Project: Fake Golden Watch
Materials in industrial applications & Characterization of materials
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
2011-10-24
Lock
Link
Back
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Summary
In this project, three parts of a cheap watch was investigated, back, link and lock. After preparation
of the three samples their chemical composition was determined in SEM. The samples were etched
to be able to look at the microstructure in a light microscope. Then Vickers hardness tests were done
in main material and some of the layers in the coating.
The different layers of coating in both the link and the lock consist of Cu alloys attached through
electroplating. Main material in the lock consists of hot rolled Cu-Zn alloy with small grains and a
striped structure. Main material in the link is a cast Al-Zn alloy, with a dendritic alpha-beta
microstructure.
The back of the watch consists of 18-8 austenitic stainless steel.
2
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Table of Contents
Summary ................................................................................................................................................. 2
Introduction............................................................................................................................................. 4
Background.......................................................................................................................................... 4
Method ................................................................................................................................................ 4
SEM – Scanning Electron Microscope ............................................................................................. 4
Light microscopy.............................................................................................................................. 5
Difference between light microscopy and SEM .............................................................................. 5
Results ..................................................................................................................................................... 6
Back ..................................................................................................................................................... 6
Chemical composition and microstructure ..................................................................................... 6
Lock...................................................................................................................................................... 7
Chemical composition ..................................................................................................................... 7
Microstructure............................................................................................................................... 10
Link .................................................................................................................................................... 11
Chemical composition ................................................................................................................... 11
Microstructure............................................................................................................................... 13
Micro hardness .................................................................................................................................. 13
Metal coating technology...................................................................................................................... 14
Discussion .............................................................................................................................................. 15
Conclusion ............................................................................................................................................. 15
3
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Introduction
Background
In this project, a cheap watch was selected to be investigated. It was taken apart and three
interesting pieces were picked to be examined to determine the structure and composition.
Method
The watch was taken apart to be able to investigate the most interesting parts. The backside of the
clock, one of the links and the lock were selected. To be able to look at the pieces in the SEM,
Scanning Electron Microscope, the parts had to be conformed into samples. The information
received from the SEM contained data about the microstructure and the chemical composition.
When the composition was determined the appropriate etching medium was selected to be able to
look more closely at the microstructure in the regular microscope. From those pictures it was
possible to do further analysis of the watch and conclude the fabrication method for the different
parts. The hardness of the parts was examined to determine if the hardness varied in the different
layers.
SEM – Scanning Electron Microscope
The SEM uses electrons that are produced in a chamber and is focused in a beam by currents that
with the help of lenses are directed to the specimen that will be investigated. This procedure is done
in vacuum conditions to be able to look at the sample without oxides forming on the surface. When
the electrons reach the surface a number of things can happen. Either the electrons bounces back
from the surface, these are called backscattered electrons. The beam electrons can also excite Valens
electrons of the atoms in the sample which are then called secondary electrons. The secondary
electrons get a kinetic energy between 0-50eV. Sometimes if the energy of the beam is high enough
they can even ionize an atom by exciting one of the inner shell electrons. The excess energy can be
emitted like an Auger electron or be emitted like characteristic X-rays. Some of the electrons in the
beam travel straight through the sample, these are called transmitted electrons. The last alternative
is that they are simply absorbed by the sample.
The secondary electrons can also be produced by backscattering electrons that is hitting the walls
inside the chamber. Some of the secondary electrons can be obtained by using an Everhart-Thornley
detector, called E-T detector. A TTL-detector (“Through the Lens” detector) can also be used to study
the kinetic energy of the secondary electrons. The detectors give an image of the surface of the
specimen. The energy of the electron beam decides how much of the sample is being investigated;
the higher energy the deeper into the sample the beam excites electrons. There is also a possibility
to use more than one detector to get a more truthful picture of the sample. The image obtained in
the SEM will show the details that are angled towards the detector as brighter than the details
angled in the opposite direction. The resolution of the SEM depends on the wavelength of the
electrons and the electron-optical system that produce the scanning beam. It is also limited by the
interaction volume between the specimen and the beam. The resolution varies between 1-20nm
depending on the instrument. The magnification varies from 10 to 500 000 times. The depth of field
is very good in the SEM which means that the image will look almost like in 3D. It is also possible to
4
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
determine the chemical composition in the SEM with the help of EDS (Energy-dispersive X-ray
spectroscopy). The EDS obtain the X-rays that are emitted when the beam excites electrons of the
inner shells in the specimen’s atoms. The concept is that the different shells in the different elements
send out specific X-rays which allows the identification of specific elements and also how much of the
element that is present.
