Quarterly Publication Rs. 20 APRIL 2019 Weld 18 Bead 1 - IWSiws.org.in/IWS JOURNAL APRIL2019 WELD 18...

Quarterly Publication Rs. 20

APRIL 2019 Weld 18 Bead 1

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AROUND IWS

IWS DAY CELEBRATIONS 2019

INAUGURATION OF STUDENT FORUM AT

RAMCO INSTITUTE OF TECHNOLOGY

KNOWLEDGE SHARING

HENOSIS 19

STRUCTURED COURSE BY IWS, SZ

TECHNICAL PAPERS

EFFECT OF FORGING PRESSURE &

FORGING TIME ON MECHANICAL

PROPERTIES AND MICROSTRUCTURAL

CHARACTERISTICS OF LINEAR FRICTION

WELDED TI-6Al-4V ALLOY JOINTS

POWER BEAM PROCESSING IN THE

MICRO RANGE

THE JOURNAL OF

Regn. No. 41817 / 2002

QUARTERLY PUBLICATION

April 2019 Weld: 18 Bead: 1

PRESIDENT

SHRI S BISWAS

Immediate Past President

SHRI S GOPINATH

Past President

SHRI A V KRISHNAN

Vice Presidents

SHRI A MARUTHAMUTHU SHRI U D RANE SHRI M P JAIN

Hon. Secretary

SHRI N RAJASEKARAN

Hon. Treasurer

SHRI G RAJENDRAN

Members

Dr K Asokkumar Shri R Subburayalu

Mrs. A Santhakumari Dr. T Senthil Kumar

Shri S Rajendran Dr. K Siva Prasad

Dr G Madhusudan Reddy Dr Shashikantha Karinka

Shri Narain Dharmendra Dr V R Krishnan

Prof. Sunil Pandey Dr G Padmanabham

Shri Basu B K Shri Muneesh Narain

Shri Umesh Agarwal Dr T A Daniel Sagaya Raj

Shri Sandeep Mohan Ubhaykar Shri Uma Shanker G

Shri Amit Agarwal Dr T J Prasadarao

Shri Viral Ashok Shah Shri S N Roy

Shri Easwaran R Prof. V Balasubramanian

Shri Tamboli V B Dr M Kamaraj

EDITORIAL BOARD

Shri R SUBBARAYALU – Editor in Charge Dr. G Madhusudhan Reddy Dr. V. Balasubramanian Mrs. A. Santhakumari Dr. T. Senthilkumar

ASSOCIATE EDITORS Shri Praveen Kumar Lakavat Shri R. Arivazhagan

CO-ORDINATORS Shri Sanjay Kadam Shri K Ganesh Kumar Dr. S. Aravindhan

PUBLISHED BY

On Behalf of IWS by

Shri N RAJASEKARAN Hon. Secretary (IWS)

INDIAN WELDING SOCIETY INSTITUTIONS BUILDING, KAILASAPURAM, TIRUCHIRAPPALLI – 620 014

INDIA Websites: www.iws.org.in www.iwsevents.com E mail: [email protected]

http://www.iws.org.in/http://www.iwsevents.com/mailto:[email protected]

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IWS DAY CELEBRATIONS 2019

On the evening of 14th March 2019, the HQ and Southern Zone have jointly celebrated the IWS DAY at

the S K Mazumder Hall, Institutions Building, BHEL Township, Tiruchirappalli. Mr. A. Maruthamuthu,

Vice President (IWS) presided over the function and delivered the IWS day address to the members. He

recalled the successful conduct of IWS 2k18 and SOJOM 2018 by HQ with the support of WZ and by SZ

respectively. Mr. K Ganesh Kumar, Hon. Secretary, IWS, SZ welcomed the gathering. Mr. N Rajasekaran,

Hon. Secretary, IWS recalled the history of IWS and the past accomplishments. Mr. N Parameswaran

conducted the proceedings and proposed the vote of thanks.

AROUND

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IWS STUDENT FORUM AT RAMCO INSTITUTE OF TECHNOLOGY,

RAJAPALAYAM

One more Student Forum of IWS was inaugurated at Ramco Institute of Technology, Rajapalayam, Tamil

Nadu on 3rd January 2019. Mr. A. Maruthamuthu, Chairman (IWS, SZ) & then General Manager (DTG),

Bharat Heavy Electricals Limited, Tiruchirappalli inaugurated the centre in the presence of Mr N

Rajasekaran, Hon. Secretary (IWS) and Mr R Ravibharath, Hon. Treasurer of IWS, SZ. Mr. Maruthmuthu

also presented the ‘IWS welcome kit’ containing the proceedings of the past event to the library of the

college.

