International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
Wear Characterization of Ti-5Al-3V-2.5Fe Alloy Produced by
Recycling of Machining Chips
Abdel-Wahab El-Morsy
Mechanical Engineering Department, Faculty of Engineering-Rabigh, King Abdulaziz University,
P.O. Box 344, Rabigh 21911, Kingdom of Saudi Arabia
Also: Mechanical Engineering Department, Faculty of Engineering-Helwan, Helwan University,
1 Sherif Street, Helwan 11792, Cairo, Egypt
Abstract — This paper describes the application of
experimental design techniques to characterize the
wear behaviour of Ti-5Al-3V-2.5Fe alloy produced by
the recycling of machining chips. Application of
experimental design technique enabled us to confirm
the significance of the factors affecting the wear
behaviour with a minimum number of experiments.
The experiments of sliding wear were performed using
a pin-on-ring wear apparatus against a hardened
tool-steel counterface under loads range of 50 – 400
N, and within a sliding velocity range of 0.2 – 2.0 m/s.
Microstructural investigations on the worn surfaces
were undertaken using a scanning electron
microscope. In the mild wear region, the wear rates
increased linearly with the sliding velocity and the
applied load. The linear relationship indicates that
steady state has been achieved. In the severe wear
region, the wear has been found to increase almost
proportionally with applied load and sliding velocity.
Keywords — Dry sliding wear, Recycling, Machining
chips, Ti-alloy.
I. INTRODUCTION
When metal products are manufactured,
considerable amounts of waste in the form of chips
and discards are produced. This waste and scrap is
returned to melting, whereby some of the metal is
recovered and reutilized in production processes ([1] –
[6]). Amongst the different types of materials,
titanium and titanium alloys are commonly used in
industry [7], marine [8], and orthopedic prostheses
[9]-[10] where high strength and low density are of
primary importance. The waste of these materials
usually has the form of chips coming from the
machining of semi-finished products. In the process,
40% of scrap is generated [11]. If properly controlled,
addition of scarp is fully acceptable and can be used
even in materials for critical application [12]. With the
large amount of titanium used, there is also a large
amount of titanium and Ti-alloy scrap to recycle from
these various forms of its property use.
When considering Ti-alloys for application as
orthopaedic prostheses it is important to consider their
corrosion resistance and wear behaviour [13]. When
they are subjected to wear, however, the passive layer
can be removed allowing active corrosion to occur
while the alloy repassivates. Interest has grown in the
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tribological behaviour study of Titanium alloys in the
past decades ([14]-[18]). However, it was reported that
Ti-6Al-4V possessed a low sliding wear resistance
because of the low resistance to plastic shearing and
low protection exerted by surface oxides [19]. This
study explores the wear characteristics of recycled Ti5Al-3V-2.5Fe alloy machining chips. In this work, the
experimental design was used to clarify the effect of
the wear parameters, including applied load and
sliding speed on the sliding wear mechanisms of Tialloy.
II. EXPERIMENTS
The experiments were conducted using a titanium
alloy containing 5.5% Al, 3.35% V, and 2.5% Fe
prepared by remelting of machining chips in a 10 kg
vacuum-induction melting furnace. Ti-alloy chips are
contaminated mainly with the coolants and lubricants
used in machining (usually with oil emulsion) and also
contaminated by the inclusion of machine-tools (steel
chips and machine-tool tips made from carbide)
during the machining process. The emulsion was
removed from the chips by a chemical method and the
magnetic separation was used to eliminate the steel
chips. Machining chips from fabricators who use
carbide tools are acceptable for remelting, only, if all
carbide particles adhering to the chips are removed.
The liquid metal was cast in a permanent graphite
mould. The remelting process was carried out under a
flow of argon gas covering the charging materials
during heating and melting process to prevent any
reaction that could be occurred with oxygen or water
vapour. In the present work, a sufficient amount of hot
forging (corresponding to a reduction ratio in area of
80%) was carried out below the -transus i.e., between
1000-950 C after 30 min. homogenization [20]. The
hot forged bars were then air cooled.
Dry sliding wear tests were performed on a
Tribometer testing machine of pin-on-ring type wear
apparatus against stainless steel counterface [21] as
shown in Fig. 1. Wear test specimens in the form of
cylindrical pin with 12mm in length and 8mm in
diameter were machined from the forged specimens.
The wear experiments were performed in air at 25 C
with dry conditions. The stainless steel counterface
ring has 73 mm outer diameter and 63Rc surface
hardness. Before and after each test, the specimens
were rinsed in acetone and dried in air. The mass
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
losses were calculated from the differences in weight
of specimens measured before and after the sliding
tests (after removing any loose debris) using a
precision balance (0.001 gm.). The volumetric wear
rate was estimated in the unit of mm3/m. The tests
were carried out in a sliding velocity range of 0.2 and
2 m/s and a load range of 50 and 400 N. The eroded
surface was observed by scanning electron microscope.
velocity range (0.6 m/s) and it is apparent that the
wear rate is greater at the higher applied load.
The effect of the applied load on the volumetric
wear rate of the forged specimens at constant sliding
velocities 0.2, 0.6, 1.0, and 2.0 m/s is shown in Fig. 3.