There are some problems that can occur when using the SEM. One example is charging of the
sample. There is also a problem concerning what electrons are obtained in the E-T detector. When
looking at the bulk material sometimes there can be a misleading image because a lot of the
secondary electrons never leave the material, their kinetic energy decreases on the way out. The
depth that can be examined is very shallow, only around a few nanometers.1 2
Light microscopy
Light microscopy is the most common and a standard method used to observe morphology of phases
that come from industrial processes involving phase transformation, plastic deformation and
annealing. The microstructure with grains and grain boundaries can be investigated. In a light
microscope the sample is illuminated with light that reflects on the surface of the sample. A linear
magnification of maximum 2000x and a resolution of 200 nanometers can be obtained in light
microscopy. The magnification is limited by the wavelength of the light, lens aberration and some
other factors.
To provide better images in a light microscope the sample is illuminated with light. Objectives with
different magnification make it able for the user to customize the magnification. Light microscopy is
used to observe the size and shape of the grains in single phase materials and in materials containing
more than one phase, as steel for example, the effects of deformation, micro cracking and heat
treatment is observed. Morphology and size of precipitates, compositional inhomogeneity, micro
porosity, thickness and structure of surface coatings, corrosion and also microstructure and defects
in welds is other structural features that can be observed in a light microscope.
Light microscopy requires carefully prepared specimens but is simple to use. To prepare a metal
surface metallographic techniques are used, that is grinding, polishing and etching, to reveal
microstructure constituents. For a given metal or alloy a number of etchants may work but they will
produce different results. 3
Difference between light microscopy and SEM
One difference is how deep you can look in to the surface of a material. In light microscopy it is only
possible to get a picture of the surface of the sample, but in SEM the depth is a few nanometers. It is
therefore possible for SEM to give information about what elements the material consists of. One
limit in light microscopy is that only visible light can be used. In SEM, sending particles with a higher
energy can change the penetration depth in the sample. Wavelength of these high-energy particles is
1
http://www.student.kau.se/kurstorg/files/s/C10B9B6B16513171A5uRSrBAFB67/sem1.pdf
http://www.student.kau.se/kurstorg/files/s/C10B9B6B16513171F5QtwK5F7008/sem2.pdf
3
http://www.student.kau.se/kurstorg/files/o/C10B9B6B15fff1727CwXFDF327F9/Optical%20microscopy.pdf
2
5
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
not visible and can therefore not be used in a light microscope, but in SEM the microscope itself
detects the particles and conclude the information about the sample.
Another difference is that light microscopy gives an image with approximately up to ten times higher
resolution than the SEM. Pictures from light microscopy is more suitable for investigation of
microstructure. These can be compared with other images of microstructure and standards to
determine for example fabrication methods.
Results
Back
Chemical composition and microstructure
Because of the chemical composition of Chromium ≈18% and Nickel ≈8%, the material is probably a
18-8 steel (Table 1). A picture taken during the SEM is presented in fig. 1. As seen in the picture the
back of the watch consists only of the main material.
Fig. 1. Back of watch in SEM
Table 1. Content in back of the watch in percent.
Spectrum
1
Fe
67,21
Cr
18,31
Ni
7,53
Mn
0,85
When looking at the backside in a microscope it shows that the material has porosities (Fig 2). After
etching the material, the picture in the microscope (Fig 3) was compared to standard SS 11 11 01.
6
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
The grain size turned out to be approximately a G12, which is smaller than 22,1 µm (=G8, the
smallest comparable picture). The microstructure was comparable to austenitic stainless steel, 304.
