IRJET- Examination of Hardness Values for Ti-6Al-4V Welded Specimens and Micro Structural Characterization of Fractured Specimens

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 05 Issue: 12 | Dec 2018 www.irjet.net p-ISSN: 2395-0072
© 2018, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 371
EXAMINATION OF HARDNESS VALUES FOR Ti-6Al-4V WELDED
SPECIMENS AND MICRO STRUCTURAL CHARACTERIZATION OF
FRACTURED SPECIMENS
K.VENKATA SUBBAIAH1, K.BRAHMA RAJU2 SRINIVASAREDDY VEMPATI3
1Professor, Department of Mechanical Engineering, A.U College of Engineering (A), Andhra University Visakhapatnam,
Andhra Pradesh, India
2Professor, Department of Mechanical Engineering, SRKR Engineering College, Bhimavaram, Andhra Pradesh, India
3Assistant Professor, Department of Mechanical Engineering, QIS College of Engineering & Technology, Ongole, ,
Andhra Pradesh, India
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Abstract:- The main objective of the present
investigation is to examine the viability of Ti6Al4V welded
joints and evaluating hardness of different weld beads at
different zones using Vickers hardness tester which shows
impact on strength of the weld joint. Fractured specimens
are made in to 10mm x10mm size to analyze the structure
under Scanning Electron Microscope (SEM).the major
observation after SEM analysis is large number of crack
initiation sites are examined for more stress value.
Titanium welded joints are majorly used in industries like
aeronautical because it is having good mechanical, physical
and chemical properties. When compared to steel the
weight to strength ration of ti6al4v is high. Temperature
behavior and corrosion are two important good factors of
titanium material application [1-2] Ti grade 5 are used in
biomedical purpose because of light weight material and
non corrosion Jing Liu et al [3]. Identified the importance
of microstructure when
1. INTRODUCTION
Ti6al4v joint undergo fatigue loads, Torkamany et al. [4]
observed that porosity of welded region is focused when
titanium weld joints undergo pulse laser welding.
Xiao-Long Gao et al [5]. Examined microstructure and
porosity of Laser welded sheets of Ti6Al4V and informed
that presence of lamellar structure leads to increase in
resistance of growth of fatigue crack and identified the
presence of residual stress which are acting tensile mode.
When compared to TIG or electron beam welding Q.
Yunlian et al [6] observed more advantage in LBM because
of thin line of weld and with fine grain micro structure.
W.A. Baeslack et al practically observed that, Tungsten
inert gas welding is best method for titanium alloy and in
sheet form and micro structure observation is very clear
[7].
Different combinations of process parameters were
adopted. Bead geometry and micro hardness
characterization of samples cross section were studied.
Two tensile strength tests for each welding condition were
performed in order to evaluate the mechanical properties
of the welds. The mechanical properties of welds and the
parent metal were compared. The fracture surfaces were
studied by an electronic microscope.
2. EXPERIMENT PROCEDURE
The specimens consist of a main plate and two cross
plates. Size of the main plate 100mm x24mmx 6mm and
each cross plate 100mm x 24mm x 6mm. Subsequently, the
Fillets were made between the flange plate and cross plate
laying weld metal TIG welding process with corresponding
weld metal consumable.
2.1 Ultrasonic testing
Ultra sonic testing was done to all specimens for knowing
the defects in welded joints, few specimens were rejected
as we identified the cracks in welded regions and
specimens which are not having any defects are undergone
tensile testing and fatigue testing.
Fig 1 .Ultrasonic Equipment

2.2 Hardness Measurement
Hardness is the measure of resistance offered by the
material for the local compressive load. It consists of a
diamond indenter, in the form of a right pyramid shape
with a square base and angle between the opposite faces is
1360. The indentation is shown in Fig. b. For calculating
Vickers Hardness Value (HV), the distance between
diagonal corners has to be measured. The Vickers
hardness number is the ratio of the load applied in kg to
the area of the sloping surface of indentation in square
mm.
Fig 2. Vickers Hardness Equipment
Fig.3 Profile of Vickers Hardness measurement
2.3 Hardness values for welded specimens
The Vickers method depends upon micro hardness test
and macro analysis of specimen using optical
measurement system, ASTM E-384 a range loads are used
with help of diamond indenter to make an indentation and
to obtain a hardness value for Measuring Vickers
Hardness, Micro Hardness Tester is used Shimadzu Model:
HMV-G is used as per ASTM E 340-15 & IS:1501-13. A load
of 1 KG was applied on the specimens;
A minimum of five indentation diameters was used as
distance between the measurements. The hardness
profiles presented are an average of 3 profiles across the
welds at different depths as shown in Figure the micro
hardness value of as received, as welded Ti-6Al-4V shown
in. The value of micro-hardness for the base material of Ti-
6Al-4V is nearer to 339 ± 2.1 HV. The change in the
hardness is less at the BM area for the as welded specimen,
while there was a small decrease in the hardness of the BM
area after welding. It is observed that the hardness of the
FZ and HAZ of the cruciform welded Ti-6Al-4V concave
shape is around 365 ± 4 HV and 334 ± 5 HV.and hardness
of the FZ and HAZ of the convex shape is around 438 ± 5
HV and 359 ± 6 HV. HAZ and FZ of the Flat shape is around
259 ± 3 HV and 280 ± 3 HV.
Table.1. The micro hardness values of the Ti6al4v of
different weld bead shapes at different zones
Fig 4. Distribution of hardness values
Distance
from
weld
centre in
mm
Concave
Weld
Specimen
Convex
Weld
Specim
en
Flat
weld
specime
n
BM
-8 300 320 340
-7 314 341 342
-6 315 336 335
-5 366 435 279
HAZ
-4 363 443 284
-3 358 438 280
-2 327 359 259
FZ
-1 334 365 257
0 315 355 263
1 326 367 254
HAZ
2 334 361 256
3 361 437 278
4 369 441 281
BM
5 365 434 277
6 335 336 332
7 310 340 329
8 298 318 337

