CHAPTER 1

INTRODUCTION

1.1TRANSIENT LIQUID PHASE BONDING

Transient liquid phase (TLP) bonding is a relatively new bonding process that joins materials

using an interlayer. On heating, the interlayer melts and the interlayer element (or a

constituent of an alloy interlayer) diffuses into the substrate materials, causing isothermal

solidification. The result of this process is a bond that has a higher melting point than the

bonding temperature. It is capable of producing nearly invisible joints that have strengths and

other properties similar to the base metal.

PRINCIPLE

The main principle of the process is solid state diffusion into the material to be joined. The

process has been applied to several metallic systems but the concept is not limited to any

particular class of materials, but rather to systems whereby a chemical or other driving force

inherently leads to solid state equilibrium.

1.2 STEPS IN TLP BONDING PROCESS:

1. Setting up the bond

Bond setup usually consists of placing a thin interlayer between the substrates.

The interlayer can be in many different formats:

1. Thin foil

2. Amorphous foil

3. Fine powder

4. Powder compact

5. Brazing paste

6. Physical vapour deposition process

7. Electroplating

2. Heating upto bonding temperature to produce liquid in bond region

3. Holding the assembly at bonding temperature until the liquid has solidified

2

4. Homogenizing the bond at a suitable heat-treating temperature

The modes of heating in the above three stages can be:

1. Radiation

2. Conduction

3. Radio-frequency induction

4. Resistance

5. Laser

6. Infrared

1.3 PHASE DIAGRAM REPRESENTING THE PROCESS

Upon heating an interlayer of B rapidly dissolves the parent metal A until the composition at

CL is reached. Widening next occurs lowering the concentration of B in the liquid to CL.

Isothermal solidification then reduces the amount of liquid although the composition

remains constant at CL. Once solidification is complete, the maximum concentration in the

joint can be reduced from CL by homogenization.

Fig 2. Schematic of a binary eutectic phase diagram showing the stages in TLP bonding. [3]

3

1.4 STAGES

The TLP process has been divided into four stages by Tuah Poku et al[13] namely. Each

stage is shown in the figure 2.

1. Dissolution

2. Widening

3. Isothermal solidification

4. Homogenization

A fifth stage termed stage 0 has been shown to account for the effects during heating up to

bonding temperature.

1. Dissolution

A layer of pure metal B is sandwiched between a structure of metal A. Upon heating

to the bonding temperature the interlayer and parent metal undergo interdiffusion

to form a liquid phase. As the dissolution progresses, the liquid composition moves

from CL to CL. The time required for this step has been estimated to be on the

order of seconds. Therefore any MPD previously diffused would be remelted.

2. Widening

Upon the completion of the dissolution stage, the widening of the interlayer drives

the composition to the alpha rich liquidus at CL. The widening process requires

times on the order of minutes.

3. Isothermal solidification

This is the most important step as it requires the greastest amount of time and is

dependent on the width of liquid interlayer formed and the rate of diffusion into the

bulk. During this stage the diffusion of the MPD into the parent metal occurs at a

rate dependant on the diffusion constant in the bulk, provided there are no kinetic

restrictions at the interface.

4

4. Homogenization

Homogenization completes the process and is dependant on the time at

temperature. It is controlled by a solid state diffusion rate similar to other

homogenization processes. The homogenization time is a function of the required

maximum tolerable MPD concentration.

Fig 2. Four stages of TLP bonding. Stage 0 has been included to account for interdiffusion

occurring duing heat up. The grey shading indicates the concentration of MPD. The arrows

indicate the direction of movement of solid liquid interface.[2]

5

1.5 CLASSIFICATION OF TLP BONDING ON THE BASIS OF INTERLAYER

COMPOSITION

1. TYPE I

In type I processes the interlayer is a pure metal and hence is the MPD(melting

point dpressant). This type of interlayer requires all four stages including

interdiffusion with the parent metal before liquefying. The extent of widening is

maximized as the concentration of the MPD must be reduced from unity to

liquidus composition at CL.

2. TYPE II

In type II processes, an interlayer at or close to the liquidus composition is used.

In this case, only stage III and IV occur and the amount of MPD for a given initial

thickness is reduced. This approach used in superalloy TLP bonding, requires

bonding times on the order of minutes versus hours in the type I approach.

