PPT Includes physical Metallurgy for Titanium and its alloys, Weld ability of them and two welding processes : GTAW and EBW. PPT also describes the Problems with the Welding of Titanium and alloys.

1. Prepared by Guides
Raghavendra Darji(385) Dr. S.N.Soman
M.E.-Part-I Dr. J.Krishnan
(Welding Tech.)
Metallurgy and Material Science Department,
Faculty of Technology and Engineering,
The M.S.University, Baroda.
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2.  Introduction
 Physical metallurgy of Ti
 Why we need to weld Ti ?
 Obstacles in the Ti welding.
 Weld ability of Ti alloys.
 Welding processes for Ti alloys.
 Gas Tungsten Arc Welding
 Electron Beam Welding
 References.
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3.  Name: Titanium
 Symbol: Ti
 Atomic Number: 22
 Atomic Mass: 47.867 amu
 Melting Point: 1660.0 °C
 Boiling Point: 3287.0 °C
 Number of Protons/Electrons: 22
 Number of Neutrons: 26
 Classification: Transition Metal
 Crystal Structure: Hexagonal
 Density @ 293 K: 4.54 g/cm3
 Year of Discovery: 1791
 Discoverer: William Gregor
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4.  Pure Titanium has closed pack
closed pack hexagonal crystal
structure (alpha phase) up to 16250
F,
Above this it goes to allotropic change
to BCC cubic structure known as
beta phase
 According to the phases present
Ti alloys can be differentiate into
Four different categories:
 Commercial pure Ti
 Alpha
 Alpha-Beta
 Beta
Aluminium Chromium Zirconium
Tin Copper
Iron
Manganese
Molybdenum
Nickel
Tungsten
Vanadium
Oxygen Hydrogen
Nitrogen
Carbon
Substutuional alloying
Interstitial alloying
Neutral
Beta phase
stabilizer
Alpha phase
stabilizer
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5. 5

6.  Titanium is 45% lighter than the steel(ASTM A36), while 60% heavier than
Aluminium(6061-T6),
 But most importantly it has the strength almost three times of the either of above two
alloys.
 Titanium has “ THE HIGHEST STRENGTH TO WEIGHT RATIO”.
 Titanium has the ability to passivate, and thereby exhibits a high degree of immunity
to attack by most mineral acids and chlorides.
 The combination of high strength, stiffness, good toughness, low density, and good
corrosion resistance provided by various titanium alloys at very low to moderately
elevated temperatures allows weight savings in aerospace structures and other high-
performance applications.
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7.  General corrosion is characterized by a relatively uniform attack over the
exposed surface of a metal. When titanium is in the fully passive condition,
corrosion rates are typically much lower than 0.04mm/y
 Titanium also forms oxide layer of Titanium dioxide(TiO2 ) on the surface this
layer is passive and impervious.
 Titanium alloys generally exhibits superior resistance to crevice corrosion
as compared to stainless steel and nickel-base alloys(<700
C). Pitting
corrosion is generally not of concern for titanium alloys.
 The coupling of titanium with dissimilar metals usually does not accelerate
the corrosion of titanium. The corrosion potential of titanium under normally
passive conditions is quite noble, but similar to stainless steel or nickel-base
alloys in the passive condition.
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8.  Titanium and other reactive metals react rapidly at temperatures well below
the melting point with all gases except inert gases.
 Contamination by dissolving oxygen and nitrogen from the atmosphere in
the weld pool results in an increase in tensile strength and hardness and
reduction in ductility.
 As a result even welds which have been effectively shielded show some
hardness increase across the fused zone, so ductility of joint will reduced.
 Thus the degree of ductility of the completed fusion weld depends upon the
effectiveness of the gas shielding.
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9. Effect of contamination in
argon gas
Effect of interstitials on
elongation and hardness
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10.  Unalloyed Titanium and most of
the alloys can be weld with the
same equipment and procedures
as for the austenitic stainless
steel and Nickel alloys.