In his address, he explained the importance of becoming

the members of Indian Welding Society. He said that

students will find it beneficial to attend workshop,

conferences and technical events organised by Indian

Welding Society Students Forum. Students will get

industrial exposure in advanced welding Technology and

its applications by attending technical talks by industry

experts. Dr. N. Jawahar, Principal, Ramco Institute of

Technology presided over the function. Mr. N. Rajasekaran, and Mr. R. Ravibharath, offered their

felicitations. 76 students and one faculty member were inducted in the forum.

Immediately after the inauguration Mr. N Rajasekaran, delivered a free lecture on "Advanced Welding

Processes for Power Plant Equipments" for the students.

KNOWLEDGE SHARING

ONE DAY TECHNICAL SYMPOSIUM “HENOSIS 19” BY DR. N G P INSTITUTE OF

TECHNOLOGY

The IWS student forum at Dr NGP Institute of Technology

conducted “Henosis ‘19”, a National Level Technical

Symposium, in association with Dr. NGP Institute of

Technology and professional bodies like IEEE, SAE & ISACA

on February 2, 2019.

Seven engineering departments of Dr. N.G.P Institute of

Technology jointly organized the several technical and non-technical events of Henosis ’19. The event

aims to encourage the students to exhibit their talents. Henosis’ 19 provided diversity in the events and

opened up new grounds of exploration and experience for students.

The technical symposium brought together people of varied experiences and provided an opportunity

to everyone to share their thoughts. Mutual participation and high quality deliberations created

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inspiring learning environment resulting into innovative ideas. Today’s industry expects such inputs to

bring home new innovations and inventions.

STRUCTURED COURSES

The Southern Zone conducted its flagship course “Welding

Technology for Fresh Engineers Course (EC 052)” during

11.02.2019 – 17.02.2019. 31 students from various

engineering colleges and industries have attended the

course and got benefited by the heavily subsidized course.

Mr. A. Maruthamuthu,

Chairman, IWS, SZ,

inaugurated the course and distributed the course materials to the

participants.

Mr. N Rajasekaran, Hon. Secretary, IWS offered his felicitations and

shared the genesis of the course. Mr K Ganeshkumar, Hon. Secretary,

SZ welcomed the gathering. Mr. R Ravibharath, Hon. Treasurer, SZ, proposed the vote of thanks.

ON 17th Feb 2019, Mr. N Rajasekaran, Hon.

Secretary (IWS) distributed the certificates to the

participants and delivered the valedictory address.

Mr. Praveen Kumar Lakavat, Course Director (IWS,

SZ) welcomed the gathering. Mr. K E R Chari, EC

Member (IWS, SZ) proposed the vote of thanks.

The participants expressed that they got

benefited from the course and thanked IWS for

the noble initiative.

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EFFECT OF FORGING PRESSURE & FORGING TIME ON MECHANICAL

PROPERTIES AND MICROSTRUCTURAL CHARACTERISTICS OF

LINEAR FRICTION WELDED TI-6Al-4V ALLOY JOINTS *1P. Sivaraj, 2C. Rajarajan, 3V. Balasubramanian, 4Vijay Petley, & 5Shweta Verma

1 ,2 ,3Centre for Materials Joining and Research (CEMAJOR), Department of Manufacturing Engineering Annamalai University, Annamalai Nagar

4,5Gas Turbine Research Establishment (GTRE), DRDO, Bengaluru.

*Email: [email protected]

ABSTRACT

Ti-6Al-4V (also called as Ti64) is frequently used for structural applications in the

aerospace industry due to its excellent strength and light weight. Ti64 can be welded by

almost all the fusion welding processes but resulted in the formation of coarse grained

microstructure in the fusion zone, severe deformation, and high residual stresses. To

overcome these problems, solid state welding processes are now adopted in the

aerospace industries because it avoids total melting of materials and provides finer grain

structures in the nugget region. Among different solid state techniques, linear friction

welding (LFW) is highly suitable to join the blade to disk assembly in the next generation

aero engines. LFW important process parameters are: friction pressure, friction time,

forging pressure, forging time and oscillating frequency. In order to study the effect of

friction pressure and forging pressure, other parameters were kept constant. The forging

pressure was varied from 5 MPa to 15 MPa and the forging time was varied from 2 Sec to

6 Sec. It is found that forging pressure, the relative motion between the mating surfaces

is minimum and it results in poor joint strength.

