International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
Investigation of Wear Analysis of AZ91D
Magnesium Alloy Reinforced With TiC & BN
Nithin N S1#, Hari Venkit2#
1
M.Tech Student, 2Assistant Professor
#
Department of mechanical Engineering, Mar Baselios College of Engineering TVM, Kerala, India
Abstract — Magnesium is the lightest structural
metal. Magnesium alloys are mixtures of magnesium
with other metals, often Al, Zn, Mn, Si, Cu, rare earths
and zirconium. The Mg alloys has excellent stiffness
and strength-to-weight ratio with good environmental
corrosion resistance, high conductivity, electrical and
thermal properties. Mg alloys are cost effective with
good finishing and recyclability. AZ91D is the most
widely specified magnesium die casting alloy. This
high-purity alloy has an excellent combination of
mechanical properties, corrosion resistance, and
castability. This work investigates about the
improvements in the properties of the AZ91D Mg
alloy, reinforcing with titanium carbide (TiC) and
boron nitride (BN). The work includes; fabrication of
the AZ91D/TiC composite, fabrication of hybrid
composite reinforced with optimum composition of
TiC and BN. The wear properties are analysed
through the wear analysis and micro level inspection
using optical microscope. The hybrid composite and
the composite, AZ91D/ (5%) TiC shows better wear
resistance properties. But, the wear resistance of the
composite AZ91D/TiC and the hybrid composite
AZ91D/TiC/BN is not enough to support the severe
loading conditions and the consequent particulate TiC
depletion is also observed. Further researches are
needed to reduce the particulate concentration.
Keywords — AZ91D, TiC,
microscope, Pin on disc wear test.
XRD,
Optical
I. INTRODUCTION
A composite is the combination of two
materials in which one of the materials is called as the
reinforcing phase, and is embedded in the other
material called as the matrix phase. The reinforcing
material can be in the form of fibers, laminates, or
particles and the matrix material can be metal, ceramic,
or polymer. Composites typically have a fiber or
particle phase that is stiffer and stronger than the
continuous matrix phase and serve as the principal
load carrying members. The composites are selected
for various applications, because of their better
properties compared to the base materials. The
following are various properties of composites: High
strength to weight ratio, High creep resistance, High
tensile strength at elevated temperatures, High
toughness, and Long life.
Based on the matrix material used,
composites can be classified as:
Metal matrix composites (MMC)
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Ceramic matrix composite (CMC)
Polymer matrix composites (PMC)
Based on the reinforcing material structure,
composites can be classified as:
Particulate composites
Fibrous composites
Laminate composite
The metal matrix composite is composed of
at least two constituent parts, in which the matrix will
be a metal and the reinforcing material can be a
different metal or another material such as ceramic or
organic compound. If there is at least three materials
are present, then it is called as a hybrid composite. In
structural applications, the matrix is usually a lighter
metal such as aluminium, magnesium, or titanium.
The reinforcement can be either continuous or
discontinuous. Continuous reinforcement includes
fibers such as carbon fiber or silicon carbide.
Discontinuous reinforcements are whiskers, short
fibers or particles. The reinforcement is used to
change the physical properties such as wear resistance,
friction coefficient, or thermal conductivity.
The methods used for solid state manufacturing of
metal matrix composites are
Powder blending and consolidation (powder
metallurgy)
Foil diffusion bonding
A. Friction and wear
Friction and wear can be described as the
responses of the system of bodies which are in
contact. Coefficient of friction and wear are the
parameters which are used to describe the state of
contact between two bodies in contact. Wear is related
to interactions between surfaces and specifically the
removal and deformation of material on a surface as a
result of mechanical action of the opposite surface.
Under normal mechanical and practical procedures,
the wear-rate normally changes through three different
stages:
Primary stage or early run-in period, where
surfaces adapt to each other and the wear-rate
might vary between high and low.
Secondary stage or mid-age process, where a
steady rate of ageing is in motion. Most of
the components operational life is comprised
in this stage.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
Tertiary stage or old-age period, where the
components are subjected to rapid failure due
to a high rate of ageing.