1.6 VARIANTS OF TLP BONDING

1. TEMPERATURE GRADIENT TLP BONDING

The application of a temperature gradient causes a non-planar bond interface which

tends to result in stronger bonds

2. WIDE-GAP TLP BONDING

Gaps of 100-500m can be bonded or repaired by the use of a melting and non-

melting constituent. This technique can also be used in conventional TLP bonding to

accelerate isothermal solidification.

3. ACTIVE TLP BONDING

A ceramic and metal can be joined by a multi-component interlayer in which atleast

one componenet reacts with the ceramic while another diffuses into the metal to

cause isothermal solidification

4. PARTIAL TLP BONDING

This technique is used to join ceramics. The interlayer consists of thin layers of low-

melting-point metals or alloys on each side of a much thicker refractory metal or

alloy layer.

6

1.7 APPLICATIONS OF TLP BONDING

TLP bonding is often used in high-stress, high-temperature applications where

brazing, welding, and diffusion bonding cannot be used for various reasons. The

requirement of metal systems suitable for TLP bonding must have stability at

elevated temperatures and high diffusion coefficient of MPD through the matrix.

This makes Ni based superalloys as the ideal metal for TLP bonding. The process has

been successfully applied to other metals as well.

1. Al-based alloys

2. Ti-based alloys

3. Ceramics

4. Dissimilar metals

5. Metal to ceramic

6. Fe based alloys

Table 1. APPLICATION TO Fe-BASED ALLOYS[1]

SUBSTRATE INTERLAYER

304SS Ni-Cr,304L SS, BNi-2

304L SS NB 51

Duplex SS Cu, Fe-B-Si, Ni-Si-B, MBF-30, MBF-35,MBF-50, MBF-80

Carbon steel Cu, Fe-B

Fe-Ni-Cr Ni-B-Cr-Si(various combinations)

Incoloy MA956 B,Fe-B-Si

Incoloy MA957 Fe-B-Si, BNi-1a, BNi-3

Low carbon steel Fe-B-Si, BNi-2

ODS(oxide dispersion strengthened) steel(Fe-Cr-W-YO-Ti)

Fe-Si-B

PM2000(Fe-Cr-Al) B, Fe-B-Si

T91 steel Fe-B-Si, Fe-Ni-Cr-Si-B, BNi-2

7

1.8 CHARACTERISTICS OF TLP BONDING

Table3. characteristics of TLP bonding process[1]

ADVANTAGES DISADVANTAGES

Base metal properties at joint Long bonding time (hours)

No interface remains after bonding Restricted to high temperatures,T/Tm=0.6

Self homogenizing Fast diffusers required preferable interstitial elements

Intermetallic formation can be achieved Rapid heat up required

Minimum suface preparation Close fit-up required

Large and complex shapes bonded simultaneously

Post bonding heat treatment for age hardening alloys is required

1.9 PARAMETERS

1. Interlayer thickness

2. vaccuum

3. fixturing pressure

4. Interlayer composition

5. Time

6. Bonding temperature

1. Interlayer thickness

Interlayer or foil thickness has a strong influence on the solidification time and

thereby productivity. Higher foil thickness creates higher volume of the liquid

metal which requires more time to solidify. Also it calls for more time required

for homogenization as large volume of the interlayer element has to be diffused

through the parent metal matrix. Therefore a minimum amount of foil thickness

should be the ideal case. It is clear from figure3., as the foil thickness is

decreased the minimum time required for isothermal solidification decreases.

The minimum in the bonding time arises due to the trade off between the

increase in the diffusivity and the amount of dissolution which also increases

with temperature. Over the range of permissible bonding temperatures, the

bonding time varies by less than an order of magnitude. Hence, a significant

reduction in bonding time can only be achieved by reducing foil thickness.

8

Fig3. Isothermal solidification time for TLP bonding of copper using a silver foil.[2]

The various values of interlayer thickness frequently used are shown in table 4 below.

Table 4. Common values of inter layer thicknesses used[1]

Thickness range(m) Common thickness(es)m

Frequency(%)

500 2

2. Vacuum

The bonding process is usually confined in a vacuum to avoid oxide formation.

Although an inert atmosphere, such as argon, can be used. The vacuum

pressures used in the experiments referenced in [1] are normally distributed

about 0.1 mHg (millitorr) with minimum and maximum values of 0.00015 and

34 mHg, respectively.