 Ti alloys are rated according to
their ability to produce tough,
ductile welds in them
 The table shows the weld ability
of some of the Ti alloys
A=Excellent
B=Fair good
C=limited to special application
D=not recommended for welding
ELI=Extra Low Interstitial
Rating
A
A
B
A
A
A
B
B
A
C
D
B
Ti-6Al-4Zr-2Mo-2Sn
Alpha-Beta alloys
Ti-6Al-4V
Ti-6Al-4VELI
Ti-5Al-2.5SnELI
Near alpha alloy
Ti-8Al-1Mo-1V
Ti-6Al-2Cb-1Ta-0.8Mo
Beta alloy
Ti-13V-11Cr-3Al
Alpha alloys
Ti-7Al-4Mo
Ti-8Mn
Ti-0.2Pd
Ti-5Al-2.5Sn
Alloy
Commercial pure grade
Weldability of Ti alloys
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11.  Gas Tungsten Arc Welding
 Electron Beam Welding
 Gas Metal Arc welding
 Friction Stir Welding
 Resistance Spot Welding
 Laser Beam Welding
 Plasma Arc Welding
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12.  In general Titanium can be welded
using GTAW technique similar to
stainless steel, however there are
some fundamental differences.
 Ti at temp. Above 8000
C loses its
oxidation resistance and absorb
oxygen, nitrogen and hydrogen.
Enrichment of these elements
embrittles the weld metal and the
surface of heat affected zone.
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13.  Surface preparation is the most critical and important for the welding
 Titanium comes under the highly reactive metals, have high affinity toward
the Oxygen, Nitrogen and Hydrogen.
 Some procedures require that the filler wire be cleaned immediately before
use.
 The use of an acetone-soaked, lint-free cloth serves to assess surface
contamination caused by the die lubricant used in the wire drawing operation,
in addition to cleaning the filler wire. Pickling in nitric-hydrofluoric acid solution
is also used for cleaning.
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14. 1. Immersion in ethyl methyl ketone.
2. Scrubbing with lint free cloth.
3. Pickling in 3-4%HNO3+3%HCl+63% water solution at
1000
C for 3 minutes.
4. Water cleaning.
5. Cleaning in ethyl methyl ketone.
6. Drying with lint free cloth.
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15.  DCEN polarity is used for the Ti welding generally. because deeper weld
penetration and a narrower bead can be obtained than with direct current
electrode positive (DCEP).
 Also, in manual welding, DCEN is easier to control. DCEN produces the
greatest amount of heat at the work piece , it offers the advantages of deep
joint penetration and faster welding speeds.
 The conventional Thoriated tungsten types of electrodes (EWTh-1 or
EWTh-2) are used for GTAW of titanium. Electrode size is governed by the
smallest diameter able to carry the welding current.
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16.  Ti filler metal selected to match the composition of the base metal. However
corrosive environment or high temperature services may dictate the use of
non matching filler metals.
 Sometimes the unalloyed Titanium filler are used to weld Titanium alloys
(Ti-5Al-2.5Sn and Ti-6Al-4V), that is to improve the ductility and toughness
of the weld.
 The use of unalloyed filler metals lowers the beta content of the weld ment,
thereby reducing the extent of the transformation that occurs and improving
ductility.
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17.  Molten Ti reacts strongly with practically all materials including refractories
and carbon. The reaction impair the corrosion resistance , ductility and
toughness of the weld.
 Arrangement should be made for pre and post purge of shielding gas
through the torch before arc initiation and after the arc is broken, unless the
welding is over in the glove box.
 The type of shielding gas used affects the characteristics of the arc.
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18.  As a shielding gas we can use only two gases Argon or Helium. Sometimes
75% argon+25% Helium is also used. This will give arc stability along with
deeper penetration.
 Argon gives low gas flow rate minimizes turbulence and air contamination of
weld; improved heat-affected zone.
 Helium Better penetration for manual welding of thick sections (inert gas
backing required to shield back of weld against contamination).
 High gas flow rate may cause turbulence and thus contamination of the
weld.
 Trailing gas shield to provide additional protection to the hot cooling weld
metal is found necessary for good quality welds particularly when
mechanised welding with higher welding speed is employed.
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19.  Figure shows the arrangement for
the shielding gas for GTAW for
Titanium alloys in air with the
backing gas outside a weld
chamber welding.
 Backing gas is required to shield
the weld ment until its temperature
goes below 5000
C.
 At temperature above this
Titanium have high affinity for the
interstitials , they will ultimately
decrease the ductility and
toughness of the weld.
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20.  Most titanium weldments are stress relieved after welding to prevent weld
cracking and susceptibility to stress-corrosion cracking in service.