2.4. Tensile testing of specimens
The tensile strength of Welded material depends upon
Hardness value at different region. This test was will help
to predict the failure of welded joint priorly and there is
necessity of testing of specimen.
Fig 5. Specimen loaded in UTM machine
Specimen was failed at ultimate point of 890 Mpa (i.e 133
KN and area of cross section 144mm2) and the yield point
is 820MPa. Stress is applied on specimen with a range of
80%, 60%, 50% and 30% of yield point. Specimen was
broken out at outside of weld
Fig 6. Computerized graph for Tensile Testing of
specimen
3. OBSERVATION OF MICROSTRUCTURE OF SPECIMENS
FAILED UNDER TENSILE TESTING
Etching procedures were used to expose the underlying
micro structural features including grain boundaries,
inclusions, cracks, and secondary phases. Solutions that
can be used for etching titanium include: 100 ml water, 2
ml HF, 5 ml HNO3 (Krolls Etch)); or 20 ml water, 10 ml
40% KOH, 5ml 30% H2O2; or 30 ml glycerin, 10 ml Hf, 10
ml HNO3. The polished metallographic mount can be
immersed or swab etched in the solution from 3 to10
seconds to reveal the micro structural features.
The fractured surfaces of fatigue specimens were viewed
under SEM to identify fracture morphology. Scanning
electron microscopy is done to examine the surfaces of
fractured fatigue specimens and tensile specimens of
different welded samples at various magnifications and to
understand the mode of fracture. The fractured tensile
and fatigue samples are first cut to required size of (10mm
x10mm) and are then ultrasonically cleaned and degassed
before loading then in the SEM chamber.
SEM is a powerful tool for examining and interpreting the
microstructures of materials and is widely used in the field
of material science. The principle of SEM is based on the
interaction of an incident electron beam and the solid
specimen. SEM images were used for the evaluation of the
morphology of material.
Fig 7. Samples placed in SEM Equipment
Fig 8. Micro structure of Base Metal(Ti64)
Fig.9 Welded region of specimens indicates that there
are no under cuts, no crack initiation sites

In the present research micrographs were taken using a
SEM. A scanning electron microscope (SEM) is a type of
electron microscope that images a sample by scanning it
with a beam of electrons in a raster scan pattern. The
electrons interact with the atoms that make up the sample
producing signals that contain information about the
sample's surface topography, composition, and other
properties such as electrical conductivity.
The electron beam, which typically has an energy ranging
from 0.2 keV to 40 keV, is focused by one or two condenser
lenses to a spot about 0.4 nm to 5 nm in diameter. The
beam passes through pairs of scanning coils or pairs of
deflector plates in the electron column, typically in the
final lens, which deflect the beam in the x and y axes so
that it scans in a raster fashion over a rectangular area of
the sample surface
Fig 10.SEM analysis of fracture surfaces of different
weld bead shapes under tensile testing
Figure 11 a reveals the formation of ductile mode failure
with dimples of fine size and it is obvious that the fracture
surfaces of tensile tested sample of concave weld joint
show trans-granular fracture mode and the parallel
aligned finer dimples with grain boundaries are observed.
A typical Stage I fatigue fracture is observed in welded
joint (Fig 11 b). Stage I fatigue fracture surfaces are faceted
and often look like cleavage, and do not display fatigue
striations. Stage I fatigue is usually observed on high-cycle
low-stress fractures and is often absent in low cycle high
stress fatigue.
The direction of crack initiation is indicated by arrow mark
(Fig.11 c) obviously reveals the presence of transgranular
facets with some secondary cracking. The tensile fracture
surfaces exhibited in above figure indicate crack in a
ductile mode, coarse grain sizes are observed and Micro
voids and micro cracks are identified.
4. CONCLUSION
Vickers hardness measurements found that convex
specimens are having more hardness values. Hardness
values of specimen shows more impact on tensile strength.
In this work microstructure variation on fractured
specimens obtained from tensile test is studied. Further,
the fractured surfaces are checked through Scanning
electron microscopy to identify the modes of
failure/fracture. Porosities were observed in few
specimens, which affect the elongation and leads to
rupture of the specimen. Fracture analysis of the TIG
welds exhibited ductile fracture modes, with the high
proportion of ductile fracture in the presence of micro
cavities and cleavage areas, Because of high heat input in
TIG welding the formation fine grains is not possible which
leads to inferior fatigue performances of cruciform shape
welded joints, and convex weld specimens are exhibiting
good performance under fatigue testing
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[4] Torkamany, M.J., Malek Ghaini, F., Papan, E., Dadras, S.,
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IRJET- Examination of Hardness Values for Ti-6Al-4V Welded Specimens and Micro Structural Characterization of Fractured Specimens

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