N. NDOU, E. AKINLABI: MICROSTRUCTURE, WEAR RESISTANCE AND MICROHARDNESS OF W-PARTICLE- ...
269–274
MICROSTRUCTURE, WEAR RESISTANCE AND
MICROHARDNESS OF W-PARTICLE-STRENGTHENED Ti6Al4V
COMPOSITE PRODUCED WITH LASER METAL DEPOSITION
MIKROSTRUKTURA, ODPORNOST PROTI OBRABI IN
MIKROTRDOTA LASERSKO IZDELANEGA, Z W-DELCI
OJA^ANEGA Ti6Al4V KOMPOZITA
Ndivhuwo Ndou,
1,2
Esther Akinlabi
2
1
University of South Africa, Department of Mechanical and Industrial Engineering, Florida Johannesburg 1710, South Africa
2
University of Johannesburg, Department of Mechanical Engineering Science, Kingsway Campus, Johannesburg 2006, South Africa
nndou@unisa.ac.za
Prejem rokopisa – received: 2017-06-19; sprejem za objavo – accepted for publication: 2017-11-03
doi:10.17222/mit.2017.076
The objective of this work was to investigate a Ti6Al4V/W composite coated by means of the laser-power process. The
microhardness profile, microstructure and wear properties of W particles, produced with laser metal deposition (LMD), were
explored. Different power-flow rates were used in the study, ranging from 800 kW to 1400 kW, with the other parameters kept
constant. The results showed that the LMD process allows the production of a suitable bond between the substrate zone and the
clad zone. It was found that LMD has a direct effect on the microhardness and microstructures. The microhardness and wear
resistance of the deposited material produced with LMD were higher than those of the Ti6Al4V substrate. The wear result
obtained at a laser power of 1000 W revealed better wear resistance than that of the composite coating obtained at 900 W or
1200 W.
Keywords: microhardness, microstructure, surface modification, wear resistance, wear volume
Predmet tega prispevka je opis raziskave kompozita Ti6Al4V/W, pri katerem je bil W vne{en v substrat z laserskim postopkom.
Avtorji raziskave so dolo~ili profil mikrotrdote, mikrostrukturo in odpornost proti obrabi plasti W delcev, ki so bili vne{eni s
postopkom laserske depozicije kovine (LMD, angl.: Laser Metal Deposition). V {tudiji so uporabili razli~no mo~ laserja v
obmo~ju med 800 kW in 1400 kW, pri ~emer so ostale parametre obdr`ali konstantne. Rezultati ka`ejo, da je z LMD procesom
mo`no izdelati primerno vez med Ti6Al4V substratom (podlago) in nane{enim materialom (W). Avtorji so ugotovili, da LMD
proces vpliva direktno na mikrotrdoto in mikrostrukturo. Mikrotrdota in odpornost proti obrabi plasti, nastali z LMD
nane{enega materiala, sta vi{ji, kot jo ima osnovni Ti6Al4V substrat. Odpornost proti obrabi kompozitne plasti, izdelane z
mo~jo laserja 1000 W, je bolj{a kot so jo avtorji raziskave dosegli z mo~mi laserja 900 W in 1200 W.
Klju~ne besede: mikrotrdota, mikrostruktura, povr{inska modifikacija, odpornost proti obrabi, obseg obrabe
1 INTRODUCTION
In view of its thinness, the prevalent quality at high
temperatures, and good corrosion resistance, Ti6Al4V is
indispensable in the development of most parts utilised
in aerospace.
1,2
Because of the good chemical activity
and low thermal conductivity, titanium alloys are viewed
as hard materials.
3,4
A chemical reaction of titanium at a
high temperature brings about the creation of a strong
layer, prompting reduced tool life.
5
Parts for the aviation
industry are considered to be hard to machine owing to
their mechanical properties.
Tungsten powder is a vital material due to its wear
resistance, high hardness and excellent quality. However,
due to its composition, W cannot be machined effectiv-
ely by means of traditional procedures.
6
Instead, it can be
machined using non-conventional methods such as laser
metal deposition (LMD). Laser surface modification is
utilised to improve the surface of a workpiece because it
increases the life of the workpiece while reducing the
manufacturing cost,
7
and it guarantees the surface hard-
ness.
8
Many surface modifications have been utilised to
enhance the wear properties of titanium compounds,
with or without success; these include laser and plasma
surface treatment,
9
sol-gel processing
10,11
and nitriding.
12
Surface modification using lasers seems, by all accounts,
to be of interest in the light of the fact that lasers allow
high coherence and accuracy in a specific range without
damaging any part of the surface.
13
LMD processes such
as laser melting and laser cladding can produce coatings
with better metallurgical bonding.
