Materials Engineering Lab: Hardening, Impact Testing, and Analysis

This materials engineering assignment details an experiment on hardening and impact testing using steel (BCC) and aluminum (FCC). The aim is to determine the effect of different hardening treatments and crystal structures on material properties, specifically toughness and hardness, by measuring Vickers hardness and impact energy. The experiment involves heat treating and quenching both materials, followed by Charpy impact tests and Vickers hardness tests. Results are presented in tables and charts, showing the relationship between temperature, absorbed energy, Vickers hardness, and diagonal length of indentations. The discussion analyzes the deformation behavior, fracture shapes, and the impact of temperature on energy absorption. The conclusion highlights the correlation between experimental and theoretical data, emphasizing the influence of heat treatment and temperature on material properties. The assignment also answers questions related to the effect of heat treatment and temperature on toughness, the importance of toughness in structural safety, and the relationship between hardness, strength, and toughness. The reference section includes relevant material science and engineering resources.

INSTITUTION:
STUDENT NAME:
COURSE:
UNIT: Materials Engineering
UNIT CODE: ENG 364
PROFESSOR’S NAME:
EXPERIMENT: Hardening and Impact Testing
DATE OF EXPERIMENT:

AIM
The main aim of this experiment is to use metals steel (BCC) and aluminum (FCC) to determine
effect of different hardening treatments and the crystal structure on material properties and
toughness by considering the Vickers hardness and the impact energy values.
INTRODUCTION
The carbon steel both high and medium is heat treated to form Austenite and then quenched in
either water or oil to form martensite. The formed martensite is very brittle and it is tempered so
as to increase its toughness.
Aluminum is treated through solution treatment so as to harden it at about 540C for an hour and
then quenched. The heat treated and quenched aluminum is then taken through age hardening at
175C for nearly 8 hours to further harden it.
The test hardness tests are the impact hardness test and the Vickers hardness test. The impact
testing for both the charpy and izod involve the use of a machine that as a pendulum moving at a
velocity of 3 to 4 m/s and the test piece sample to be used is a square of 10mm*10mm. The
machine has a notch angle of 45 degrees, 2mm deep and a root radius of 0.25mm. The energy
observe on the machine scale display during the impact denotes the toughness of the specimen
material.
The Vickers hardness testing involve the calculation of the Vickers hardness number HV given
by the equation;
H=1.854 P
d2
Where P=load ( Kg ) .
d=arithmetical mean of two diagonals of theidentation ( mm ) .
Diamond pyramid hardness test used is advantages over the Brinel hardness in since the hardness
number is independent of the size of the load used since all the impressions made by the

pyramid head diamond is have similar geometrically over an appropriate force range selected.
The machine digital readout display denotes the material hardness value.
METHODS AND MATERIALS
The Charpy impact and Vickers hardness methods testing techniques was used; the materials
used are the treated and different crystal structure of aluminum and carbon steel.
RESULTS
CHARPY TEST RESULTS
Temperature 0oC
Sample Break
Quenched 2J
Aluminum 38J
mild steel 180J
Temperature 27oC
Sample Break
Quenched 2J
Aluminum 66J
mild steel 124J
Temperature 80oC
Sample Break
Quenched 9J
Aluminum 64J
mild steel 144J
Note: The energy represent a value of energy absorbed in breaking the specimen
VICKERS HARDNESS TEST RESULTS
Quenched specimen
Hardness 475HV
Diagonal 19.750μm

Steel specimen
Hardness 79.8HV
Diagonal 48.214 μm
Aluminum specimen
Hardness 432HV
Diagonal 20.711μm
CHARTS
0 27 80
0
50
100
150
200
250
ENERGY ABSORBED VS TEMPERATURE
mildsteel
Aluminium
quenched sample
Temperatures (oC)
Energy absorbed (J)

