Honors Program Thesis Proposal
Magnetostriction of Nickel and
Related Material Properties
Author: Andy Fox
Advisor: David Morrison
March 7, 2005
Abstract
Little is known about the magnetic properties of ultra fine grain materials. One of
those properties is magnetostriction, or strain induced by magnetization in ferromagnetic
materials. Some applications of magnetostrictive materials are their use in sensors and
actuators. Also, magnetostriction has recently been identified as the cause of the
mechanical response characteristics in the cyclic plasticity of nickel. If more fully
understood, the magnetic properties resulting in these mechanical response characteristics
could be used to test the integrity of a structure and examine it for damage or fatigue. The
research proposed will be done to investigate and determine the magnetostrictive and
magnetic induction responses of ultra fine grain nickel.
Four samples of nickel have been prepared by different processes. Ultra fine grain
nickel was produced by electrodeposition while other samples were taken from Ni-270
cold drawn stock and annealed at varying temperatures and for varying lengths of time.
Preliminary tests have been done by placing the specimens in a solenoid and measuring
the magnetostrictive and magnetic induction responses with an extensometer and
gaussmeter respectively. Hardness measurements were also taken using a Vickers
Hardness tester.
The preliminary tests show that processes which manufacture smaller grain size
nickels produced hard magnetic materials that have low saturation magnetization, high
remnant magnetization and high coercive force. However, little correlation was found
between grain size and the magnetostrictive response in nickel. Therefore, a more
accurate method of measuring the magnetostrictive response is needed to better
determine the correlation with grain size.
Further investigation is proposed in which Transition Electron Microscope (TEM)
specimens will be examined for a better understanding of the grain structures and
dislocations. A more accurate way of measuring the magnetostrictive response will be
developed. The magnetic induction response will also be tested with a calibrated
gaussmeter to obtain more accurate results. The magnetic induction response during
reverse magnetostriction, or magnetization induced by strain, will also be investigated
and determined.
Introduction
Advances have recently been made in the development of processes for producing
metals with very small grain sizes. For example, large samples of ultra fine grain metals
can be produced by electrodeposition at a very low cost. These samples have many
favorable properties such as no residual porosity, long fatigue life, and exceptionally high
strength and hardness [3-6, 9].
However, little is known about the magnetic properties of ultra fine grain
materials. One such magnetic property of ferromagnetic materials is magnetostriction, or
strain induced by magnetization [7, 12]. Magnetostrictive materials can be used in
various applications such as in sensors and in actuators. Also, magnetostriction has
recently been identified as the cause of the mechanical response characteristics in the
cyclic plasticity of nickel [1]. This is shown below in Figure 1.
Figure 1: Shown above are selected axial stress vs. axial plastic strain responses of a
nickel single crystal specimen. The test occurred without a magnetic field and had a
nominally constant plastic strain amplitude of 0.00005 [2].
Magnetostriction and its related magnetic properties have major implications in
the fatigue properties of ferromagnetic materials such as iron, cobalt, and nickel that are
yet to be fully understood [6, 8-11]. The relationship between a ferromagnetic material’s
magnetic properties, such as magnetostriction, and mechanical properties, such as cyclic
plasticity, are hoped to be correlated with the purpose of testing the structural integrity of
a material or structure. If the correlation were known and fully understood, one would be
able to determine a material’s mechanical properties such as fatigue life by testing for its
magnetic properties. This would result in a way to test the integrity of a structure and
look for damage or fatigue within the material.
Methods
Microstructure Examination:
Nickel specimens have been produced for use in the experiments. Ultra fine grain
nickel, as well as nickels with varying grain sizes have been processed for comparison.
The ultra fine grain nickel was grown by electrodeposition and will be called the
“Electrodeposited” specimen. A sample of Ni-270 cold drawn stock was left as received
and will be called the “As Received” specimen. Two samples from the same Ni-270 cold
drawn stock were also annealed in a vacuum furnace, one at 500o C for 3 hours and the
other at 1000o C for 4 hours. The sample annealed at 500o C for 3 hours will be called the
“Fine Grain” specimen, and the sample annealed at 1000o C for 4 hours will be called the
“Coarse Grain” specimen.
Each of the specimen’s grain structure has been examined to correlate the
resulting grain size from material processing with the magnetostrictive and magnetic
induction response. Samples of the specimens were mounted in epoxy and polished on a
grinding wheel to 800 grit. They were further polished using diamond compound and
micropolish to 0.05 micron micropolish. Using 25% nitric acid, 25% acetic acid, and
50% H2O the specimens were etched for approximately 20 seconds. After etching the
specimens, the grain structure becomes visible using an optical microscope. A digital
camera was used to capture images of the grain structures.
