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Plastic replicas for optical and scanning electron microscopy
Wear, 29 ( 1974) 27 l-274 0 Elsevier Sequoia S.A., Lausanne
SHORT
271 - Printed
in The Netherlands
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Plastic replicas for optical and scanning electron microscopy
S. ANDERSSON Tribology Group, Department of Machine Elements, Royal Institute of Technology, Stockholm (Sweden) (Received
December
31, 1973; in final form March
12, 1974)
Plastic replicas easily and quickly made used in conjunction with optical and scanning election microscopy offer a non-destructive method of examining the surface condition and surface damage of machine components. Introduction
Reliable and quick non-destructive test methods are in great demand. Scott’ has described the role of replicas for optical and transmission electron microscopical investigation of bearing failures. The scanning electron microscope, because of its large depth of focus at high magnification, is now used in tribology. However, specimens have to be conductive and, if not, must be coated with a very thin conductive layer. Plastic is the most common replica material and after vacuum deposition of a conductive coating may be examined in the scanning electron microscope. They may also be examined in the optical microscope.
Fig. 1. Scanning
electron
micrograph
of
(a) a test specimen,(b) a replicaof
the test specimen.
( x 600)
272
SHORT
COMMUNICATIONS
Plastic replicas
Acetyl cellulose film, which is soluble in acetone is a suitable replica material. The replication procedure is: clean the surface and cut a piece of the plastic film, soften one side of the plastic with acetone (about 30 s); place the plastic on the surface and allow to remain for a few minutes; loosen and check the replica; remove the replica and glue onto a specimen which fits into the microscope; coat the replica in uacuo with a conductive layer. Figure 1, (a), the real surface and (b), the replica shows that there is good correlation between the actual surface and the replica.
Fig. 2. Scanning electron (7 slip direction) ( x 200)
micrograph
of a replica
of a ground
gear
tooth
llank
after
running-in.
Air bubbles must be avoided. These can be prevented by the use of small pieces of plastic and careful cleaning of the surfaces of grease and oil. Replicas of rough surfaces must be carefully assessed in case of tearing on removal as shown at A in Fig. 2. Application Plastic replicas are suitable for the investigation of surfaces, which cannot be examined directly in the microscope, also for the investigation of transient processes and service equipment without causing serious interruption. The initial wear of gear tooth flanks working under normal conditions is slight but increases with increasing load and the changes may be studied by microscopic examination of the surfaces or their replicas. The wear is dependent on factors such as surface roughness, speed and lubrication and since the knowledge of the influence of these factors is well understood it is possible to estimate the
SHORT
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213
Fig. 3. Scanning electron micrographs of replicas of a shaved test gear tooth flank during running-in, (a) before running-in, (b) after 0.3 x lo6 rev. at (r,=400 N/mm’, (c) after further 0.3 x 10b rev. at uu N 500 N/mm3. (r slip direction) ( x 200)
working conditions of gears by microscopic examination of selected flanks. The micrographs in Fig. 3 show changes of a shaved tooth flank during running-in at different loads. An understanding of the actual working conditions is a useful aid when estimating the probability of failure of the rubbing surfaces and selection of the surface area to be examined by the replica technique. By replicating at constant intervals fatigue crack and fatigue pit formation may be discovered at an early stage, Fig. 4, to prevent troublesome and costly breakdowns. Plastic replicas coated by a conductive layer may be examined both in optical and scanning electron
274
Fig. 4. Scanning (1 slip direction)
SHORT
electron ( x 200)
micrograph
of a replica
of a tooth
flank which
COMMUNICATIONS
has worked
at a high load.
microscopes. The replica may first be examined at low magnification by an optical microscope to get an overall view of the amount of wear and areas of interest may be examined by a scanning electron microscope. Conclusions Replicas provide a useful non-destructive method of studying surfaces in both optical and scanning electron microscopes; correlation between the plastic replica and the original surface is good. The use ofreplicas is suitable for the investigation of transient processes such as running-in and for studying machine components in service.