Because of the low price and quality of the watch, it was concluded that the backside probably had
been punched.
Fig 2. Back of watch viewed in microscope.
Fig 3. Etched back of watch.
Lock
Chemical composition
The chemical composition in the different layers is presented in table 2. The coating on the lock (Fig
4, Spectrum 1) constitutes of a mixture of elements, mostly copper. The gold is added to get the
beautiful appearance and trick the customer into believing it is an expensive golden watch.4 The
mixture of gold and palladium makes the surface of the watch harder. The next layer (Fig 4, Spectrum
2) constitutes only of Ni and Cu. The Cu has a good corrosion resistance and works as a kind of glue
4
http://www.copperinfo.co.uk/alloys/brass/downloads/117/117-section-5-how-to-make-it-in-brass.pdf
7
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
for the outer layer and the Ni also contributes to a harder surface. The white spots (Fig 4, Spectrum
6) contain approximately 80% Pb. The Pb could have gotten into the material during the mining of
copper ore or is added to improve the free cutting ability. The variation of percentage of the
different elements in the layers is presented in fig 5 and fig 6.
Fig 4. Different layers at the edge of the lock showed in SEM.
Lock
100
90
Cu
Zn
Au
Pb
Pd
Ni
Ti
Sn
O
80
Percent
70
60
50
40
30
20
10
0
0
2
4
Spectrum
6
Fig 5. Content of element in lock.
8
8
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Table 2. Content in the lock in percent.
Spectrum
1
2
3
4
5
6
7
Cu
42,48 90,05 79,37 91,22 84,03 9,63 50,56
Zn
10
0
3,42
0
3,4
7,55 39,35
Au
9,23
0
0
0
0
0
0
Pb
2,59
0
1,9
0
0,96 79,96 1,24
Pd
6,18
0
0
0
0
0
0
Ni
9,88 0,64 1,29
0
0
0
0
Ti
1,57
0
0
0
0
0
0
Sn
12,82
0
6,31
0
4,36
0
0
O
0
0
0
0
0
3,2
0
Looking at the lock in a microscope shows that the material has porosities (fig 7). After etching the
material, the picture in the microscope (fig 8) was compared to standard SS 11 11 01. The grain size
turned out to be approximately a G5, d=62, 5µm. The grains in the microstructure were not round,
more elongated, which probably means that rolling was used as fabrication method.
Fig 7. Layers of different materials in the edge of the lock.
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Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Fig 8. Etched lock. Shows microstructure.
Microstructure
The lock of the watch was made of a wrought, hot rolled, CuZn alloy. In the process of hot rolling,
metal is heated up to above recrystallization temperature. The material is rolled between a series of
rolls to reduce thickness, one over and one under, which will force the material to undergo plastic
deformation. The plastic deformation will cause the material to keep its form after the load is
removed. Generation, movements and storage of dislocations (defects in the crystal structure) cause
plastic deformation to proceed in the material. When the material is pressed together between the
rolls, shear stresses are induced and will force dislocations to move. When the material contains a lot
of dislocations they can stop each other’s movement. Dislocations in the material are a source to
internal stresses, which cause strain hardening.5
Before hot rolling, the microstructure of the cast slab is a eutectic structure containing dendrites
from a non-uniform cooling.6 The hot rolling transforms the dendritic structure of cuprous oxide into
a more “striped” microstructure with a lot of small grains. Because of the amount of Zn, 39%, it can
be concluded that the material consists of a mixture of alpha and beta phases, with the beta phase
containing more Zn than Cu.7 A dendritic material is hard and brittle, but after hot rolling, when
dendrites are exchanged for small grains, the material has a higher strength and ductility.8
5
http://books.google.com/books?id=EKBVPwCMI6cC&pg=PA92&lpg=PA92&dq=hot+rolling+dislocations&sourc
e=bl&ots=TgggZJIMBN&sig=t19myEhekFddT26_qcihoLVViSU&hl=sv&ei=uCGkToalB8zR4QTo3rTSBA&sa=X&oi=b
ook_result&ct=result&resnum=4&ved=0CDwQ6AEwAw#v=onepage&q=hot%20rolling%20dislocations&f=true
6
http://www.copper.org/resources/properties/microstructure/coppers.html
7
http://www.student.kau.se/kurstorg/files/l/C10B9B6B1689725FE3xsvG4CD7D1/Lecture%20Cu%20alloys_201
1.pdf
8
http://www.copperinfo.co.uk/alloys/brass/downloads/117/117-section-5-how-to-make-it-in-brass.pdf
10
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Link
Chemical composition
The second layer (Fig 10, Spectrum 2) contains Cu and Ni, which is called Nickel Silver. The variation
of the percentage of elements in the different layers is presented in fig 11 and fig 12. The first layer
(Fig 10, spectrum 1) consists of about the same amount Cu and Zn as seen in the coating on the lock
to get the same golden color.9
Fig 10. Layers of different material in edge of the link showed in SEM.