The wear rate-applied load relationship under varying
sliding velocity exhibits that at 0.2 m/s, the wear rate
increases with the increasing in the applied load until
the highest applied load. At 0.6, 1.0 and 2.0 m/s
sliding velocity, the wear rate increases linearly with
increasing applied load up to 250 N. Thereafter,
further increases in applied load increase the wear rate
abruptly
0.40
400 N
Wear rate, mm3/m
0.35
0.30
0.25
0.20
150 N
0.15
0.10
100 N
0.05
50 N
0.00
0
0.5
1
1.5
2
2.5
Slidning Velocity, m/s
Fig. 1 Photo and schematic illustration of Tribometer testing
machine
III. RESULTS AND DISCUSSION
The volumetric wear rates for the forged specimens
are plotted against sliding velocity at constant applied
load of 50, 100, 150, and 400 N in Fig. 2. The
volumetric wear rate was estimated in the unit of
mm3/m by dividing the mass loss by the density of the
alloy. At all applied load, the wear rates increased
with increasing the sliding velocity. At low applied
load of 50 and 100 N, the wear rates increased linearly
with the sliding velocity and there was no drastic
increase in the slopes of the wear rate versus sliding
velocity curves until the highest sliding velocity (2
m/s). The linear relationship indicates that steady state
has been achieved. At applied load of 150 N, the wear
rate increased slightly as the sliding velocity increased
up to 0.8 m/s thereafter, with further increases in the
sliding velocity more than 0.6 m/s, the dependence of
wear rate on sliding velocity became more pronounced.
At high-applied load (400 N), large changes in the
slope of the wear rate occurred at a certain sliding
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Wear rtae, mm3/m
Fig. 2 Effect of sliding velocity on the wear rate at different applied
load.
0.40
2.0 m/s
0.35
0.30
0.25
0.20
1.0 m/s
0.15
0.6 m/s
0.2 m/s
0.10
0.05
0.00
0
100
200
300
400
Applied Load, N
Fig. 3 Effect of applied load on the wear rate at different sliding
velocity.
Fig. 4 shows the surface morphology of the forged
specimens after dry sliding wear at 50 N applied load
and different sliding velocity. Numerous grooves and
scratch marks, mostly parallel to the sliding direction,
are evident on all the worn pins. Such features are
characteristics of abrasion, in which hard particles in
between the contacting surfaces, plough or cut into the
pin, causing wear by the removal of small fragments.
(a) 0.2 m/s
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
fragments are worn only during the initial contact with
an abrasive particle. Fig. 5 shows the surface
morphology of the forged specimens after dry sliding
wear at 0.2 m/5 sliding velocity and different sliding
velocity
(a) 50 N
Sliding direction
Sliding direction
(b) 0.6 m/s
Sliding direction
(b) 150 N
Sliding direction
(c) 1.0 m/s
Sliding direction
(c) 400 N
Sliding direction
(d) 2.0 m/s
Sliding direction
Fig. 5 SEM micrograph of worn out surface after sliding at 0.2 m/s
velocity and applied load (a) 50 N, (b) 150 N, and (c) 400 N
Sliding direction
Fig. 4 SEM micrograph of worn out surface after sliding at 50 N
load and sliding velocity (a) 0.2 m/s, (b) 0.6 m/s, (c) 1.0 m/s, and (d)
2.0 m/s..
This suggests that abrasion took place primarily via
ploughing, in which material is displaced on either
side of the abrasion groove without being removed, or
through wedge forming, where tiny wedge-shaped
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Fig. 6 shows the severely of plastic deformation
layer at the worn surface tested at 400 N applied load
and 0.2 m/s sliding velocity (magnification X500).
These features are indicating the occurrence of severe
metallic wear. The transition to severe wear was
accompanied by a significant increase in the
roughness of worn surface of specimens. The severely
deformed metallic layers extruded along the sliding
direction and out of the contact surface of the
specimen. The figure shows plastic yielding caused by
decreasing of yield stress due to the heating.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 28 Number 5 - October 2015
[2]
[3]
[4]
[5]
Sliding direction
[6]
Fig. 6 SEM micrograph of worn out surface after sliding at 2.0 m/s
velocity and 50 N applied load (magnification X500)
[7]
[8]
IV. CONCLUSION
Pin-on-ring dry sliding wear tests of Ti-5Al-3V2.5Fe alloy against a stainless steel counterface were
carried out under loads range of 50 - 400 N, and
within a sliding velocity range of 0.2 - 2.0 m/s.
Volumetric wear rates were measured as a function of
applied load and sliding velocity.
At low applied load of 50 N, the wear rates
increased linearly with the sliding velocity until
the highest sliding velocity (2.0 m/s). The linear
relationship indicates that steady state has been
achieved. At 100 and 150 N applied load, wear
rate is not significant while at high-applied load
(400 N), the wear rate is deteriorative and a large
changes in the slope of the wear rate occurred at a
certain sliding velocity range (0.6 m/s).
At low sliding velocity of 0.2 m/s, the relationship
between weight losses versus applied load is a
linear relationship and load is not effective on the
wear rate. However, at 1.0 and 2.0 m/s sliding
velocity, applied load over 100 N leads to drastic
wear rate.
At severe wear conditions, the worn surface
exhibits plastic deformed layers. On the other
hand, at soft wear conditions, the worn surface
shows compacted layers with grooves aligned in
the sliding direction.
Scanning electron microscope of wear surfaces
revealed that the sliding wear behaviour of Ti5Al-3V-2.5Fe alloy can be classified into two
main wear regimes, mild wear regime and a
severe wear regime. Sliding at applied load 50 N
reveals crater and as main mechanisms
responsible for material loss indicating the
occurrence of mild wear. In severe wear region
gross plastic deformation and plastic yielding can
be noticed on the wear surface after dry sliding.
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