The polished specimens were then used to take hardness measurements. A Leco
M-400 Hardness Tester was used to take Vickers hardness readings. The measurements
were taken across the specimens working out from the center.
Also proposed is the examination of the specimens using a Transition Electron
Microscope (TEM). TEM specimens must first be produced to examine the
microstructure. The specimens are sliced into 1 mm slabs which are glued to a solid
block. The slabs are then ground until they are 70 micrometers thick. They are then core
drilled in which 3 mm diameter cores are drilled out of the slabs. These TEM specimens
are then thinned until they are several micrometers thick. They are then ready to be
examined using the TEM. These TEM specimens will further the understanding of the
grain structures and dislocations within the specimens.
Magnetostriction Tests:
Fatigue specimens with the same properties as the four produced specimens were
used in the magnetostriction tests. These experiments were done by placing a solenoid on
each end of the specimen, 3.5 cm apart, and measuring the magnetostriction in the gauge
section with an extensometer. The solenoids were made with 30 gage copper magnet wire
wrapped around sewing bobbins and had 300 turns each. The solenoids and specimen
were cooled by a small fan which was run between tests.
To acquire the data from the tests in real time, a LabVIEW virtual instrument was
constructed. This virtual instrument used a BNC-2120 to acquire the voltage across a
resistor in the solenoid circuit and the strain signal from the extensometer. It then used
input values from the user such as the applied gain on the strain signal and the resistor
value that the voltage was measured across, to give readouts of the applied current and
the microstrain value in real time. A large graph was also used to plot the strain vs. the
applied current during the experiments.
During the tests, a Buehler Electromet Power Source connected to the solenoid
was ramped up to approximately 4 amps and data was collected. Five tests were run in
succession for each specimen with approximately 3 minutes between for cooling the
solenoids.
There were two main problems with the magnetostriction tests that hinder the
reliability of the data collected. The first problem is the solenoids used to create the
magnetic field. The two small solenoids on either end of the specimens made it
impossible to calculate the actual applied magnetic field. Only the applied current was
known. The solenoids were also made out of high gage magnet wire that became
extremely hot during the tests. As stated before, this heat caused thermal expansion in the
specimens. The second problem was the resistor used to measure voltage. It was a 1 ohm
10 watt resistor. The power that was applied was much higher and therefore the resistor
also became extremely hot. As the resistor’s temperature increased, its resistance also
may have increased, decreasing the accuracy of the applied current values. This could
have had a large effect on the magnetostriction slopes that were calculated.
The magnetostriction experiments need a way to apply the magnetic field that will
reduce the thermal effects and allow the user to calculate the applied field strength. Also,
many resistors placed in parallel rather than a single resistor would help to reduce heat
making the voltage readings more accurate. Solutions to these problems are currently
being investigated.
Magnetic Induction Tests:
The magnetic induction tests were done by placing the processed specimens in a
solenoid and measuring the magnetic induction with a Bell Model 620 Gaussmeter. The
gaussmeter was not calibrated and therefore only a unit value for the magnetic induction
was known. The solenoid was made with 22 gage copper magnet wire, had a length of
0.073 m, and had 445 turns. The gaussmeter probe was placed against the specimen
inside the solenoid. A double pole double throw switch was attached to the circuit to
quickly change the direction of the applied magnetic field. Ten 10 ohm, 5 watt resistors
were attached in parallel to reduce the current through each of them and the voltage was
measured across these resistors. A small fan was once again used to cool the solenoid and
the resistors.
Another LabVIEW virtual instrument was constructed for these tests. The BNC2120 was used to acquire the voltage across the resistors and the signal from the
gaussmeter. The virtual instrument then used input values from the user such as the
number of turns and length of the solenoid, the resistance that the voltage is measured
across, and the full scale range of the gaussmeter to calculate the applied magnetic field
and its resulting magnetic induction. These values were then plotted on a graph during
the test for the user to see.
For easy placement and removal from the solenoid, wood toothpicks were glued
to the ends of the cylindrical specimens which are shown below in Figure 2. These
specimens were used in the magnetic induction tests.
Figure 2: Shown above are the specimens used in the magnetic induction tests. The
specimens shown from left to right are: electrodeposited, as received, fine grain, and
coarse grain.