Link
Percent
100.00
Cu
90.00
Zn
80.00
Au
70.00
Pb
60.00
Pd
50.00
Ni
40.00
Ti
30.00
Sn
20.00
O
10.00
Al
0.00
S
0
2
4 Spectrum 6
8
10
Fig 11. Content of element in link.
9
http://www.copperinfo.co.uk/alloys/brass/downloads/117/117-section-5-how-to-make-it-in-brass.pdf
11
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Table 3. Content in the link in percent.
Spectrum
1
2
3
4
5
6
7
8
Cu
44,09 78,87 67,69 85,66 84,43 0,87
0
1,07
Zn
10,81
0
5,91
0
3,11 87,11 80,42 66,31
Au
6,64
0
0
0
0
0
0
0
Pb
3,22
0
2,62
0
0
0
0
0
Pd
1,87
0
0
0
0
0
0
0
Ni
6,84 3,78 1,51
0
0
0
0
0
Ti
0
0
0
0
0
0
0
0
Sn
14,15
0
8,09
0
0
0
0
0
O
0
0
0
0,9
1,64 2,33 1,49 2,44
Al
0
0
0
0
0
0,93 6,54 21,52
S
0
0
0
0
0
0
0
2,34
Ta
0,33
0
0
0
0
0
0
0
Fig 13 shows porosities in the material. After etching the material, fig. 14 was compared to standard
SS 11 11 01. The grain size turned out to be approximately a G10, which is smaller than d=22, 1 µm
(=G8, the smallest comparable picture). The microstructure in fig 14 shows round particles which
actually are dendrites seen in a cross section. This means that casting was used as fabrication
method.
Fig 13. Layers of different materials in the edge of the link.
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Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Fig 14. Etched link. Shows microstructure.
Microstructure
The links in the watch was made of an AlZn alloy that had been casted. The microstructure consists of
a mixture of eutectic material, slag and dendrites, which makes material hard but brittle. During the
casting the material is first heated above the melting temperature and then slowly cooled down.
When the material reaches solidifying temperature dendrites start to form and grow. The dendrites
start to form around the surface moving inwards because of the temperature difference on the
surface and inside the material.
Micro hardness
Since the layers in the coating of the lock and the link varied in size it was not possible to analyze all
of the layers since some of them were too small to be examined. The results from the hardness test
are presented in table 4.
Table 4. Results from the hardness test for the watch.
Part
Back, main material
Lock, 2nd layer (thick)
Lock, 4th layer (thick)
Lock, main material
Link, 2nd layer (thick)
Link, 3rd layer (thin)
Link, 4th layer (thick)
Link, main material
Spectrum
1
2
4
7
2
3
4
7
Vickers (HV)
320
287
323
173
297
354
108
106
The result for the back indicates that the stainless steel is austenitic when comparing the hardness
with other austenitic stainless steels.