Quenched 19.75 Aliminium 20.711 Steel 48.214
0
50
100
150
200
250
300
350
400
450
500
VICKERS HARDNNESS (HV) VS DIAGONAL (μM)
hardnness (HV)
Diagonal (μm)
Hardness (HV)
DISCUSSION
When the test samples are taken through the test by subjecting it to load at different points the
samples deforms. The shape of the deformation mainly depend on the material under the test and
the temperature at which the test is performed, the general fracture shapes formed in Charpy test
is a complete fracture while in Vickers test is pyramidal shape indentation and a fracture at the
point of stress concentration.
The graphical chart of Charpy test indicates a relationship between the amount of energy
absorbed and the temperature at which the material is under test, the variation in the amount of
energy of the different test samples at different test samples clearly denotes that the toughness of
different materials varies with temperatures and hence a variation in the amount of absorbed
energy to cause the sample to fracture or deform.
At higher temperatures the absorbed energy in Charpy test is higher over a wide range of
temperature for both steel and aluminum indicating that the both metals are undergoing ductile
deformation and at low temperature the absorbed energy for both is low indicating a brittle
deformation. The quenched sample at higher temperature absorption energy is low over wide
temperature indicating brittle deformation and ductile deformation over low temperatures.

The Vickers chart indicates the relationship between the Vickers hardness and the diagonal, the
amount of energy absorbed is inversely proportion to the length of diagonal. A small diagonal
has an overall small surface area exposed resulting in more energy being absorbed by the
material unlike in large diagonal.
CONCLUSION
The test performed indicate a relationship of the experimental data and the theoretical data, according to
Callister steel undergoes ductile deformation at higher temperatures and brittle deformation at low
temperature which was proved experimentally by Charpy test this allow engineers to applying alloying
techniques so that the material formed can be suitable at all temperatures . The toughness of the material
is show to depend on the temperature of the sample that tends to alter the material grain structure. The
Vickers hardness test further proofs that the energy (pressure) absorbed by the material is inversely
proportional to the area.
The test can be improved by proper calibration of the charpy test equipment to ensure accurate data
readings, ensuring the material used in the Vickers hardness test has the same diagonal for easy
comparison and proper recording of the experimental data.
Questions
1. Can the toughness be changed by heat treatment? Why?
 Yes
 Heat treatment and quenching or tempering affects the material microstructure by
changing its size and distribution which affects the toughness. Steel for example
when subjected to heat treatment its strength and toughness are affected, its
microstructure which is composed of cementite and ferrite matrix changes their size
and distribution which affects the toughness.
2. Can temperature of use affect the material toughness? Why?
 Yes
 The temperature affects the material toughness at higher temperatures the material
atoms are in random motion and are readily dislocated they thus undergoes plastic

deformation before fracturing while at lower temperature atoms of the material are
static thus very brittle and fracture under impact.
3. How is toughness important to improve safety in structures and components?
The toughness indicate the amount of energy the material of the structure will absorb before
fracturing, it shows the relationship between the material ductility and brittleness. It improves
the safety in that it clearly indicates the period that the component will remain in service
before a crack grows long enough to appoint that the cross-sectional area of the structure
cannot further support load imposed on it and the structure finally fracture.
4. Discuss the relationship and possible compromises between hardness, strength and toughness
in the applications of materials.
The material hardness indicates the ability of a material to resist the deformation, the strength
indicates how particular material will withstand an applied load without undergoing failure and
the toughness indicates amount of energy that the material will withstand in the process of
fracturing.
The microstructure and the distribution along and within the material influences the material
hardness, a closely packed microstructure closes all the the spaces such that when a load is
applied in it the closed packed material does not deform since they are closely packed until it is
very hard. The very closely packed grains builds or ensures that the material is hard and thus
develop the material strength which on application of load it will continue to withstand before the
grains disorient to develop a crack and the toughness indicates a combination of both the material
hardness and strength the material when hard and strong it will serve for a particular time frame
under a certain load. The toughness actually measure the time that the material will be under
excellent service before it start to crack and crack by measuring the energy of the load applied.
REFERENCE
1. Callister and Rethwisch Material science and engineering… an introduction.
2. Kohd b. Harun, Goh Kian Seong and Jasmin Baba -Effect of heat treatment on toughness and
strength properties of C-Mn steel.
3. Callister- Fundamentals of Materials Science and Engineering-An Interactive
4. Dr Brian N Leis (2013)- The Charpy impact test and its applications