9

3. Fixturing pressure

A pressure is usually applied to the bonding assembly to keep the substrates

aligned and to promote bonding. Specific pressures are categorized in table 2 by

their nearest order of magnitude.

Table 2. fixturing pressures used during TLP bonding[1]

Nearest order Frequency (%)

1 kPa 8

10 kPa 5

100 kPa 16

1 MPa 36

10 MPa 31

100MPa 4

4. Interlayer composition

Use of different interlayers in terms of composition and form with different

metal systems has been by far the most widely experimented among all the work

that has been done on the transient liquid phase bonding. The process starts

from interlayer and ends at interlayer. The properties and reaction of interlayer

elements with that of the base metal determines the microstructure and other

properties of the TLP joint.

Requirements of interlayerMPD(melting point depressant)

Atleast one element of interlayer, MPD, must have solubility in the base metal.

The MPD must have a significant diffusivity at the bonding temperature to

ensure reasonable bonding times. Finally the elements in the interlayer must not

be detrimental to the physical and mechanical properties of the base metal.

It is desirable to have the interlayer composition as close to the liquidus at the

bonding temperature as possible. Taking two foil interlayers, one pure metal B

and the other an A-B alloy close to the liquidus composition. The amount of MPD

that must diffuse in the pure metal case is,

w(C-CL)grams/cm

10

where C, the initial concentration of the MPD, is unity for a pure metal

interlayer and W is the initial foil thickness. the solidification time, as presented

in [2] and derived by Tuah et al.[13] is,

t= { w( C/ CL)}/16D

which indicates that the bonding time varies as the square of the initial MPD

concentration and foil width. This equation illustrates the advantage of using

electroplated alloy interlayers which minimize both thickness and MPD

concentration.

If the MPD is a minor constituent of the interlayer and other constituents foran

an intermetallic with the parent metal, an increase in the bonding time will

result. In this situation, the MPD has to diffuse through the intermetallic. Since

diffusion in intermetallics is slow, the temperature must be raised above the

melting point of the highest melting intermetallic in order to achieve rapid

bonding times.

5. Time

Duration of the isothermal solidification stage to complete is the most important

to determine the overall bonding time of the process as it is the longest stage. If

the holding at bonding temperature is less than the time required for complete

solidification the left over liquid can solidify has brittle eutectic phase which can

be detrimental to the mechanical properties and the melting point of the

resultant bond and microstructure may not be as the intended one.

But the prediction of isothermal solidification time is a costly and time

consuming process. This is one of the reason why the process has not been

industrialized for mass application.

6. Temperature

The bonding temperature is dependent on the melting point of the interlayer. It

is always below the melting point of the base metal. Bonding temperature has to

be determined and selected in uniformity with the phase diagram to avoid any

intermetallic compound in the final joint.

Bonding temperature has a strong influence on the microstructure and thereby

mechanical properties of the joint. Increase in temperature causes an increase in

the diffusion coefficient.

11

CHAPTER 2

2.1 LITERATURE SURVEY

The work on TLP bonding of steels was the emphasis and basis for the present literature

survey done. Although the process of TLP bonding has been mostly applied to Ni based

super alloys but the process is suitable to other metal systems as well. Use of TLP bonding

process for joining similar and dissimilar steels and also steel with other metal system has

been attempted and has been successful. Present and future work would be directed to join

steel(similar or dissmilar). The effect of various parameters on the quality of joints obtained

and the productivity has been studied from the past work. Along with that few novel

methods for interlayer fabrication and modification to the process, such as, effect of plastic

deformation and two step heating process instead of one, were also studied.

The papers discussed in the present literature survey are grouped according to their

objective and parameter.

1. Interlayer thickness

As explained before less thickness leads to increase in productivity. But there is a

certain amount of minimum thickness that is required to avoid the pore formation in

the joint region.

N. S. Bosco et al.[3] demonstrated this on the Cu-Sn system. They suggested that such

pores are a consequence of the growth and subsequent contact of CuSn intermetallic

grains on the two surfaces to be bonded, prior to the formation of transient liquid

phase. Hence they proposed a criterion stated as the thickness of the interlayer must

exceed that which is consumed through solid state diffusion; otherwise, no liquid is

formed at the bonding temperature. This sets a minimal requirement on the interlayer

thickness.

2. Heating rate

N. S. Bosco et al.[3] demstrated that reductions in bonding time can be achieved

with increasing heating rate, because of the corresponding reductions in the

required interlayer thickness fig4. The resulting grain size was also larger with slow

heating rates fig5.