II. METHODOLOGY
The wear analysis of the composites are done
by the experimental method. The experimental work
includes; preparation of the die, fabrication of the
Az91D/TiC test specimens through the die casting
method. The wear analysis was carried using the pinon-disc experiment.
Powder metallurgical process is used to
prepare the specimens. Powder metallurgy is the
process of blending fine powdered materials, pressing
them into a desired shape or form (compacting), and
then heating the compressed material in a controlled
atmosphere to bond the material (sintering). The
powder metallurgy process generally consists of four
basic steps: powder manufacture, powder blending,
compacting, and sintering. Compacting is generally
performed at room temperature, and the elevatedtemperature process of sintering is usually conducted
at atmospheric pressure. Optional secondary
processing often follows to obtain special properties or
enhanced precision. The use of powder metal
technology bypasses the need to manufacture the
resulting products by metal removal processes,
thereby reducing costs. Initially powder metallurgical
products were used to replace casting for metals which
were difficult to melt because of their high melting
points. The properties of the product depending upon
the characteristics of metal powders. The main
physical and process characteristics are shape,
fineness,
size
distribution,
flow
ability,
compressibility, apparent density, purity, green
strength and sintering ability. The figure shows the
basic steps in the powder metallurgical process.
Fig.1 Pin-on-disc tribometer
Several industries face the problem of wear
on parts in service. Virtually any part that is moving in
service will be subject to wear at the contact point
with other parts. The consequence of this wear is that
parts need to be replaced, which costs money and
causes downtime on the equipment. The on-going
challenge of engineers in these fields is to find, or
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design, materials that are the most wear resistant, in
order to extend the life of the parts and will reduce the
frequency of part replacement. To study wear of the
materials, we must simulate the process of wear in a
controlled manner and study the effect on different
samples with the same test conditions. One way to
perform the wear is with a pin-on-disk test. In this test,
the sample to study is prepared as a pin or ball which
comes in contact with the surface of a rotating disc,
with a known force, to create the wear.
A. X-Ray Diffractometry
Fig.2 X-ray diffraction pattern
The chemical analysis of AZ91D/TiC is done
through the X-ray diffractometry. By comparing with
standard patterns (patterns of the basic alloy, AZ91D
reinforced with other particles and Al alloy reinforced
with TiC), the peaks of the composite represents the
following compound; Al12Mg17. These compound has
negligible effect on the composite wear test.
III. EXPERIMENTAL WORK
The wear analysis of the AZ91D/TiC
composite and the hybrid composite (AZ91D/TiC/BN)
were carried out through a series of experiments using
the pin on disc apparatus. The dry wear test is used for
the wear analysis. The specimens were prepared
through the powder metallurgy method. The metal
powders are mixed in the correct proportions and is
mixed thoroughly in the lathe about two hours at low
speed. The die for the compacting process is prepared
using the Oil Hardened Nickel Steel (OHNS). The die
is hardened to obtain better hardness to withstand high
pressure during the compaction. The die casting is
done using the compression machine. The die cavity is
filled with the powdered material, and is compacted to
the desired shape and size by applying a load of
200kN. The compacted specimen is then heat treated
to about 430°C at two and half hours. The heat
treatment of the specimen is done, to obtain good
blending between the particles in the specimen.
A. Test specimen
Three different compositions of the
AZ91D/TiC composite were prepared as the test
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
specimen. The compositions are AZ91D magnesium
alloy reinforced with 5%, 10%, and 15% of titanium
carbide. The results after the wear analysis of these
specimens shows that AZ91D/TiC reinforced with 5%
TiC has the least wear rate compared to the other
compositions. So, after the wear analysis of
AZ91D/TiC composite, the hybrid composite was
fabricated by reinforcing the AZ91D magnesium alloy
with the optimum compositions of the TiC and BN.
The optimum composition results of the Boron Nitride
was selected from the previous work, in which the
wear analysis of the AZ91D/BN composite was done.
All of the specimens are heat treated to get a better
bonding in between the particles in the specimen. The
specimens are 10mm in diameter and 20mm height,
which is suited to the pin on disc apparatus.