Keywords: Ti-6Al-4V alloy, Linear Friction Welding, Forging Pressure, Forging Time, Microstructure

Micro hardness, Tensile Properties.

1.0 INTRODUCTION

Ti-6Al-4V [Ti-64] alloy is widely used in aerospace, automobile, nuclear and petrochemical

industries due to its corrosion resistance, high temperature mechanical properties, and low

density [1]. In particular, Ti-64 is used in bladed disk [blisk] assembly in aero engines [2]. Gas

tungsten arc welding (GTAW or TIG) process is widely used for joining titanium alloys, particularly

in sheet forms. High heat input of TIG welding results in greater distortion, and contamination

[3]. Radiant energy welding processes like laser beam (LB) and electron beam (EB) welding

processes are also used for joining titanium alloys but the higher cooling rate possesses problems

like porosity and fusion zone cracking [4]. Solid state welding processes like friction welding,

friction stir welding and diffusion bonding are widely used to join both similar and dissimilar

joints of titanium alloys. Among different solid state welding processes, friction welding offers

many advantages like, elimination of consumables, less welding time, higher joint efficiency etc...

Linear Friction Welding (LFW) is a variant of friction welding process, where the joint between

mailto:[email protected]

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two materials are made by the relative motion and the compressive forces. In LFW, one part is

kept stationary and other part is oscillating linearly. During this process, the frictional heat will

be generated between the surfaces and the plasticized region forms at the interface. After this,

forging force is applied to produce a final joint with a limited thermo mechanically affected zone

(TMAZ) [5].

Abbasi et al. [6] investigated the effect of filler metal on microstructure and mechanical

properties of Ti-6Al-4V joints. The joint fabricated with matching filler exhibited higher tensile

strength than others. The microstructure of the weld metal consists of both acicular and basket

weave morphologies. Kishore Babu et al. [7] studied the effect of current pulsing and post weld

heat treatment on microstructure and mechanical properties of TIG weldments of Ti64. The

current pulsing resulted in refinement of prior β grains which improves both strength and

ductility of the weldments. An increase in ductility and reduction in strength was observed for

the post weld heat treated weldments due to the coarsening of α grains, reduction in defect

density and decomposition of martensite. Balasubramanian et al. [8] investigated the corrosion

behaviour of pulsed gas tungsten arc welded Ti64 joints. The corrosion resistance increased with

increasing pulsing frequency and peak current and then decreased. The finer grains developed in

the fusion zone will be responsible for the increased corrosion resistance. Cao et al. [9] studied

the effect of welding speed on microstructure and mechanical properties of laser welded Ti64

joints. The presence of α' in the fusion zone will increase the hardness by 20 % with respect to

base metal. The microstructure is inhomogeneous across the weld joint and the tensile strength

of the joint is found to be increased with a reduction in ductility.

Romero et al. [10] studied the effect of forging pressure on microstructure and residual stress

development of Ti64 linear friction welds. From his study they concluded that the forging

pressure has strong influence on weld width and thermos-mechanically affected zone (TMAZ).

During welding the temperature developed at the weld region and TMAZ exceeds β transition

temperature. At low forging pressure, the amount of α-Ti is more and it is decreased with

increasing the forging pressure. Increase in forging pressure decreases the residual stresses in

both x and y direction. Li et al. [11] studied the effect of friction time on flash shape and upset of

linear friction welded steel joints. From the study they concluded that the upset length increases

linearly with increasing friction time. The formation of flash is undulating-ribbon structure in the

direction of friction and curly edges in the vertical direction. Effects of processing parameters

were studied by Li et al. [12] through numerical study. At higher oscillating frequency, the

interface temperature increases quickly, and axial shortening occurs at a faster rate. Similar

behaviour is also observed for amplitude and friction pressure.