 Stress relief also improves fatigue strength.
 Stress Relieving needs to be carry out in an inert atmosphere.
 For unalloyed titanium and alpha titanium alloys, time and temperature
should be controlled to prevent grain growth.
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21. 21

22.  ELECTRON-BEAM WELDING (EBW) is a high-energy density fusion
process that is accomplished by bombarding the joint to be welded with an
intense (strongly focused) beam of electrons that have been accelerated up
to velocities 0.3 to 0.7 times the speed of light at 25 to 200 kV.
 Conversion of Kinetic energy into thermal energy causes the melting of
weld seam interface.
 Quality of the weld is equal or superior that of the GTAW.
 Power density is very high with EBW. So we can get low heat input in this
process.
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23. 23

24.  The electron beam is required to reach the work piece placed in a welding
chamber.
 If the electrons are projected into the normal atmosphere they lose all their
energy in collisions with atoms or molecules of oxygen and nitrogen.
 The vacuum requirement may often be as low as 10-7
torr that of the
standard atmospheric pressure. To achieve this two pumps are used
mechanical pump and diffusion pump.
 Depending upon the vacuum this process can be divide into three
categories,
1. High vacuum
2. Medium Vacuum
3. Low vacuum
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25.  Tungsten filaments are generally employed because of their high melting
point and high work function and also tungsten is less sensitive to
contamination.
 As a heating current DC is preferred because the magnetic field created by
the heating current can influence the direction of the beam.
 The coiled tungsten filament is heated to about 23000
C by passage of the
heating current. At this temperature the filament emits about 6*1018
electrons per second for each square centimetre of filament area.
 The speeds of the accelerating electrons in the electrons in the electron
beam range between 50000 to 200000 km/second depending upon the
accelerating voltage.
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26.  Basic variables employed for controlling the results of an electron-beam
weld include:
1. accelerating (applied gun) voltage,
2. beam current,
3. welding (beam spot travel) speed,
4. focusing current, and
5. standoff (gun column assembly to work piece) distance.
 Increasing the accelerating voltage or beam current increases the depth of
penetration.
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27.  ASSEMBLE AND PREPARE WORK AND FIXTURES FOR WELDING.
THIS INCLUDES CLEANING AND MAY INCLUDE DEMAGNETIZING,
PREHEATING, AND TACK WELDING.
 LOAD FIXTURED WORK ONTO WORKTABLE OR WORK-HOLDING
MECHANISM IN WELDING CHAMBER.
 START CHAMBER PUMPDOWN.
 AFTER CHAMBER PRESSURE HAS BEEN REDUCED TO 0.013 TO 13
PA (10-4 TO 10-1 TORR), FOCUS ON A TARGET BLOCK AND SET
BEAM PARAMETERS.
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28.  ALIGN JOINT TO THE BEAM POSITION, USING VERY LOW POWER
BEAM SPOT.
 BEGIN WELDING; THIS USUALLY IS PERFORMED AUTOMATICALLY,
BUT CAN BE PERFORMED MANUALLY.
 TERMINATE THE WELDING CYCLE.
 ALLOW WORK TO COOL SUFFICIENTLY IF MADE OF REACTIVE
MATERIAL, THEN ADMIT AIR TO THE CHAMBER AND REMOVE
FIXTURED WORK.
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29.  EBW is able to make weld deeper and narrower than the conventional arc
processes, with the low heat input it gives narrow work piece heat-affected
zone (HAZ) and noticeably fewer thermal effects on the work piece.
 In EBW, a high-purity vacuum environment can be used for welding, which
results in freedom from impurities such as oxides and nitrides.
 Total energy conversion efficiency of EBW is approximately 65%, which is
slightly higher than so-called conventional welding processes and much
higher than other types of high-energy-density welding processes, such as
laser-beam welding
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30. 1. Welding handbook, seventh edition, Volume.
2. www.millerwelds.com
3. Ti and its alloys as key materials for corrosion protection engineering
4. J.F.Lancaster “The Metallurgy of Welding, Brazing and Soldering”, Page
no:240-241.
5. ASM HANDBOOK Volume=6, welding, Brazing and soldering.
6. Welding processes and Technology, R S Parmar.
7. Proceeding for the international welding conference VOLUME-I.
8. AWS welding Handbook Volume 2, eight edition.
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