During the tests, the same Buehler Electromet Power Source used in the
magnetostriction tests was used to ramp the solenoid current up and down. The current
was ramped up and down, the switch was thrown to change direction and the current was
ramped up and down again. This procedure was done twice successively during each test.
Each of the specimens were tested only once.
There were two problems with the magnetic induction tests. First, the gaussmeter
was not calibrated and the actual values of the induction readings were therefore
unknown. Second, the solenoid was wrapped unevenly. A longer solenoid with more
wraps would help to alleviate this problem.
The magnetic induction experiments need a gaussmeter that is calibrated allowing
the user to know the values of the induction readings. A longer more evenly wrapped
solenoid would also make the applied field strength more accurate. Solutions to these
problems are currently being investigated.
Reverse Magnetostriction Tests:
Reverse magnetostriction is defined as magnetization induced by strain. It is
proposed that the nickel fatigue test specimens be used to define the reverse
magnetostrictive response. The specimens will be placed in the fatigue tester and
strained. A gaussmeter will then be used to measure the resulting magnetization within
the specimens. The gaussmeter probe will be placed next to the specimens and will read
the magnetization and send a signal to a LabVIEW Virtual Instrument that will record the
gaussmeter signal, and the signal from the fatigue tester simultaneously.
To obtain accurate results the gaussmeter needs to be accurate and calibrated. It is
currently being learned how to calibrate the current gaussmeter available, the Bell Model
620 Gaussmeter. The Mechanical and Aeronautical Engineering Department is also
exploring the possibility of buying a new gaussmeter that would enable accurate
readings.
LabVIEW Function Generators:
A LabVIEW virtual instrument is proposed to be developed for the
electrodeposition process. This virtual instrument will replace two function generators
and an oscilloscope that are currently being used to generate and read the plating signal.
The current function generators and oscilloscope are difficult to read and operate. The
development of a virtual instrument that will replace these will greatly simplify the
process and make it more user friendly.
Preliminary Results
Shown below in Figures 3-6 are pictures of the microstructures of the four
specimens that have been examined. These specimens were produced and pictures were
taken by the process described previously.
Electrodeposited Micrograph
Figure 3: Shown above is the grain structure of the ultra fine grain Electrodeposited
specimen. Each dash on the scale represents 10 micrometers.
As can be seen in Figure 3, the grain size for the electrodeposited sample is
extremely small and can not be seen with an optical microscope. The band running down
the center of the micrograph was created by stopping and restarting the deposition.
As Received Micrograph
Figure 4: Shown above is the grain structure of the As Received specimen. Each dash on
the scale represents 10 micrometers.
Figure 4 shows that the grains of the as received Ni-270 cold drawn stock
specimen are much larger than those of the electrodeposited specimen.
Fine Grain Micrograph
Figure 5: Shown above is the grain structure of the Fine Grain specimen. Each dash on
the scale represents 10 micrometers.
The grain size of the fine grain specimen shown in Figure 5 is larger than that of
the as received specimen. The annealing process creates grain growth within the
specimen which increases the grain size and also, as will be seen, decreases its hardness.
Coarse Grain Micrograph
Figure 6: Shown above is the grain structure of the Coarse Grain specimen. Each dash on
the scale represents 10 micrometers.
Annealing the specimen for a longer period of time creates further grain growth.
The grain size in the coarse grain specimen, shown in Figure 6, is much larger still.
The hardness measurements that were described previously are shown below in
Figure 7.
Hardness Measurements
500.0
450.0
400.0
Vickers Hardness
350.0
As Received
Fine Grain
Coarse Grain
Electrodeposited
300.0
250.0
200.0
150.0
100.0
50.0
0.0
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Distance from Center (mm)
Figure 7: Shown above are the Vickers hardness readings for the electrodeposited, as
received, fine grain, and coarse grain specimens.
It can be seen that the hardness decreases with increasing grain size. The
electrodeposited material is extremely hard while the annealed materials are much softer.
The data also shows that the greater annealing temperature and time given to the coarse
grain specimen did not decrease its hardness any more than the fine grain specimen.
There is also a trend across the specimens in which the hardness readings decrease as the
distance from the center increases. This occurs because there is less surrounding material
to resist the indenter as the distance from the center increases. The hardness reading at the
center of the electrodeposited specimen is extremely low because of the wire that the
material was plated on.
There is a jump in the electrodeposited readings at 2.0 mm from the center. This
is the first reading past the band that can be seen in Figure 3, which is after the plating
was restarted. The two highest readings on the electrodeposited specimen took place in
spots where the grain size was visibly smaller using 40 x magnifications.