From the literature review, it is understood that Ti64 alloys were welded by many fusion welding

techniques. However, published information on joining Ti64 alloy by fusion based processes are

very minimum. Moreover, only very few investigators studied on linear friction welding of Ti64

alloy. Hence, the present investigation was carried out to understand the effect of forging

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pressure and friction time on microstructure characteristics and mechanical properties of linear

friction welded Ti64 alloy joints.

2.0 EXPERIMENTAL DETAILS

The rolled plates of Ti64 alloy used in aero engine applications were used in this investigation.

The dimensions of the plates are 60 × 30 × 6 mm (length × width × thickness). The chemical

composition and mechanical properties of Ti64 alloy used in this investigation are presented in

Table 1and 2 respectively. The optical micrograph of Ti64 base metal is shown in Figure1a which

consists of bimodal structure of α and β. The SEM image (Figure 1b) of Ti64 base metal consists

of elongated α grains with intergranular β.

In order to find the effect of forging pressure and forging time, the other welding parameters

such as friction pressure (22 MPa), friction time (40 sec), and oscillation frequency (14 Hz) were

kept constant. The forging pressure and forging time were varied between 5 MPa to 15MPa at an

interval of 5 MPa and 2 sec to 6 sec at an interval of 2 sec respectively. The Table 3 shows welding

parameters used to fabricate the joints. In total 6 joints were made.

Tensile test was performed on defect free joints using a servo hydraulic controlled universal

testing machine at a constant strain rate of 2.4×10-3 s-1. During the test, the load-displacement

curves were recorded using data acquisition system and they are converted as stress-strain

curves. Micro hardness variations across the joints were measured using Vickers’s micro hardness

tester. Hardness was measured at an interval of 0.2 mm in the weld nugget (WN) and thermo-

mechanically affected zone (TMAZ) and an interval of 0.5 mm in heat affected zone (HAZ) and un-

affected base metal (BM). Microstructural features of defect free joints were characterized using

optical microscopy (OM) and scanning electron microscopy (SEM). The microstructural features

were revealed using Kroll's reagent (100 ml H20 + 2 ml HF + 5 ml HNO3).

3.0 RESULTS AND DISCUSSION

3.1 Effect of Forging Pressure on Macrostructure

In Table 4 it shows the effect of forging pressure on macrostructure. At a forging pressure of 10

MPa, it produces sufficient amount of frictional heat at the interface of the weldment which in-

turn plasticize the material. This sufficient heat results in good weld between the mating surfaces.

A uniform flash formation is observed in the joint made using a forging pressure of 10 MPa. The

macrograph reveals defect free joint and the good flash formation. The flash formation is also

uniform on both the sides and the width of the weld nugget (WN) zone is wider than the joint

produced using forging pressure of 10 MPa. When the forging pressure was less than 10 MPa it

produced good flash formation, but the weld nugget zone was minimum and hence, the strength

of the joint was lower compared to the optimized parameter. When the forging pressure was

more than 10 MPa the joint was welded but the joint obtained was having upset (mismatch).

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3.2 Effect of Forging Time on Macrostructure

The macrograph of the linear friction welded joints is depicted in Table 5. The macrograph of the

joint produced using a forging time of 4 sec and forging pressure of 10 MPa shows the defect free

weld. From the fixed end the application forging time gives better impact on sound weld. The

rubbing action against the faying surfaces in linear motion produces sufficient frictional heat to

plasticize the material. This heat results in good weld between the mating surfaces if forging time

is applied for few seconds. The optimized forging time for the joint was 4 sec. When forging time

was less than 4 sec it resulted in poor weld with macro level defect which is shown in Table 4.

When the forging time was above 4 sec it resulted with non-uniform flash formation and the

width of the weld nugget zone was also reduced compared to the optimized condition (4 sec).

From the macrograph observations, it is understood that the joint produced using the forging

time of 4 Sec and forging pressure of 10 MPa yielded a defect free joint with appreciable flash

formation. This is due to the sufficient heat produced as well as forging between the faying

surfaces. For further testing and characterization these defect free joints alone utilized.

3.3 Tensile Properties

The tensile properties of LFW joints such as yield strength (YS), ultimate tensile strength (UTS),

uniform elongation (UE) and total elongation (TE) are shown in Table 6. In each case, three

specimens were tested, and the average values are reported in Table 6. The tensile properties are

slightly lower than that of base metals for both the forging pressure and forging time tensile

strength values. The tensile strength is higher for the forging pressure of 10 MPa. The joint

efficiency is calculated as the ratio between weld joint to base metal.