REFERENCES 1 D. Scott, Bearing failures diagnosis and investigation, Wear, 25 (1973) 199-213. 2 S. Andersson, Avtryck-ett hjllpmedel fiir iikad anvlndning av SEM, SEM meeting Center, Royal Inst. Technol. Stockholm, 1973.
at Materials
SHORT
271 - Printed
in The Netherlands
COMMUNICATION
Plastic replicas for optical and scanning electron microscopy
S. ANDERSSON Tribology Group, Department of Machine Elements, Royal Institute of Technology, Stockholm (Sweden) (Received
December
31, 1973; in final form March
12, 1974)
Plastic replicas easily and quickly made used in conjunction with optical and scanning election microscopy offer a non-destructive method of examining the surface condition and surface damage of machine components. Introduction
Reliable and quick non-destructive test methods are in great demand. Scott’ has described the role of replicas for optical and transmission electron microscopical investigation of bearing failures. The scanning electron microscope, because of its large depth of focus at high magnification, is now used in tribology. However, specimens have to be conductive and, if not, must be coated with a very thin conductive layer. Plastic is the most common replica material and after vacuum deposition of a conductive coating may be examined in the scanning electron microscope. They may also be examined in the optical microscope.
Fig. 1. Scanning
electron
micrograph
of
(a) a test specimen,(b) a replicaof
the test specimen.
( x 600)
272
SHORT
COMMUNICATIONS
Plastic replicas
Acetyl cellulose film, which is soluble in acetone is a suitable replica material. The replication procedure is: clean the surface and cut a piece of the plastic film, soften one side of the plastic with acetone (about 30 s); place the plastic on the surface and allow to remain for a few minutes; loosen and check the replica; remove the replica and glue onto a specimen which fits into the microscope; coat the replica in uacuo with a conductive layer. Figure 1, (a), the real surface and (b), the replica shows that there is good correlation between the actual surface and the replica.
Fig. 2. Scanning electron (7 slip direction) ( x 200)
micrograph
of a replica
of a ground
gear
tooth
llank
after
running-in.
Air bubbles must be avoided. These can be prevented by the use of small pieces of plastic and careful cleaning of the surfaces of grease and oil. Replicas of rough surfaces must be carefully assessed in case of tearing on removal as shown at A in Fig. 2. Application Plastic replicas are suitable for the investigation of surfaces, which cannot be examined directly in the microscope, also for the investigation of transient processes and service equipment without causing serious interruption. The initial wear of gear tooth flanks working under normal conditions is slight but increases with increasing load and the changes may be studied by microscopic examination of the surfaces or their replicas. The wear is dependent on factors such as surface roughness, speed and lubrication and since the knowledge of the influence of these factors is well understood it is possible to estimate the
SHORT
COMMUNICATIONS
213
Fig. 3. Scanning electron micrographs of replicas of a shaved test gear tooth flank during running-in, (a) before running-in, (b) after 0.3 x lo6 rev. at (r,=400 N/mm’, (c) after further 0.3 x 10b rev. at uu N 500 N/mm3. (r slip direction) ( x 200)
working conditions of gears by microscopic examination of selected flanks. The micrographs in Fig. 3 show changes of a shaved tooth flank during running-in at different loads. An understanding of the actual working conditions is a useful aid when estimating the probability of failure of the rubbing surfaces and selection of the surface area to be examined by the replica technique. By replicating at constant intervals fatigue crack and fatigue pit formation may be discovered at an early stage, Fig. 4, to prevent troublesome and costly breakdowns. Plastic replicas coated by a conductive layer may be examined both in optical and scanning electron
274
Fig. 4. Scanning (1 slip direction)
SHORT
electron ( x 200)
micrograph
of a replica
of a tooth
flank which
COMMUNICATIONS
has worked
at a high load.
microscopes. The replica may first be examined at low magnification by an optical microscope to get an overall view of the amount of wear and areas of interest may be examined by a scanning electron microscope. Conclusions Replicas provide a useful non-destructive method of studying surfaces in both optical and scanning electron microscopes; correlation between the plastic replica and the original surface is good. The use ofreplicas is suitable for the investigation of transient processes such as running-in and for studying machine components in service.
REFERENCES 1 D. Scott, Bearing failures diagnosis and investigation, Wear, 25 (1973) 199-213. 2 S. Andersson, Avtryck-ett hjllpmedel fiir iikad anvlndning av SEM, SEM meeting Center, Royal Inst. Technol. Stockholm, 1973.
at Materials