of the wear particles and their influence on 
the wearing process, and 
5. Metallic transfer between the sliding surfaces. 
Notes: 
1. Further information is available in the following 
report: 
NASA TN-D-7700 (N74-25975), Dynamic-
Scanning-Electron-Microscope Study of Friction 
and Wear 
Copies may be obtained at cost from: 
Aerospace Research Applications Center 
Indiana University 
400 East Seventh Street 
Bloomington, Indiana 47401 
Telephone: 812-337-7833 
Reference: B75-10064 
2. Specific technical questions may be directed to: 
Technology Utilization Officer 
Lewis Research Center 
21000 Brookpark Road 
Cleveland, Ohio 44135 
Reference: B75-10064 
Patent Status: 
NASA has decided not to apply for a patent. 
Source: W.A. Brainard and D.H. Buckley 
Lewis Research Center
(LEW-1 2448) 
B75-10064	 Category 06


Scanning-electron-microscope used in real-time study of friction and wear

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