12

Fig 4. Effects of heating rate on the bonding time needed for complete consumption of the

intermetallics, leaving the Cu solid solution as the terminal phase.[3]

Fig5. SEM images of the coated and etched growth samples in plan view; (a) 2 K/min, (b) 5 K/min, (c) 15 K/min. [3]

13

Xuegnag Wang et al.[4] investigated the effect of two stage heating process on the

microstructure and the mechanical properties of TLP bonding of dissimilar steels. In this

method the samples were heated to a high temperature for short duration and then

solidified at low temperatures for longer duration in the isothermal solidification stage.

Table5. parameters used in TLP bonding[4]

sample Short-time heating stage Isothermal solidification stage

Temperature(C) Time (s) Temperature(C) Time (s)

1 1270 10 1250 120

2 1260 10 1240 120

3 1240 120

4 1240 10 1220 120

5 1220 10 1200 120

Figure 6. shows the cross-sections of TLP bonds made using conventional heating and the

two-step heating processes. A non-planar interface is observed in all the joints by

conventional heating and the two-step heating process. However, a planar interface is

also observed in the joint by conventional heating process.The curvature of the interface in

conventional TLP bond is smaller than that in two-step TLP bonds.

Some voids are found along the center line of the conventional TLP bond at 1240 1C (Fig.

6c). No voids are found in the two-step TLP bonds at the isothermal solidification

temperature of 1240C or above (Fig. 6a and b), and some voids are found under the

isothermal solidification temperature of 1240C (Fig. 6d and e).The voids in the two-step TLP

bonds depend on the short-time high temperature and isothermal solidification

temperature. The amount of voids is decreased with the increase of isothermal

solidification temperature during two-step TLP bonding which is evident from the figure 6.

14

Fig6. Optical micrograph of 45MnMoB-30CrMnSi dissimilar joints made using different heating processes: (a) sample 1; (b) sample 2; (c) sample 3; (d) sample 4. [4]

The observed mechanical properties were also better as compared to conventional TLP

bonding process because Voids are decreased and bending strength is increased.

Figure7. The mechanical properties of all the samples. (a) tensile strength and (b) bending

strength. [4]

15

3. TIME

H Noto et al.[5] investigated the effect of different holding times at bonding temperature of

9CrODS(oxide dispersion strengthened) steels using Fe-3B-2Si-0.5C filler, on elemental

distribution and nano-indentation hardness. The results were compared with 19CrODS steel.

They observed that chromium-boride needle-like precipitates, which induce

embrittlement, were absent in low Cr steel as is clear from fig. 8

Fig8. Maps of B and Cr distribution in the TLP bonding region for 30 min, 1180 C bonds in:

(a) 9CrODS steel, (b) high CrODS steel. [6]

It was observed that increase in holding time causes better diffusion and uniformity. From

the quantitative line analysis, shown in fig. 9, it is can be clearly seen that chromium-boride

peaks diminished as the holding time was increased from 0.5 to 4.0 h. Cr diffused into the

bonding zone and its content increased. B also diffused uniformly and Si had slow diffusion.

16

Fig. 9 Results of quantitative line analyses for various elements in 0.5 h and 4 h

bonds formed at 1180 C: (a) bonding zone, (b) DAZ, (c) parent alloy. [5]

As the holding time increases from 0.5 to 4.0 h the uniformity in hardness profile

occurs as the Cr boride phase present was diminished due to better diffusion of Cr.

This is observed from the hardness plot at various regions of the joint. Hardness

increased in the DAZ from the base metal value of 600mgf/m clearly denotes the

formation of hard and brittle phases.

Fig. 10 Nano-indentation hardness for bonding times of 0.5, 1.0 and 4.0 h at 1180 C,

without additional heat-treatment: (a) bonding zone, (b) DAZ, (c) parent alloy. [5]

17

4. TEMPERATURE

T Vigraman et al.[6] used TLP bonding to join AISI304L to low carbon steel with an

AISI304L interlayer at various temperatures for fixed holding time of 90min. It was

observed from the microstructure shown in fig. 11 that reaction zone thickness

increases with the temperature. Also coarse grains are observed due to higher

temperatures.