Shown below in Figures 8-12 are the magnetostriction responses of the
electrodeposited, as received, fine grain, coarse grain, and single crystal specimens
respectively.
Electrodeposited Magnetostriction Trial #2
0.00
0
0.5
1
1.5
2
2.5
3
3.5
4
-5.00
Microstrain
-10.00
-15.00
Ramp up
Ramp down
-20.00
-25.00
-30.00
-35.00
Applied Current (A)
Figure 8: Shown above is a plot of the second electrodeposited magnetostriction test.
The electrodeposited specimen above shows a magnetostriction saturation value
of -32.0 microstrain and a slope of -31 microstrain/amps at 0.4 amps of applied current.
There is a slight hysteresis but the strain value at the beginning and the end of the test are
the same. This could be accounted for by the slight overall thermal expansion throughout
the test.
As Received Magnetostriction Trial #2
0.00
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Microstrain
-5.00
-10.00
Ramp up
Ramp down
-15.00
-20.00
-25.00
Applied Current (A)
Figure 9: Shown above is a plot of the second as received magnetostriction test.
The as received specimen above does not appear to entirely saturate but shows a
magnetostriction saturation value approaching -22.0 microstrain and a slope of -18.8
microstrain/amps at 0.4 amps of applied current. There appears to be more hysteresis than
then electrodeposited specimen, but once again the strain value at the beginning and the
end of the test are similar.
Fine Grain Magnetostriction Trial #2
5.00
0.00
0
0.5
1
1.5
2
2.5
3
3.5
4
Microstrain
-5.00
-10.00
Series1
Series2
-15.00
-20.00
-25.00
-30.00
Applied Current (A)
Figure 10: Shown above is a plot of the second fine grain magnetostriction test.
The fine grain specimen above shows a magnetostriction saturation value of -28.0
microstrain and a slope of -48.8 microstrain/amps at 0.4 amps of applied current. There is
less hysteresis than the electrodeposited specimen and once again the strain value at the
beginning and end of the test are similar.
Coarse Grain Magnetostriction Trial #2
0.00
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
4
-5.00
Microstrain
-10.00
-15.00
Series1
Series2
-20.00
-25.00
-30.00
-35.00
-40.00
Applied Current (A)
Figure 11: Shown above is a plot of the second coarse grain magnetostriction test.
The coarse grain specimen above shows a magnetostriction saturation value of 36.0 microstrain and a slope of -79.1 microstrain/amps at 0.4 amps of applied current.
There is less hysteresis than the fine grain specimen and the strain values at the beginning
and end of the test are once again similar.
Single Crystal Magnetostriction Trial #2
5.00
0.00
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Microstrain
-5.00
-10.00
Series1
Series2
-15.00
-20.00
-25.00
-30.00
-35.00
Applied Current (A)
Figure 12: Shown above is a plot of the second single crystal magnetostriction test.
A nickel single crystal specimen with a [123] orientation was also tested. Figure
16 shows a magnetostriction saturation value of -29.5 microstrain and a slope of -49.6
microstrain/amps at 0.4 amps of applied current. There is no hysteresis and the strain
value at the end of the test is slightly more than the value at the beginning but can be
accounted for by thermal expansion.
Figures 13-16 show the magnetic induction response for the electrodeposited, as
received, fine grain, and course grain specimens respectively.
Electrodeposited μM vs. H
40
30
Magnetization; μM
20
10
0
-100000 -80000
-60000
-40000
-20000
0
20000
40000
60000
80000
100000
-10
-20
-30
-40
Applied Magnetic Field; H (A/m)
Figure 13: Shown above is the plot of M vs. H for the electrodeposited specimen. It has
a saturation value of 35, permeability at coercion of 0.00120, remnance magnetization of
7.8 and a coercive force of 6800 A/m.
As Received μM vs. H
60
Magnetization; μM
40
20
0
-100000
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
100000
-20
-40
-60
Applied Magnetic Field; H (A/m)
Figure 14: Shown above is the plot of M vs. H for the as received specimen. It has a
saturation value of 50, permeability at coercion of 0.00163, remnance magnetization of
5.3 and a coercive force of 3300 A/m.
Fine Grain μM vs. H
60
Magnetization; μM
40
20
0
-100000 -80000
-60000
-40000
-20000
0
20000
40000
60000
80000
100000
-20
-40
-60
Applied Magnetic Field; H (A/m)
Figure 15: Shown above is the plot of M vs. H for the fine grain specimen. It has a
saturation value of 57, permeability at coercion of 0.00175, remnance magnetization of
0.0 and a coercive force of 0 A/m.