The tensile specimens are failed slightly away from the Weld Nugget Zone (WNZ) i.e., TMAZ. The

ductility of the weld joints is lower than the base metal. From the table it is understood that

forging pressure is the most influencing welding parameter for obtaining high strength and joint

efficiency.

3.4 Micro hardness Variations across the Joints

The micro hardness variation across the welded joint measured at mid thickness region is shown

in Figure 2. The hardness of the Ti64 base metal is around 340 ± 10 HV. The hardness is increased

to a value of 389±10 HV at the weld nugget zone and it is decreased at the TMAZ region.

The hardness in the heat affected zone (HAZ) was decreased further for both the forging pressure

and forging time. The increased hardness in the WNZ may be attributed to the phase

transformation and refinement of the grains. The combined action of forging time and forging

pressure resulted in elongated coarse grains at the TMAZ region. Hence, the hardness was slightly

decreased at this region. The hardness of the interface between HAZ and TMAZ is lowest when

compared with other regions. This may be due to the phase transformation and high cooling

rates. The joint fabricated using optimized forging time and forging pressure exhibited higher

hardness in the WNZ and away from the weld interface the hardness is decreased.

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From the hardness profile, it is clear that the interface between HAZ-TMAZ regions is found to be

the weakest region across the joint. The hardness profile is also consistent with the tensile

properties since the failure of the joint is at the TMAZ-HAZ interface region. Similarly, forging

pressure is the most influencing welding parameter for obtaining higher hardness in the WNZ

when compared to forging time.

3.5 Fracture Surface Analysis

The SEM fractograph of tensile tested specimens are shown in Figure 3 which indicates the ductile

mode of fracture with variation in dimple size. Both the tensile specimens are failed in the TMAZ

region with marginal variation in ductility. The ductility and the strength are higher for the forging

pressure (10) MPa which is evident from the fracture surface. It consists of finer dimples which

are shown in Figure 3b. The joint fabricated using forging time (4 sec) shows marginally elongated

dimples which are shown in Figure 3a. It indicates the lower strength and hardness of the joint

which is evident from the tensile and hardness results.

3.6 Microstructural Features of LFW Joint

The microstructural features of the joint produced with the optimized parameters of forging

pressure and forging time is shown in Figure 4. Generally, the microstructural zones in LFW joint

is classified as weld nugget zone (WNZ), thermo-mechanically affected zone (TMAZ), heat

affected zone (HAZ), and un-affected base metal (BM). The microstructural features of two

different parameters were compared for better understanding. The microstructure in the WNZ

(Figure 4a and 4b) is entirely different from the base metal. The bimodal microstructure of alpha

and beta grains in the base metal were totally transformed into widmanstatten (basket weave)

structure. The width of the WNZ is wider for the forging pressure than the forging time. During

LFW, the interface temperature exceeds to a value of 995 °C. This temperature will transform the

bimodal alpha and beta grains into the single-phase beta field. The higher cooling rate results in

diffusion less transformation of beta grains into the martensitic (widmanstatten) structure. It is

also observed that, the hardness of this region (Figure 4) is higher than the base metal.

The microstructure of the TMAZ is shown in Figure 4 (c-d). This region is very narrow compared

to the WNZ and it is highly deformed due to the combined action of forging pressure and forging

time. The temperature at this is region is well below to the beta transition temperature (below

995 °C). Here, there is no phase transformation at this region. The original bimodal alpha and

beta grains is reoriented during linear friction welding. The microstructure in the HAZ is almost

same as the TMAZ region. In HAZ, the grains are softened due to the convectional heat transfer.

The grain sizes are almost same for both the parameters. This inhomogeneous microstructure is

consistent with the hardness profiles and tensile properties. The failure of the tensile specimens

is at the TMAZ region which due to the presence of elongated alpha and beta grains with

reoriented features.

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CONCLUSIONS

In the present investigation, the effect of forging pressure and forging time on tensile properties

and microstructural characteristics of linear friction welded Ti64 alloy joints was studied. The

important conclusions are as follows:

The joint fabricated using forging pressure of 10 MPa and forging time of 4 sec resulted in

good flash formation as well as wider weld nugget zone which yielded defect free joints.

The maximum joint efficiency of 98 % was achieved in forging pressure.