Fig. 11. Microstructures of bonded sample interfaces processed at temperatures (a) 850

C (SI), (c) 900 C (SII), (e) 950 C (SIII), the corresponding magnified images are shown in

the right hand side, namely, (b), (d), and (f). [6]

18

From the SEM images, fig. 12, the presence of voids and lack of diffusion at the interface

on account of low temperature was observed. An increase in the width of diffused

region occurred with increasing temperature. This increase indicates the diffusion of

increased amounts of elements such as Cr, Ni, Si and Mn towards the low carbon steel

when the temperature is increased.

Fig12. SEM micrographs (a and b) for sample SI, (c and d) for sample SII, and, (e and f) for

sample SIII[6]

19

An increase in temperature has a direct effect on hardness values due to higher diffusivity.

The reason may be the increase in the thermal activation and the migration of atoms from

either side of the diffusion couple. In the interface between low carbon steel and the

interlayer, the picking up of elements, namely, Cr, Ni, Mn, and Si, has been

observed due to the migration of atoms. Here, elements especially Cr, react with carbon and

form carbides, which increases the hardness of the other interface (interlayer and AISI 304L

base metal) due to carbon pick up and formation of carbides. Therefore, the hardness value

increases.

5. INTERLAYER COMPOSITION

S. J. Chen et al. [7] joined T91 steel pipes bys TLP bonding using 3 different

interlayers to find out the most suitable interlayer based on Fe-Ni-Si-B system. Based

on the properties of the joint obtained the the best interlayer has been identified.

The optimum process has been obtained with the result : bond made at 1250c for

3min under 6Mpa with FeNiCrSiB composite interlayer.

Table 6. Mechanical properties were observed [7]

Sanghoon Noh et al. [8] investigated the behaviour of TLP bonded ODS steel using

and amorphous insert material based on Fe-3B-5Si. They observed that bonding does

not affect nano-oxide morphology of base material. It was noted during the tensile

testing that Y-Ti-O precipitates at bonding interface triggers micro-cracks at joint

region with proceeding deformation and enhances ductile rupture.

Interlayer Temperature Tensile strength Bond strength Breaking position

BNi2 1225 358 100 Joints

Fe78Si9B13 1225 736 400 Joints

FeNiCrSiB 1250 780 679 Base metal

860 980 Base metal

20

Nicolas Di Luozzo et al.[9] joined carbon steel tubes using Cu interlayer and

compared with amorphous Fe-B-Si interlayer bonds. It was observed that the

process does not lead to completion throughout the width which is proved by the

presence of athermally solidified Cu rich phase as noted in fig 13.

Fig 13. microstructure of the JR for the TLPB using a Cu interlayer as obtained by FEG-SEM (Back

scattered electron mode). White contrast phase corresponds to ASL(athermally solidified

liquid). [9]

Hiroyuki Noto et al.[10] attempted to refine the grains of TLP bonded ODS steel by using a

newly developed ODS insert foil (Fe9Cr2W0.2Ti0.35YO0.5C3B2Si). The grains were

refined from 40m to 14m when compared with non ODS amorphous insert foil(F-B-Si-C)

which can be seen from the fig. 14.

The reason was attritubted to the coherency with the parent metal matrix. The coherency

(or inoherency) between the oxide particles and the matrix can be key to the quality of

bonding. The incoherency calculated by Bramfit equation was quite low compared with

other oxides and carbides. It is also considered that the oxide particles hinder the motion of

grain boundaries and suppress grain growth

21

Fig. 14 The microstructure of TLP bonding using (a) amorphous foil and (b) ODS foil. [10]

.

Xinjian Yuan et al. [11] devised a novel method of manufacturing iron-based interlayer

based on a duplex stainless steel and a MPD (B). The position of interlayer on the Schaeffler

diagram was selected very close to the base metal fig15. B content of 3.93% was selected in

view of the necessary difference required in melting point between base metal and

interlayer. Also higher B content leads to longer solidification and homogenization time as

can be seen from fig. 16.

It was noted that as the holding time increased from 60s to 1800s the presence of Cr boride

and B nitride reduces and was completely absent at 7200s.

22

Fig. 15 Positions of the selected interlayer, the duplex stainless steel base metal and the

bond zone in Schaefller diagram[11]

Fig. 16. change in the melting temperature of filler as a function of B concentration[11]

23

M. A. Arafin et al. [12] investigated the effect of alloying elements on isothermal

solidification during TLP bonding of SS410 (stainless steel) and SS321 using a BNi-2

interlayer. They used random walk modelling technique to model the diffusion coefficients

of the elements. Migrating solid/liquid interface modelling and solute distribution law were

used for the study of kinetics of isothermal solidification. The results were compared with

experimental data fig.17 . It clearly shows that the predicted time values are very close to

the experimental data.