Titanium alloys are essential for the developments
within the aeroplane industry and vehicle engines.
14
Close net-framed titanium fragments can, without a
doubt, be created at a significantly lower cost.
15–17
Previously, various technologies for making metal-
matrix composites (MMC) of various Ti mixes were
utilised.
18–22
LMD is viewed as a reasonable technology
for this purpose.
23,24
The LMD process entails the use of
the laser power that melts the top layer of a metal sub-
strate. Complex parts are produced by means of LMD at
Materiali in tehnologije / Materials and technology 52 (2018) 3, 269–274 269
UDK 67.017:620.193.95:669.295:669.71 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 52(3)269(2018)

a significantly lower cost than by means of conventional
methods.
25
Lately, it has been demonstrated that tungsten parti-
cles can be used in a titanium matrix, creating a Ti–W
coating of exceptional quality and good strength.
26
In the current study, investigations were conducted to
determine the effect of the laser power on the wear resis-
tance, microhardness and microstructure of the produced
Ti6Al4V/W composites using the LMD process.
2 EXPERIMENTAL METHODS
2.1 Equipment and sample preparation
Prior to the deposition procedure, the substrate was
cleaned using a sandblast machine with the specific goal
to remove the undesirable material to provide for suffi-
cient metallographic joining. The surface of the material
was cleaned with acetone to enhance the laser-control
retention. The deposition of Ti6Al4V/W particles was
performed at the National Laser Centre of the Council
for Scientific and Industrial Research (CSIR) in Pretoria,
South Africa, using a machine with a maximum power
of 4400 W. LMD was carried out using the laser tech-
nology employing a Kuka robot. The powder feeder was
loaded with Ti6Al4V and W powders at a flow rate
specifically relative to the rotational speed. It is better to
utilise isolated dual hoppers than pre-mixed powders, as
pre-blended powders are not of a uniform density.
25
Chambers were loaded with argon gas, which is utilised
to prevent oxygen contamination on a deposited sample
composite. Argon gas was used to prevent the deposited
samples from oxidising during the procedure, to control
the gas, to make the powder and to make the dissolved
metal flow in the anticipated direction.
The powder particles were injected into the dissolv-
ing pool through a coaxial nozzles, while a powerful
laser beam dissolved the deposited material over the sub-
strate or base metal (Figure 1).
2.2 Experimental procedure
A 10-mm Ti6Al4V sample plate with dimensions of
(200 × 100 × 10) mm was utilised as the substrate.
Dual-feeder hoppers were utilised to permit concurrent
cladding of the powders. The laser-beam diameter was
set at 2 mm and the beam space was kept constant at
2 mm throughout the process. After the deposition pro-
cedure, all the coated samples were cleaned to remove
the unwanted material. Figure 2 illustrates two separate
hoppers, each containing a different powder. The powder
feeder was set according to the predetermined ratio.
Table 1 depicts the process parameters used in this study.
Coated samples were produced utilising laser metal
deposition and the produced samples were designated
A1 to A5. The samples were mounted, with polyfast
resin, utilising a hot mounting press.
Table 1: Process parameters
Speci-
men
Power
(kW)
Scanning
speed
(m/min)
Powder-flow rate
(min
–1
)
Gas-flow rate
Ti6Al4V W Ti6Al4V W
A1 0.8 0.7 9.5 0.5 1.5 3
A2 0.9 0.7 9.6 0.6 1.5 3
A3 1 0.7 9.7 0.7 1.5 3
A4 1.1 0.7 9.8 0.8 1.5 3
A5 1.2 0.7 9.9 0.9 1.5 3
2.3 Microstructure
The coated samples were sectioned and mounted,
with polyfast resin, using a Lecco PR25 mounting-press
machine. After the mounting, all the samples were
grinded to reveal the coated surface. They were then
polished with 320 bonded papers using MD CHEM with
an OP-S suspension. After the polishing process, they
were cleaned with running water and acetone. The sub-
script was prepared with 100 mL H
2
O,3mLHF ,4mL
HNO
3
and (30 % H
2
O
2
,70%H
2
O). The polished spe-
cimens were first etched for 11 s to 16 s according to the
metallographic procedure. A microstructural analysis
was conducted using optical microscopy. Additionally,
investigations for characterising the samples were done
N. NDOU, E. AKINLABI: MICROSTRUCTURE, WEAR RESISTANCE AND MICROHARDNESS OF W-PARTICLE- ...
270 Materiali in tehnologije / Materials and technology 52 (2018) 3, 269–274
Figure 2: Double feeder of W and Ti6Al4V powders
Figure 1: Experiment set-up

by means of high-resolution images of SEM, and EDS
was used for the chemical analysis. The samples used for
analysing the microstructure were prepared metallurgi-
cally according to the E3-11 ASTM standard.