The joints fabricated using forging pressure of 10 MPa exhibited superior tensile properties

due to the presence of wider weld nugget zone and hence, forging pressure was found to

be the most influencing welding parameter for the fabrication.

The lowest hardness value is recorded at the interface between TMAZ-HAZ in both the

joints due to the presence of elongated coarse grains.

ACKNOWLEDGEMENT

The authors are thankful to the Gas Turbine Research Establishment (GTRE), DRDO, Bengaluru

for providing financial assistance through Contract Acquisition Research Support (CARS) scheme

(No. GTRE/MMG/BMR1/1023/16/CARS/A/16) to carry out this investigation. The authors are

thankful to the Director, GTRE, Bengaluru for providing Ti64 alloy materials to carry out this

investigation.

REFERENCES

[1] X.-L. Gao, L.-J. Zhang, J. Liu, and J.-X. Zhang, A Comparative Study of Pulsed Nd:YAG Laser Welding and TIG Welding of Thin Ti6Al4V Titanium Alloy Plate, Mater. Sci. Eng. A, Elsevier, 2013, 559, p 14–21, doi:10.1016/j.msea.2012.06.016.

[2] Bhamji, M. Preuss, P.L. Threadgill, and A.C. Addison, Solid State Joining of Metals by Linear Friction Welding: A Literature Review, Mater. Sci. Technol., 2011, 27(1), p 2–12, doi:10.1179/026708310X520510.

[3] Y. Guo, M.M. Attallah, Y. Chiu, H. Li, S. Bray, and P. Bowen, Spatial Variation of Microtexture in Linear Friction Welded Ti-6Al-4V, Mater. Charact., Elsevier Inc, 2017, 127, p 342–347, doi:10.1016/j.matchar.2017.03.019

[4] Fall, M. Jahazi, A.R. Khodabandeh, and M.H. Fesharaki, Erratum to: Effect of Process Parameters on Microstructure and Mechanical Properties of Friction Stir-Welded Ti–6Al–4V Joints (The International Journal of Advanced Manufacturing Technology, (2017), 91, 5-8, (2919-2931), 10.1007/s00170-016-9527-Y), Int. J. Adv. Manuf. Technol., The International Journal of Advanced Manufacturing Technology, 2017, 91(5–8), p 2933, doi:10.1007/s00170-017-0519-3.

[5] P. Wanjara and M. Jahazi, Linear Friction Welding of Ti-6Al-4V : Processing, Microstructure , and Mechanical-Property Inter-Relationships, 2005, 36(August).

[6] Abbasi, K., Beidokhti, B., & Sajjadi, S. A. (2017). Microstructure and mechanical properties of Ti-6Al-4V welds using α, near-α and α+β filler alloys. Materials Science and Engineering: A, 702, 272–278. https://doi.org/10.1016/j.msea.2017.07.027

[7] Kishore Babu, N., Ganesh Sundara Raman, S., Mythili, R., & Saroja, S. (2007). Correlation of microstructure with mechanical properties of TIG weldments of Ti-6Al-4V made with and without current pulsing. Materials Characterization, 58(7), 581–587. doi:10.1016/j.matchar.2006.07.001

[8] Balasubramanian, M., Jayabalan, V., & Balasubramanian, V. (2008). Effect of pulsed gas tungsten arc welding on corrosion behavior of Ti–6Al–4V titanium alloy. Materials & Design, 29(7), 1359–1363. doi:10.1016/j.matdes.2007.06.009

[9] Cao, X., & Jahazi, M. (2009). Effect of welding speed on butt joint quality of Ti-6Al-4V alloy welded using a high-power Nd:YAG laser. Optics and Lasers in Engineering, 47(11), 1231–1241. doi:10.1016/j.optlaseng.2009.05.010

https://doi.org/10.1016/j.msea.2017.07.027

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[10] Romero, J., Attallah, M. M., Preuss, M., Karadge, M., & Bray, S. E. (2009). Effect of the forging pressure on the microstructure and residual stress development in Ti-6Al-4V linear friction welds. Acta Materialia, 57(18), 5582–5592. doi:10.1016/j.actamat.2009.07.055

[11] Li, W. Y., Ma, T. J., Yang, S. Q., Xu, Q. Z., Zhang, Y., Li, J. L., & Liao, H. L. (2008). Effect of friction time on flash shape and axial shortening of linear friction welded 45 steel. Materials Letters, 62(2), 293–296. doi:10.1016/j.matlet.2007.05.037

[12] Li, W.-Y. W.-Y., Ma, T., & Li, J. (2010). Numerical simulation of linear friction welding of titanium alloy: Effects of processing parameters. Materials & Design, 31(3), 1497–1507. doi:10.1016/j.matdes.2009.08.023

Table 1 Chemical composition (wt%) of Ti64 base metal

Elements (wt %) Al V Fe O C N H Ti

Ti-6Al-4V 6 4 0.19 0.15 0.06 0.04 0.01 Bal.