Fig17. Comparison of predicted isothermal solidification times with different confidence

levels (modified migrating solid/liquid interface model) with experimental data for an initial

joint gap of 70m for (a) SS 410/BNi-2 and (b) SS 321/BNi-2. [12]

24

2.2 SUMMARY OF LITERATURE SURVEY TRANSIENT LIQUID PHASE

BONDING S

No.

AUTHOR TITLE MATERIAL SYSTEM CHARATERISTICS

1

Xinjian yuan et al. Microstructural

characteristics

in vaccuum tlp

alloyed

Duplex stainless

steel

1.method for making iron

based interlayer developed

2.JR was free from carbide

and nitride phases

2 M. Mazar Atabaki Microstucture

evolution in

partial tlp

bonding

Zircalloy-4 to ss321 1.active titanium filler used

2.Ti and Zr led to low

isothermal solidification and

proven that Cu has the same

effect

3 H. Noto el al. TLP of ODS

steels

ODS steels 1.sequential process for tlp

for 9CrODS steel confirmed

2.precipitation of Crboride

found in 19CrODS absent in

9CrODS steel

4 H. Noto et al. Grain

refinement of

tlp bonding

zone using ODS

insert foil

ODS martensitic

steel

1.ODS insert foil(Fe-9Cr-2W-

0.2Ti-0.35Y2O3-0.5Cr-3B-2S)

fabricated using spark plasma

sintering

2.grain size is one third of

conventional insert

3. hardness increased

5 M A Arafin et al. Effect of

alloying

elements on

isothermal

solidification

during tlp

SS410 and SS321

using BNi-2

interlayer

1.theorical isothermal

solidification time verified by

experiment

2.solubility of B for SS410

decreased by 0.3% at high

temp

6 S J Chen et al. Tlp bonding of

T-91 steel pipes

using

amorphous foil

T-91 steel with BNi2,

Fe78Si9B13 and

FeNiCrSiB

amorphous filler

1.microstructure and element

distribution examined

2.tensile and bend strength

with FeNiCrSiB eqtual to

substrate

3.fracture caused by brittle

intermetallics at interface

7 Nicolas Di Luozzo

et al.

Tlp of carbon

steel tubes

using Cu

interlayer:

characterization

and comparison

Carbon steel ,

interlayer pure Cu

1.Cu interlayer to led to

partial completion of bonding

2. cementite concentration

higher in JR with Cu

interlayers

3.tensile test specimen failed

25

with Fe-B-Si

interlayer

at HAZ and UTS same as BM

8 Waled M.

Elthalabawy et al.

Microstuctural

development of

diffusion brazed

joint

316L SS, magnesium

alloy(AZ31) and Ni

interlayer

1.double stage bonding

process used

2.B2 intermetallics formed

during diffusion brazing stage

and had detrimental effects

9 M. I Barrena et al. Interracial

microstructure

and mechanical

strength of

diffusion

bonded joint

WC-Co/90MnCrV8

cold worked tool

steel using Cu-Ni

interlayer

1.Maximum tensile strength

obtained confirms promising

technology

2. effect of bonding time and

temp on joint quality was

studied

10 T Vigraman et al. Diffusion

bonding

AISI304L to low

carbon steel using

AISI304L interlayer

1.fracture occurred at BM

low carbon steel

2.formation of brittle phases

at high temp

3. tensile strength of

340.5Mpa

11 M. Mazar Atabaki Partial transient

liquid phase

diffusion

bonding

Zr2.5-Nb to SS321

Interlayer- one

active Ti based and

two Zr based

1.infulence of bonding temp

and time on microstructre,

microhardness, shear

strength and interlayer

thickness

2.titanium based interlayer

has better wetting behavior

on Zr surface

3.increase in temp caused

reduction in wetting

properties

4. height of interlayer was

decreased on substrate by

increasing temperature

5. Ti based interlayer

prevented formation of

brittle intermetallics

12 R. Soltani Tashi Diffusion

brazing

Ti-6Al-4v and

austenitic ss using

silver based

interlayer

1.shear strength decreased

with increasing brazing temp

and time

2.increase in temp led to

formation of intermetallics

namely Cu-Ti and Fe-Cu-Ti

26

13 Hongsheng

Chen et al.