B. Experimental setup
Experiments have been conducted in the Pinon-disc type Friction and Wear monitor with data
acquisition system, which was used to evaluate the
wear behavior of the composite, against hardened
ground steel disc (High Carbon High Chromium Steel)
having hardness 65 HRC. The disc is 150mm diameter
and 8mm thick and is rotated by means of a motor.
The pin is fixed at the tool holder and it is connected
with the lever mechanism. The wear track diameter is
adjusted by adjusting the position of the lever
mechanism. The load is applied to the pin by means of
the string and pulley using the dead weights. The
apparatus is connected with the wear monitor with
data acquisition system. The wear rate, coefficient of
friction and the frictional force of the specimen is to
be calculated by means of sensor attached in the
machine and the result can be monitored and graphs
would be plotted in the computed connected to the
machine. In the wear monitor the speed of the disc can
be adjusted and also timer is available for setting up
the test duration.
This test method may be applied to a variety
of materials. The only requirement is that specimens
having the specified dimensions can be prepared and
that they will withstand the stresses imposed during
the test without failure or excessive flexure. The
materials being tested shall be described by
dimensions, surface finish, material type, form,
composition, microstructure, processing treatments,
and indentation hardness. For the pin-on-disk wear
test, two specimens are required. One, a pin (test
specimen) with a polished smooth surface, is
positioned perpendicular to the other, usually a flat
circular disk. A cylindrical piece, rigidly held, is often
used as the pin specimen. The test machine causes
either the disk specimen or the pin specimen to
revolve about the disk center. In either case, the
sliding path is a circle on the disk surface. The plane
of the disk may be oriented either horizontally or
vertically.
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C. Parameters for experiment
The parameters selected for the experiment
are; load, sliding speed and sliding distance. The
specimens are tested for two levels of these
parameters.
The test was carried out by considering these
different parameters because, the wear analysis can be
done accurately by considering different loading
conditions. The wear rate, frictional force, and
coefficient of friction can be different in each
conditions and the wear behavior can be explain with
better clarity. Usually the wear results are reported as
volume loss in cubic millimeters for the pin and disc
separately. The amount of wear is determined by
measuring appropriate linear dimensions of both
specimens before and after the test, or by weighing
both specimens before and after the test.
The test would be carried out with two levels
of the three parameters. So, there would be eight
experiments for the each composition. There are three
different compositions of AZ91D/TiC composite and
a hybrid composite. Thus there would be 32
experiments considering all levels of the parameters
and all of the compositions. Conducting 32
experiments will be time consuming. So, the number
of experiments was reduced without altering the test
parameters. For that, an optimizing technique was
used through the design of experiments. In the design
of experiments, different optimizing techniques are
used to reduce the number of experiments with least
error through the proper relation in between the
parameters.
The actual number of experiments are eight
which is optimized in the design expert as four. The
three parameters with two levels are optimized using
the Taguchi method. Here parameters are selected
randomly by keeping a relation between each other.
The experimental data corresponding to the optimized
parameters are shown in the table. The disc speed and
duration of the experiment is calculated with respect
to the different parameters chosen for sliding distance
and sliding speed. Thus the total number of
experiments is reduced to 16.
Table. I Optimized experimental data
Parameters
Ex
No
Disc
Speed, N
(rpm)
Test
duration
(s)
0.5
96
210
200
1
191
200
30
100
1
191
100
30
200
0.5
96
400
Load
(N)
Sliding
Distance
(m)
Sliding
speed
(m/s)
1
10
100
2
10
3
4
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
IV. RESULTS AND DISCUSSIONS
In general, the wear rate of the materials are
affected by means of several factors such as
operational parameters, topography of the surface
contact, geometry, speed, load, and coefficient of
sliding friction. In addition, material and
environmental parameters, various material hardness,
temperature, elasticity, breakage, as well as thermal
properties, also affect wear. The type and amount of
lubrication and surface cleanliness also affect wear.
Using the pin on disc test method, we cannot test the
materials for the actual service conditions. In actual
conditions more factors are affected with the contact
surfaces thus making the conditions more complicated.