13
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
Metal coating technology
After discussions and searching the web we concluded that the most probable way to coat the watch
is by using electroplating. Electroplating is an electrodeposition process for producing coatings of
metal or alloys by using an electric current. You use an electroplating unit, called electrolytic cell that
is containing of an electrolyte, an anode and a cathode with a current passing through. The material
that you want to coat will be the cathode and the coating material will be the anode. The electrolyte
is a fluid that enables the current to flow between the anode and the cathode. When applying the
electric current the positive ions will move from the anode to the cathode and the negatively
charged ions will move to the anode. The metallic ions that are positively charged will react with the
cathode and provide electrons to reduce those positively charged ions to metallic form which
enables the metal atoms to be deposited onto the surface of the cathode, in our case: the watch. Fig.
1. Shows an example of how the electroplating is done.
Fig. 1. Example of Electroplating with copper.
Before the electroplating the material needs to be prepared to get the coating to stick. This is done in
a number of steps consisting of surface cleaning, surface modification and rinsing. The electroplating
process can be accomplished in different ways depending on the size, shape or amount of material
being coated. In our case we believe it is either mass plating or inline plating because of the low price
and simplicity of the design and the ability to coat a lot of pieces at the same time. The electroplating
seems like the probable method for the coating due to the various materials you can use with this
process. You can coat with different alloys and also do multilayered coatings which, from our point of
view, seem suitable for the watch. This method is widely used for jewelry because of the ability to
14
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
perform a beautiful and smooth surface without any additional treatments, which make the
manufacturing cheaper and more effective. 10
Discussion
The copper is probably used because of its high corrosion resistance and its ability to work as a kind
of glue between the different layers of the coating. Copper is also good to use in jewelry because of
its good antibacterial properties. The nickel is probably used because of its ability to increase the
hardness of the coating and to avoid the copper to start “shining through”. You want the watch to
look golden as long as possible. The copper and zinc alloy, brass, is a good alternative because it can
look like gold and has good corrosion resistance. Gold and palladium are added as well, probably to
get a more genuine golden look and increase the hardness of the surface. There are many different
ways you could improve the quality and properties of the watch but then the price would increase
rapidly. The fabrication methods that were used are most likely the cheapest and simplest
alternatives. There is no warranty for a cheap watch so it does not need especially good mechanical
properties. As long as it looks nice for a while and does not fall apart immediately the customer is
satisfied. If there was a desire to improve the properties one example could be to get rid of the
porosities, which could be achieved by adding Mg to the cast. Another example would be to use the
same material for the lock but also have it solid solution strengthened.
The reason for having so many different layers in the coating is probably to get a surface that is as
smooth as possible without having to do a lot of fine grinding and polishing. It is probably cheaper to
use electroplating several times compared to different mechanical methods to get the same result.
The material in the lock is a lot harder than the material in the links because the lock needs to be
more resistant to wear. The hot rolling increases the strength in the lock. Other techniques could
make the material harder but there would be a risk of getting a more brittle material. The stainless
steel in the back of the watch is probably chosen because of the low price and accessibility. It can
also withstand corrosion, which is important in terms of resisting moisture forming between the skin
and the watch.
Because of the higher content of Ni in the 2nd layer of both lock and link compared to the 4th layer
in the lock and the 3rd layer in the link the assumption was that the hardness would be greater. This
was not obtained in the hardness test. The reason is probably because of the size of the layers, they
are very small and it was difficult to get a fair reading from these areas. Another limitation was time
which meant that we did not have time to do more than a couple of measurements in each layer.
Conclusion
Both lock and link contains a lot of copper in every layer of the coating because of its good corrosion
resistance, antibacterial property and function as glue. Instead of using a lot of gold, brass is used to
10
http://chem1.eng.wayne.edu/~yhuang/Papers/Book_Plating_ECHP.pdf
15
Project: Fake Golden Watch
Karlstad University ht11
Sofia Emanuelsson, Jessica Eriksson & Louise Ulfstad
get the golden color of the watch. The different layers are attached by using electroplating, to get a
smooth surface.
Main material in the lock, Cu-Zn alloy, is hot rolled. Its microstructure is an alpha-beta phase with
small grains in a “striped” structure. Main material in the link, Al-Zn alloy, is manufactured through
casting. The microstructure consists of a eutectic material, slag and dendrites.
The back is an 18-8 austenitic stainless steel, because it is cheap and has a high corrosion resistance.
16