Effect of Ni

interlayer on

partial tlp

bonding

ZrSnNb and

304SS

1.a-Zr phases dispersedly

exist in reaction layer

2.reaction is larger than that

without Ni interlayer

14 Sanghoon Noh et

al.

Evaluation of

microstructure

and mechanical

properties of

liquid phase

diffusion

bonded ODS

steels

ODS ferritic steel

and interlayer Fe

3B5Si

1.ODS showed homogeneous

distribution of insert material

2. YTiO precipitation

occurred upto 20micron

3.tensile strength 90% of BM

4.poor elongation and impact

fracture energy

15 T.I. Khan et al. Effect of tlp

bonding

variables on

properties of

micro duplex

steel

2205 micro duplex

SS and interlayer

pure copper and foil

based on the Fe-Si-B

1.rapid cooling and heating

suppressed formation of

sigma phase

2.mechanical and corrosion

properties similar to that of

parent alloy

16 T. Padron Modeling the

tlp bonding

behavior of

duplex SS using

Cu interlayer

Duplex SS and cu as

interlayer

1.analytical and experimental

results were compared

2.lattice and grain boundary

diffusion through alpha phase

played an imp role

3. model for homogenization

stage deviates from

experimental results

17 A.H.M.E. Rahman Tlp bonding of

commercially

pure iron using

Cu and Ag based

interlayer

Interlayer Cu-

25micron

Interlayer Au12Ge

100micron

1.Cu did not diffuse

completely in BM

2.the Au layer diffused

almost completely except

some region

3. UTS with Cu-291Mpa and

with Au 315Mpa

18 Xuegang Wang et

al.

Effect of two

step heating

process on joint

microstructure

and properties

during tlp

bonding of

dissimilar

metals

45MnMoB and

30CrMnS

1.short time high temp

heating followed by low temp

isothermal solidification

2.two step process changes

interface morphology from

planar to non planar

3. voids are decreased and

bending strength is increased

19 Nicolas Di Luozzo Microstructure Carbon steel tubes 1.JR- ferrite, HAZ and BM

27

et al. and mechanical

characterization

of steel tubes

joined by tlp

bonding using

an amorphous

layer

and interlayer based

on Fe-Si-B

cementite and ferrite

2. tubes failed away from the

bond at HAZ and ultimate

tensile strength 96% of BM

20 H.M. Hdz-Garca

et al.

Effect of Si nano

particles on tlp

bonding of 304

SS

304 SS with

interlayer BNi-9

1.Si nano particles act as

MPD

2.Si induces the dissolution of

filler metal

21 M. Mazar Atabaki

et al.

TLP bonding of

SS304

SS304 with Cu

interlayer

1.intermetallic compound

2. elemental distribution

22 N.S. Bosco et al. Critical

interlayer

thickness for

TLP bonding in

Cu-Sn system

Base metal-Cu

Interlayer- Sn

1.benefits of high heating

rate on bonding time and

critical interlayer thickness

23 Hong Li et al. TLP bonding of

steel sandwich

panel under

small plastic

deformation

Interlayer- pure Cu

foil

1.lower solidification time

28

CHAPTER 3

METHODOLOGY

3.1GAPS

1. Practically no work has been done to study the effect of fixturing pressure.

2. So far there has been no work on the TLP bonding using interlayer in the form of

electroplated film which may be helpful in the reduction of solidification time

3. Evaluation of critical interlayer thickness for steel system and to study the

dependence of it on various forms of an interlayer

4. No work has been done on the fatigue and creep behaviour of the TLP bonded joints.

3.2GENERAL OBSERVATIONS

1. Interlayer coherent with the parent metal matrix gives better results in terms of

homogeneity and mechanical properties

2. MPD such as B, Si, Cu are quite commonly used for steel system

3. Boron as the MPD(melting point depressant) has the best diffusivity in steel

4. Holding for less durations than the required isothermal solidification time results in

athermally solidified liquid and poor mechanical properties

3.3PROBLEM FORMULATION

1. Steel used at high temperature such as in the nuclear application where high creep

strength is needed will be selected. The effect of different forms and composition of

interlayers on the creep strength is proposed to be investigate and thereby selection

of best interlayer for the selected steel.