27
2.4 Hardness
The microhardness profile was determined using the
Vickers microhardness test. The hardness distribution
was measured according to the E384-11El ASTM stan-
dard.
28
The indentation load used was 500 g, with a
dwell time of 12 s, and the space among the indentations
was kept constant at 10 μm.
2.5 Wear-resistance testing
Dry-sliding-wear testing of the Ti6Al4V/W coating
was carried out by means of a CERT tribometer. The
samples, with dimensions of (200 × 100 × 100) mm,
were pressed under a load of 25 N. The wear resistance
of the Ti6Al4V/W coating was evaluated for a sliding
distance of up to 2000 m and a reciprocation frequency
of 20 Hz. Wear-scar images were obtained using high-
resolution images of SEM. The wear volume was
obtained by calculating the track area of the deposited
coating. Following the G133-05(2010) ASTM stan-
dard,
29
all the samples were tested on a dry-sliding-wear
tester.
3 RESULTS
3.1 Microstructure
The study was carried out on deposited Ti6Al4V and
W. Figures 3a to 3c show etched cross-sections on
scanning-electron-microscopy (SEM) micrographs of the
Ti6Al4V/W coatings deposited by means of laser metal
deposition at laser powers of (900, 1000 and 1200) W.
At the laser power of 1200 W, the microstructure
showed a degree of porosity. It can be attributed to the
extended solubility of air in the melt pool with the in-
creased heat input.
25
W-powder particles were uniformly
distributed at the laser powers of 900 W and 1000 W. W
particles at the laser power of 1200 W were evenly
distributed, with little porosity.
Figure 4 shows SEM micrographs of Ti64l4V/W
coated with a laser power of 1000 W. Figure 4a illus-
trates three zones, namely, the top surface of the coating,
the layer between the clad zone and the substrate, and
the heat-affected zone. Good bonding between the clad
zone and the substrate is also illustrated in Figure 4a.
Figure 4b shows Ti6Al4V needles forming a basket-
weave pattern. Figure 4c shows the heat-affected zone
and the microstructure of the deposited coating. At the
joining boundary line, the coating is characterised by a
N. NDOU, E. AKINLABI: MICROSTRUCTURE, WEAR RESISTANCE AND MICROHARDNESS OF W-PARTICLE- ...
Materiali in tehnologije / Materials and technology 52 (2018) 3, 269–274 271
Figure 4: SEM images of etched microstructures: a) direct laser
melting at 1 000 W, b) cross-section of top layers, c) cross-section of
deposited and heat-affected zones and d) cross-section of the
heat-affected zone and Ti6Al4V substrate
Figure 3: Etched SEM micrographs showing the coatings deposited at
various laser powers: a) 900 W, b) 1000 W and c) 1200 W

thin strip that is completely covered with W particles.
Figure 4d shows the microstructure of the heat-affected
zone and the substrate bonding. The Ti6Al4V/W coat-
ings produced at the laser power of 1000 W were
achieved with little dilution. The bonding between the
clad layer and the substrate is shown in Figure 4d,i n
which it is possible to identify where the coating and
substrate merge. It can be concluded that the coating on
the clad layer was strong, with less dilution. The W
coatings on the top surface of the coating reinforce the
material.
3.2 Microhardness
The coatings were indented from their upper surface
through to the substrate in accordance with ASTME
E1184. The increment in the microhardness was ob-
served on five samples with deposited coatings. Figure 5
shows the hardness profiles for various laser powers. The
hardness of the composite coating increased with the
increasing laser power. Be that as it may, the microhard-
ness measurement of the coating deposited at 1100 W
(N4) showed the lowest hardness. Figure 5 shows the
microhardness profiles of the coatings deposited at the
laser powers of 800–1200 W.
Figure 6 shows the laser power of 1000 W with the
highest hardness value of 719 HV. The hardness of the
substrate used was 350 HV. The hardness value for the
deposition zone (top layer) was 719 HV. The microhard-
ness measurement was conducted on all the samples, on
the cross-sections of the composites. Figure 6 shows the
highest hardness value of 719 HV. The highest value can
be contributed to the high level of martensite and the
generation of the Widmanstatten pattern.
These results show that the coating of W particles
improves the hardness of the material. They also show
that the coating at the interface between the HAZ and the
substrate was hard. The hardness increased in compari-
son to that of the substrate. This value is acceptable,
showing good bonding between the coating and the sub-
strate. No splits or cracks formed during the indentation
procedure, which means that the coating is solid.