That is, for simulating the actual conditions
considering all factors the non-linear analysis should
be done, which is not possible using the pin on disc
test method.
The results of the wear rates of the materials
are generally described using the plots of wear volume
versus sliding distance, sliding time, applied load etc.
Such plots may display non-linear relationships
between wear volume and distance over certain
portions of the total sliding distance, and linear
relationships over other portions. The non-linearity
can be due to the improper contact between the pin
and the disc or may be due to material properties. The
delamination at the contact surface causes slippage
which gives inaccurate wear results.
Fig.4 Wear rate vs sliding time for AZ91D/TiC/BN
and AZ91D/BN composites for S2
A. Hybrid composite: AZ91D/TiC/BN
Figures 3 to 6 shows the variation of wear
rate corresponding to sliding time under different
optimized parameters. The hybrid composite was
fabricated by reinforcing the AZ91D magnesium alloy
with the optimum compositions of TiC and BN. The
AZ91D shows least wear rate, when it is reinforced
with 5% of TiC and BN which is the optimum value.
Fig.3 Wear rate vs sliding time for AZ91D/TiC/BN
and AZ91D/BN composites for S1
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Fig.5 Wear rate vs sliding time for AZ91D/TiC/BN
and AZ91D/BN composites for S3
Fig.6 Wear rate vs sliding time for AZ91D/TiC/BN
and AZ91D/BN composites for S4
Comparing the plots of the composites, it is
clear that the wear rate of the composites depends
upon the different composition of the material added
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
and the sintering temperature of the samples. For the
analysis, four different samples with different
parameters are selected. They are named as; S1, S2,
S3 and S4. The applied load for the samples S1 and S2
is 10N and for the samples S3 and S4 the load is 30N.
Two levels of sliding speed is selected; 0.5m/s is
given to the samples S1 and S4, and for S2 and S3 the
sliding speed is 1m/s. The two different sliding
distances 100m and 200m are provided to S1, S3 and
S2, S4.
Among the all four samples of the hybrid
composite AZ91D/TiC/BN, the sample 1 shows better
wear property. The sample 1 of hybrid composite also
has less wear rate than the S1 of AZ91D/TiC (10%)
composite and has greater wear rate than the
AZ91D/TiC (5%). But for all other samples, S2, S3
and S4 of hybrid composite has prominent wear rates.
The sample S3 has the greatest wear rate. This can be
due to the high loading and sliding conditions. The
samples S2 and S4 has almost similar wear rates, even
though the loading conditions are different. But the
wear rate is slightly greater for S4 due to the greater
load (30N). The wear property for the hybrid alloy can
be improved by reducing the percentage of Titanium
Carbide and Boron Nitride, since the 5% TiC and BN
shows the wear rates satisfactorily.
For the lowest loading conditions (sample 1),
the hybrid alloy has better wear properties. As the
percentage of TiC and BN reduces the wear rates are
also reducing. Thus further analysis can be done by
reducing the reinforcement percentage with low
loading and sliding conditions. For keeping the
continuous contact in between the pin and disc, the
surface of the pin should be properly machined and
polished. The primary checkup of the apparatus
should be carried out regarding the cleanliness and
wobbling of the disc. The atmospheric conditions can
also affect the test parameters there by recording the
inaccurate wear results.
Fig.7 Optical image of AZ91D/TiC/BN alloy for
test samples a) S1; b) S2; c) S3; d) S4.
Figure 7 shows the optical images of the
worn surfaces of the hybrid composite. It can be seen
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that, grooves are created in the complete surface area
due to the depleted abrasive particles from the contact
area. An amount of particles were detached out from
the surface which then results in ploughing and the
creation of grooves. The extent of detachment of the
particles are determined by the applied load, sliding
speed, surface contaminations and the sliding distance.
B. AZ91D/TiC composite
The basic magnesium alloy AZ91D is
reinforced with 5%, 10%, and 15% of titanium carbide
to prepare different compositions of AZ91D/TiC
composite. The composites shows better wear
property than that of the basic magnesium alloy
AZ91D. Comparing the wear properties of the all
samples of the three compositions, the composite
AZ91D reinforced with 5% of TiC has the least wear
rate. When the percentage of Titanium Carbide
increases the wear rate also increases. So, the
composite AZ91D reinforced with 15% of TiC has the
highest wear rate compared with the three specimens.
