[IJET-V1I5P3] Authors :Sadu Venkatesu , R. Saxena , P.K. Chaurasia , R. Ravi kumar , S. Murugan and S. Venugopal

International Journal of Engineering and Techniques - Volume 1 Issue 5, Sep-Oct 2015

ISSN: 2395-1303 http://www.ijetjournal.org Page 20

Optimization of Process Parameters on Bi-metallic Joints

Developed by High Temperature Nicrobrazing, Laser and GTAW

Joining Processes Sadu Venkatesu

1, R. Saxena

1, P.K. Chaurasia

1, R. Ravi kumar

1, S. Murugan

1 and

S. Venugopal1

1Metallurgy and Materials Group (MMG)

Indira Gandhi Centre for Atomic Research (IGCAR)

Kalpakkam- 603 102, Tamilnadu, India

1. INTRODUCTION

Fig.1 shows the schematic of parent metal geometry,

it has been used for all the joining methods, were

discussed in this paper. Tube(SS 316) and End plug

(SS 316L) were joined by GTAW, Laser and

Nicrobrazing joining processes, here we have

provided a gap of 50 microns for filling brazing

filler metal [1-3]. Brazing can be performed, where

Laser and GTAW welding processes are difficult to

carry out(thin-walled joints). However the hardness

value will be vary in joining processes. Helium leak,

metallographic and micro hardness properties were

tested. The results have been briefly discussed in

this paper.

II. MATERIALS

Table-1 shows the materials used and their

composition.

Fig.1 Schematic of parent metal geometry

RESEARCH ARTICLE

Abstract: A study on AISI 316 stainless steel tube to end plug (SS 316L) joints was carried out by High

temperature nicrobrazing, Pulsed Nd: YAG laser and GTAW joining processes. A similar work geometry

has been used for all the joining processes. Parameters have been optimized and welds have been

analyzed on the aspects of helium leak detection(HLD), metallographic and micro hardness value. It is

observed that, no observable leak was found during HLD. Micro structures of welds are noticed to have

variation in solidification morphology due to bi-metallic joint area and no cracks were noticed.

Nicrobrazed joints are harder than GTAW and Laser weld joints.

Keywords:- Micro hardness, Stainless steel 316 tube, Stainless steel 316L end plug, High

temperature nicrobrazing, Laser, Gas Tungsten Arc Welding.



Table-1. Chemical composition of materials

used (Wt. %)

Materi

al

C Mn Si P Mo B Cr Ni Fe

Brazin

g

Filler metal

(BNi-

7)

0.03

-

-

10

-

-

14

Balan

ce

-

End plug

(SS 316L)

0.03 - 0.4 0.03 - 0.001

17 13 Balance

Tube

(SS

316)

0.06

7

1.2

7

0.3

7

0.04

1

2.1

0

- 16.9

4

10.04 Balan

ce

3. EXPERIMENTAL PROCEDURES

3.1 High Temperature Nicrobrazing

Fig.2 Arrangement for the development of high-

temperature brazed joints using furnace heating in

an argon gas environment

Sample was placed inside the quartz tube, which in

turn was placed inside the furnace(temperature

range 1200°C) isothermal zone. Argon gas flow

was directed on the component from the height of

around 170 mm inside the quartz tube so that at

brazing temperature (eg. 990°C), oxidation can be

avoided and at the same time brazing alloy which is

in the form of powder should not get disturbed.

Arrangement for the development of high-

temperature brazed joints using furnace heating in

an argon gas environment is shown in Fig-2. A

number of trials were carried out to optimize the

brazing parameters such as peak temperature,

duration (time) at peak temperature, argon flow rate

etc and have been recorded. Parameters recorded

during one of the high-temperature brazing

operation during heating and cooling is given in the

Table-2.

Table.2 Optimised parameters for high temperature

furnace brazing

3.2 Gas Tungsten Arc Welding (GTAW)

Heat input in GTAW does not depend on the filler

material rate. Consequently, the process allows a

precise control of heat addiction and the production

of superior quality welds, with low distortion and

free of spatter. It is less economical than other

consumable electrode arc welding processes, due to

its lower deposition rate, and it is sensitive to windy

environment because of the difficulty in shielding

the weld pool. Besides it shows low tolerance to

contaminants on filler or base metals.

Fig.3 shows the GTA welding equipment during

operation, current has direct influence on weld bead

shape, on welding speed and quality of the weld.

Most GTAW welds employ direct current on

electrode negative (DCEN) (straight polarity)

because it produces higher weld penetration depth

and higher travel speed than on electrode positive

(DCEP) (reverse polarity). Besides, reverse polarity

produces rapid heating and degradation of the

S.

No

Peak

Temperature(deg.cel)

Duration/Time

(min)

Argon gas flow rate

(lpm)

During Heating

1 990 30 10

During Cooling

1 Temperature drop up

to 50

25 10, stopped @ 50

ᴼC



electrode tip, because anode is more heated than

cathode in gas tungsten electric arc [4].

Fig. 3 GTAW during operation

3.2.1 Process parameters

Efficiency of GTAW process is taken as 80% [5]

Shielding gas(argon) flow rate = 10 lpm

Weld current = 40 Amps

Voltage = 8 Volts

Distance = 50.24 mm

Operational time = 50 sec

Traverse speed = 1.0048 mm/sec

Heat input GTAW = 254.77 J/mm

3.3 Pulsed Nd: YAG Laser welding

Fig.4 CNC Laser work stage

Fig.4 shows the solid-state laser of Nd:YAG type,

(average power of 530 W and pulsed power of 10

KW) made of a solid yttrium aluminum garnet rod

doped with neodymium. Excitation of electrons in

neodymium is done with high-power xenon flash

lamps.