Coarse Grain μM vs H
60
Magnetization; μM
40
20
0
-100000
-80000
-60000
-40000
-20000
0
20000
40000
60000
80000
100000
-20
-40
-60
Applied Magnetic Field; H (A/m)
Figure 16: Shown above is the plot of M vs. H for the coarse grain specimen. It has a
saturation value of 56, permeability at coercion of 0.00166, remnance magnetization of
0.0 and a coercive force of 0 A/m.
The magnetic induction tests show that as the grain size of the material increases,
the material becomes more magnetically soft, which means that it is more easily
magnetized and demagnetized. As the grain size increased, the hysteresis loop of the
M vs. H plot became narrower, which is also a characteristic of soft magnetic materials.
The electrodeposited and as received specimens were harder magnetic materials than the
annealed specimens, meaning they were more difficult to magnetize and demagnetize.
From the preliminary results, the magnetostriction tests show no correlation
between grain size and the magnetostrain saturation values. There is also no correlation
between grain size and the slope of the magnetostrictive response. It was also found from
the magnetic induction tests that the smaller grain size nickels are harder magnetic
materials. They have low saturation magnetization and high remnant magnetization and
coercive force. The larger grain size annealed specimens conversely are softer magnetic
materials with low remnant magnetization and coercive force. Improvements to both of
these experiments and further testing are proposed to verify these findings.
Timetable
Date
March 1, 2005
March 7, 2005
March 28, 2005
April 25, 2005
June 6, 2005
July 4, 2005
Goals
Literature research is completed
Thesis Proposal is completed
TEM thinning is completed
TEM testing and analysis completed
All microstructure analysis is completed
LabVIEW function generators and data acquisition virtual
instruments are completed
August 1, 2005
 Solenoids and apparatus for experiments are set up
 Gaussmeter is calibrated
August 29, 2005
Magnetostriction tests completed
September 26, 2005 Magnetic induction tests completed
October 31, 2005
 Reverse magnetostriction tests completed
 All laboratory experiments completed
December 5, 2005
Data Analysis completed, begin writing thesis paper
February 27, 2006
Thesis completed
March 13, 2006
PowerPoint slides completed
March 27, 2006
Thesis Presentation
References
1. D. J. Morrison, Y. Jia and J. C. Moosbrugger. Cyclic Plasticity of Polycrystalline
Nickel at Low Plastic Strain Amplitude: Constricted Hysteresis Loops. Department of
Mech. and Aero. Eng., Clarkson University, September 13, 2000.
2. J. C. Moosbrugger, D. J. Morrison, Y. Jia, D. Zhou. Single Crystal Nickel: Data for
Five Plastic Strain Amplitudes.
http://people.clarkson.edu/~moose/single_crystal_nickel.htm
3. Barrett, Craig R. Principles of Engineering Materials. Prentice-Hall, Inc. 1973.
4. Smith, William Fortune. Principles of Materials Science and Engineering, 2nd edition.
McGraw-Hill, 1990.
5. Smith, William Fortune. Foundations of Materials Science and Engineering, 3rd
edition. McGraw-Hill, 2004.
6. Vasina, R. Changes of Ferromagnetic Parameters during Cyclic Stressing. January 13,
1993.
7. D. E. Scherpereel, L. L. Kazmerski, and C. W. Allen. The Magnetoelastic Interaction
of Dislocations and Ferromagnetic Domain Walls in Iron and Nickel. Metallurgical
Transactions, Volume 1, February 1970 – 517.
8. H. Mughrabi, R. Kutterer, K. Lubitz, and H. Kronmuller. Magnetic Studies on
Cyclically Deformed  –Iron Single Crystals. September 20, 1976.
9. R. S. Carmichael. Magnetomechanical Behaviour of Nickel and Cobalt, Particularly
During Fatigue Deformation. Acta Metallurgica, Vol. 17, March 1969.
10. J. Kaleta and J. Zebracki. Application of the Villari Effect in a Fatigue Examination
of Nickel. Fatigue & Fracture of Engineering Materials & Structures, Vol. 19, No. 12,
1996.
11. H. D. Schumann. Changes of Coercive Force of Polycrystalline Nickel Specimens
within a Single Load Cycle after Cyclic Plastic Push-Pull Deformation. May 18, 1973.
12. Bozorth, Richard M. Ferromagnetism. IEEE Press, 1978.