3.3 Wear-resistance testing
Wear tests were performed on all the samples. Fig-
ure 7a shows the SEM microstructure of the wear track
formed by a sliding motion on Ti6Al4V/W. Figure 7b is
a higher-resolution micrograph of the wear track. The
wear-worn surface displayed numerous grooves and
debris arising from the detached material. The wear
observed on the Ti6Al4V/W composite coating entailed
abrasion and a blend of adhesion and plastic deforma-
tion. The abrasion takes place early on, as the tungsten-
carbide ball interacts with the surface of the substrate,
leading to the rubbing action of the two surfaces. Adhe-
sion occurs when the rubbing of the two surfaces
proceeds with no oil lubrication, causing strong adhe-
sion.
30
Strong adhesion creates high temperature and
results in the development of debris, which increases the
wear action. As the temperature continues to increase,
the wear debris solidifies and the sliding activity conti-
nues.
The effect of the load was observed during the sliding
test. The titanium hardness was lower than that of
tungsten, and serious wear occurred under the increasing
load, with a deep groove being formed. All the coatings
were deposited at various laser powers of (900, 1000 and
1200) W. The coating deposited at the laser power of
900 W showed an increment in the wear resistance. The
coating deposited at the laser power of 1000 W demon-
strated a higher wear rate than that deposited at the laser
power of 900 W. The further increase in the laser power
to 1200 W gave rise to a yet higher wear rate. This effect
of increasing the laser power can be attributed to the
distribution of the tungsten powder. The outcome
demonstrates that the samples were exposed to a sliding
N. NDOU, E. AKINLABI: MICROSTRUCTURE, WEAR RESISTANCE AND MICROHARDNESS OF W-PARTICLE- ...
272 Materiali in tehnologije / Materials and technology 52 (2018) 3, 269–274
Figure 6: Hardness profile for the deposition achieved with 1000 W
Figure 5: Hardness profiles of the composite coatings

action, which caused adhesive wear. Moreover, a number
of grooves and scars were seen on the worn surfaces of
the samples. The lower laser power resulted in less
unmelted carbide (UMC). With less UMC, the wear
resistance of the material is poor owing to the reduced
support effect of the Ti6Al4V/W powder.
30
The coatings deposited at the laser powers of
800–1200 W showed a lower wear volume contrasted to
the Ti6Al4V substrate and the coatings deposited at a
laser power of 1000 W. The wear resistance increased
due to the LMD process can be attributed to the distri-
bution of the W powder in the coatings.
Table 2 presents the wear volume at various laser
powers.
Table 2: Wear volume at various laser powers
Samples
Wear
volume
(mm)
Laser power 0.8 kW and scan speed of 0.7 m/min 0.144
Laser power 0.9 kW and scan speed of 0.7 m/min 0.0171
Laser power 1.0 kW and scan speed of 0.7 m/min 0.076
Laser power 1.1 kW and scan speed of 0.7 m/min 0.089
Laser power 1.2 kW and scan speed of 0.7 m/min 0.124
Substrate material 0.314
The laser power of 1000 W was observed to result in
the lowest percentage of the wear volume of 8 %. The
laser power of 900 W gave rise to a high wear-volume
percentage of 19 %. The breadth and length of the wear
track at the laser power of 900 W were greater than those
of all the other samples except the substrate. Table 2
demonstrates that the sliding-wear rate of the coating
samples deposited at various laser powers is lower than
that of the substrate. The substrate shows the highest
wear volume of all the samples.
4 CONCLUSIONS
This article reports onaWr e inforcement of the
Ti6Al4V alloy achieved by means of LDM. Different
laser powers were used, affecting the microstructure, and
the LMD process ensured the microhardness of the
Ti64l4V/W coatings. The hardness, microstructure, che-
mical analysis and wear behaviour of the coated material
were investigated. The findings of the study are as
follows:
• The LMD process is appropriate for achieving suit-
able bonding between the substrate and the cladding
area.
• The coated sample deposited at a laser power of
1000 W exhibits the maximum microhardness value
of 719 HV.
• The composite coating deposited at laser powers of
1000 and 900 W revealed no porosity or cracks in the
microstructure of most of the produced samples.
However, porosity was observed in the microstructure
obtained at a laser power of 1200 W.
• Tungsten particles enhanced the surface hardness of
the coated alloy, and the composite coated at the laser
power of 1000 W showed a higher wear resistance
than the coated samples produced at the laser powers
of 900 and 1200 W.
• The strength of the Ti6Al4V/W composites after the
LMD process was much higher than that of the
Ti6Al4V alloy. The wear resistance of the
Ti6Al4V/W composites was much higher than that of
the Ti6Al4V alloy.
Acknowledgments
The acknowledgement goes to the staff members of
the Tshwane University of Technology who assisted with
the laboratory equipment.
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274 Materiali in tehnologije / Materials and technology 52 (2018) 3, 269–274