3.3.1 Process parameters

If percentage of over lapping factor is more than

70 % , the welds are good. So check this factor by

using our process parameters.

% of over lapping factor (Qf) = �1 − �.��.�� * 100

where,

V = weld speed/traverse speed (mm/sec)

ds = spot diameter (mm)

tf = 1/frequency

tp = pulse duration

Qf = �1 − �∗( ��)�.��(�∗�∗��)� *100

Qf = 78.357 %Now Qf >70 % so the welds are

good.Table-3 shows the process parameters of all

the joining processes used for this application.

Table.3 Optimized Process Parameters of Pulsed

Laser, GTAW and Nicrobrazing Processes

Parameters Pulsed

Laser

GTAW Nicrobrazing

Peak power, KW Pulse duration, ms

Frequency, pps

Pulse energy, J

Mean power, W

Heat Input, J/mm

2.5 8

15

20

300

97.5

--- ---

---

---

---

254.77

---

Arc current, A

Voltage, V

--

--

40

8

---

---

Temperature, °C

Time, min

---

---

---

---

990

30

Defocusing distance,

mm

Spot diameter, mm Electrode diameter, mm

Arc gap, mm

0

0.6

-- --

--

--

2.4 1.5

---

Shielding gas Flow rate, lpm

99.99% Pure Argon

10 10 10

Traverse speed, mm/s 2 1.0048 ---



4.0 RESULTS AND DISCUSSION

4.1 Helium Leak Test

Helium leak detection (HLD) test was used to

detect helium leakage through the high temperature

nicrobrazed joints, GTAW and Laser welds. No

observable leak was found during HLD test at

3.3*10-9

mbar.lit/sec. Fig.5 shows the samples of all

the joining processes.

Fig.5 Samples of all the joining processes

4.2 Metallographic Analysis Samples were cut circumferentially and mould was

prepared. Thereafter, grinding and polishing were

done. Emery sheet of grade 120 for 12 minute and

emery sheet of grade 400 for 3 minute were used

for fine grinding. After grinding and polishing,

etching was carried out on the samples by using

electrolytic etching for 10 sec with oxalic acid as

electrolyte.

(a) Laser

(b) GTAW

(c) Brazing

Fig.6 Micro structures of weld joints at its centre

No cracks have been observed in the joint regions

made by Laser, GTAW and brazing processes.

Fig.6 and fig.7 shows the microstructures at centre

of the weld joints, in Laser we noticed that two

different size grains(fine grains and elongated

grains) were formed due to difference in

solidification. In other two processes we could not

observe any major difference in grain shape. The

aim of metallographic analysis is to find any cracks

are formed in the joint region. We have noticed that

no cracks on the joint regions.

(a) Laser



(b) GTAW

(c) Brazing

Fig.7 Micro structures of weld joints at higher

magnification

4.3 Micro Hardness Test

We have done micro hardness test on joint regions

made by all the three joining processes were

discussed in this paper, test load of 200 gf and

dwell time of 10 seconds. We have noticed the

difference in hardness values of all the three joining

process were used in this analysis. High

temperature nicrobrazing joints have more hardness

value than other two joining(Laser and GTAW)

processes. Fig.8 shows the hardness values obtained

by all the three joining processes.

From the fig.8 we have calculated an average value

of hardness. High temperature nicrobrazing method

gave higher hardness value. Due to this high

hardness value, we can expect the more strength.

Table-4 shows the hardness values of the joining

processes.

Fig.8 Micro hardness values obtained by all the

three joining processes

Table.4 Average values of micro hardness

S.No Joining process Average Micro Hardness

value(HV)

1 GTAW 259

2 Laser 260

3 Brazing 391

5.0 CONCLUSION

• Process parameters have been optimized on

AISI 316 stainless steel tube to end plug (SS

316L) joints by High temperature

nicrobrazing, Pulsed Nd: YAG laser and

GTAW joining processes.

• We have noticed that High temperature

nicrobrazed joints are harder than other two

joining processes.

• Due to this higher hardness value we can

expect that the joint strength may be more in



brazed joints but due to its higher hardness,

ductility of the joint will be reduced, it may

show an effect on joint strength.

Acknowledgement

The authors express their thanks to R. Ramesh,

Metallurgy and Materials Group, IGCAR for

support and encouragement.

REFERENCES

1 M Schwartz Mel , Sikorsky Air craft, 6

(Fundamentals of Brazing, ASM, 1993) 114-125.

2 M. Melvin Schwartz, Sikorsky Air craft, 6

(Introduction to Brazing and Soldering, ASM, 1993)

109-113.

3 HE Pattee, High-Temperature Brazing, Source

book (Brazing and Brazing Technology, ASM 1980).

4 Pires J Norberto, Loureiro Altino and Bolmsjo

Gunnar (Welding Robots, Springer publishers,

2005).

5 Fuerschbach PW and Knorovsky GA, A Study of

Melting Efficiency in Plasma Arc and Gas Tungsten

Arc Welding, Welding Journal 1991, 287s-297s.

[IJET-V1I5P3] Authors :Sadu Venkatesu , R. Saxena , P.K. Chaurasia , R. Ravi kumar , S. Murugan and S. Venugopal

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