But, when the wear results of the samples (S2, S3 and
S4) of the hybrid composite are also considered with
these three compositions, the hybrid composite gives
the prominent wear rate. But still the sample S1 of the
hybrid composite gives better wear properties than the
compositions 10% and 15%. The minimum wear rate
among the three compositions is 33.74µm and
maximum wear rate is 138.97µm.
Corresponding to the increased applied load,
the wear rate of the composites also increases because
of heat generated during the friction in between the
contact surfaces. The reason for the lower wear rate in
the composite AZ91D/TiC (5%) as well as for the
hybrid composite is the presence of the reinforcing
materials; TiC and BN. TiC, is an extremely hard
ceramic material commercially used in tool bits. It
gives better resistance to wear, corrosion, and
oxidation. Because of excellent thermal and chemical
stability, boron nitride ceramics are traditionally used
as parts of high-temperature equipment.
Fig.8 Optical image of AZ91D/TiC (5%) composite
for test samples a) S1; b) S2; c) S3; d) S4
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
Figure 8 represents the optical image of the
worn out surface of the AZ91D/TiC composite
reinforced with 5% of TiC. The grooves and detached
particles can be seen in the worn surface due to the
different loading and sliding conditions. Wear rate of
the AZ91D/TiC (5%) composite is less compared with
the other compositions. This because of the better
reinforcement and bonding of the TiC with the basic
alloy. The intermolecular bonding in between the
particles provides the high wear resistant property to
the composite. The samples S1 and S2 has the lowest
wear rate and high wear results are observed at the
samples S3 and S4.
Figure 10 represents the optical image of the
AZ91D/TiC (15%) composite which is reinforced
with 15% of TiC. The figure shows more wear tracks
and grooves than the other compositions, because of
the highest percentage of TiC. Observations shows
that the intermolecular bonding in between the basic
alloy particles and the TiC particles is weaker than
other compositions which leads to increased material
removal rate. We can clearly see the detached TiC
particles in black color. Deep cuts are also observed
on the worn out surface which is due to these detached
particles. Here samples 3 and 4 has the highest wear
rate.
V. CONCLUSIONS
Fig.9 Optical image of AZ91D/TiC (10%)
composite for test samples a) S1; b) S2; c) S3; d) S4.
Figure 9 represents the optical images of the
worn out surface of theAZ91D/TiC composite
reinforced with 10% of TiC. Here the percentage of
the TiC is greater than AZ91D/TiC (5%) and so the
wear rate is also higher. The black dots in the figure
represents the TiC particles .Because of the
detachment of the TiC particles, the wear rate
increases due to the abrasion in between the
contacting surfaces. The sample 1 has greater wear
rate than the hybrid composite. But, the highest wear
rate is observed in the sample 3 and lowest wear
occurs on the sample 2.
The following conclusions can be drawn
from the present investigation:
1. Under dry sliding conditions, with increase in
load, the wear rate of the AZ91D/TiC
composite and the hybrid composite
AZ91D/TiC/BN increases linearly with
sliding distance.
2. The results through the investigation of wear
analysis shows that, among the three
compositions (5%, 10% and) of the
AZ91D/TiC composite, the composite
reinforced with 5% of TiC particles has the
positive wear resistance behavior.
3. The wear analysis of the hybrid composite of
AZ91D/TiC reinforced with 5% of Titanium
Carbide and 5% of Boron Nitride indicates
lower wear rate for the lowest loading and
sliding conditions only. But, for all other
conditions the hybrid alloy has the highest
wear rate than the other composites.
4. The hardness, wear resistance and surface
smoothness can be improved by reinforcing
the base alloy AZ91D with TiC and BN.
5. The wear resistance of the composite
AZ91D/TiC and the hybrid composite
AZ91D/TiC/BN is not enough to support the
severe loading conditions and the consequent
particulate TiC depletion is also observed.
Further researches are needed to reduce the
particulate concentration.
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