2. Dissimilar steels will be selected and effect on their creep properties using different

interlayers is proposed to be investigated.

3.4OBJECTIVES 1. Selection of steel

2. Identification of the various interlayers to be used.

3. Selection of proper parameters

4. Characterization of the samples

5. Analysis of the results obtained

29

REFERENCES [1] Grant O. Cook III and Carl D. Sorensenoverview of transient liquid phase and partial

transient liquid phase bonding J Mater Sci (2011) 46:53055323

[2] W. D. MacDonald and T. W. Eagar Transient Liquid Phase Bonding Process, Material

Science of Joining

[3] N. S. Bosco, F. W. Zok,critical interlayer thickness for transient liquid phase bonding in

the Cu-Sn system Acta Materialia 52 (2004) 29652972

[4] Xuegang Wang , Xingeng Li ,effect of two-step heating process on joint microstructure

and properties during transient liquid phase bonding of dissimilar materials Materials

Science & Engineering A 560 (2013) 711716

[5] H. Noto , S. Ukai, S. Hayashi,transient liquid phase bonding of ODS steels Journal of

Nuclear Materials 417 (2011) 249252

[6] T. Vigraman , D. Ravindran ,diffusion bonding of AISI 304L steel to low carbon steel

with AISI 304L interlayer Materials and Design 34 (2012) 594602

[7] S.J. Chena, H.J. Tang, X.T. Jing,transient liquid-phase bonding of T91 steel pipes using

amorphous foil Materials Science and Engineering A 499 (2009) 114117

[8] Sanghoon Noha, Ryuta Kasadab et. al evaluation of microstructure and mechanical

properties of liquid phase diffusion bonded ODS steels, Fulsion Engineering and Design

85 (2010) 10331037

[9] N. Di Luozzo, Michel Boudard,Transient liquid phase bonding of carbon steel tubes

using a Cu interlayer: Characterization and comparison with amorphous Fe-B-Si

interlayer bonds et al., Journal of Alloys Comp. (2013)

[10] D Hiroyuki Noto , Ryuta Kasada , grain refinement of transient liquid phase

bonding zone using ODS insert foil, Journal of Nuclear Materials 442 (2013) S567

S571

[11] Xinjian Yuan , Chung Yun Kang,microstructural characteristics in vacuum TLP bonds

using a novel iron-based interlayer based on duplex stainless steel base metal alloyed

with a melting-point depressant Vacuum 99 (2014) 12-16

[12] M.A. Arafin, M. Medraj ,effect of alloying elements on the isothermal solidification

during TLP bonding of SS410 and SS321 using a BNi-2 interlayer, Materials Chemistry

and Physics 106 (2007) 109119

[13] Tuah-poku, I., Dollar, " A study of the transient liquid phase bonding process applied

to a Ag/Cu/Ag sandwich joint". Metallurgical Transactions A. 19(A) (1988), 675-686

30

Contents CHAPTER 1 .............................................................................................................................................. 1

INTRODUCTION ................................................................................................................................... 1

1.1TRANSIENT LIQUID PHASE BONDING ............................................................................................ 1

1.2 STEPS IN TLP BONDING PROCESS: ................................................................................................ 1

1.3 PHASE DIAGRAM REPRESENTING THE PROCESS .......................................................................... 2

1.4 STAGES ......................................................................................................................................... 3

1.5 CLASSIFICATION OF TLP BONDING ON THE BASIS OF INTERLAYER COMPOSITION ..................... 5

1.6 VARIANTS OF TLP BONDING ......................................................................................................... 5

1.7 APPLICATIONS OF TLP BONDING .................................................................................................. 6

1.8 CHARACTERISTICS OF TLP BONDING............................................................................................ 7

1.9 PARAMETERS ................................................................................................................................ 7

CHAPTER 2 ............................................................................................................................................ 11

2.1 LITERATURE SURVEY ................................................................................................................... 11

2.2 SUMMARY OF LITERATURE SURVEY TRANSIENT LIQUID PHASE BONDING................................ 24

CHAPTER 3 ............................................................................................................................................ 28

METHODOLOGY ................................................................................................................................ 28

3.1GAPS ............................................................................................................................................. 28

3.2GENERAL OBSERVATIONS ............................................................................................................ 28

3.3PROBLEM FORMULATION ............................................................................................................ 28

3.4OBJECTIVES .................................................................................................................................. 28

REFERENCES .......................................................................................................................................... 29