Table 2 Mechanical properties of Ti64 base metal

0.2%Yield Strength (MPa)

Tensile Strength (MPa)

Elongation in 50 mm gauge length (%)

Reduction in Cross Sectional Area (%)

Hardness (HRc)

980 1030 12 24 33

Table 3 Welding Parameters used to fabricate the joints

Joint Number

Forging Pressure (MPa)

Forging Time (sec)

Friction Pressure (MPa)

Friction Time (sec)

Oscillating Frequency (Hz)

1 5 4 22 15 14

2 10 4 22 15 14

3 15 4 22 15 14

4 10 2 22 15 14

5 10 4 22 15 14

6 10 6 22 15 14

Table 4 The Effect of Forging Pressure

Joint Forging Pressure

(MPa) Macrograph Observation

1 5

Welded with good flash formation on both sides

2 10

Welded with good flash formation and weld beed also good

3 15

The joint was welded but not straight and upset happed due to high

forging pressure

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Table 5 The Effect of Forging Time

Joint Forging Time (sec) Macrograph Observation

4 2

Welded with macro level defect

5 4

Welded with good flash formation and weld beed also good

6 6

Welded with non-uniform flash formation

Table 6 Tensile properties of LFW joints

Joint Number

0.2% Yield strength (MPa)

Tensile strength (MPa)

Total Elongation (%)

Joint efficiency (%)

2 926 1011 8.4 98

5 900 975 7.1 94

(a) Optical micrograph of base metal (b) SEM image of base metal

Fig 1 Micrographs of Ti64 - base metal

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Fig 2 Micro hardness variation across the joint

Joint No. 5 Joint No. 2

Fig 3 Fracture surfaces of tensile specimens

(a) WNZ (d)WNZ

(b) TMAZ (e) TMAZ

(c) HAZ (f) HAZ

Fig 4 Microstructural features of LFW joints (a), (b), (c) - Joint Number 5 (d), (e), (f) - Joint Number 2

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POWER BEAM PROCESSING IN THE MICRO RANGE M. Merkel, M. Escher, Ch. Otten & St. Jakobs*

Focus GmbH, Germany

*ISF - Welding Institute, Germany

ABSTRACT

Electron beam welding in the micro range is an under estimated joining process in the industry.

Nowadays laser beam welding in vacuum is an upcoming technology. It is a mandatory measure to

investigate in this technologies for the micro processing.

The aim of this paper is to demonstrate the advantages of electron and laser beam welding in

vacuum for micro processing technologies.

To address the special requirements of micro joining tasks for an electron beam welding system a

number of technical modifications are required. The tungsten filament cathode is replaced by a LaB6

single crystal for smaller spot profiles and higher power densities. A fast beam deflection system is

integrated for a higher precision in beam motion by time and position. A high voltage power supply

is integrated enabling fast power regulation in the ms range. Fast pulsing with pulse lengths down

to 1 µs and stable beam currents down to the 10 µA are essential for welding applications joining

very thin micro wires or sheets.

Recently a new laser has been integrated into a vacuum micro processing welding machine (LaVa)

used for similar applications. A short survey and outlook will be given about this very new technology

and its first achievements.

KEY WORDS: Electron Beam Welding, EB Welding, Laser Welding, Laser in Vacuum, Micro Welding,

Micro Structuring, Micro Drilling

1.0 INTRODUCTION

The miniaturization in various high tech industries requires joining methods which can process in

the range of a few microns (Zhou, 2008). Beam joining methods are increasingly gaining in

importance in the Micro System Technology (MST). The Laser is already well established as tool

for micro joining and surface modification. Welding in vacuum reduces the ambient pressure in

the key hole and avoids the plasma plume generated by the ionized gas. These effects stabilize

the welding process drastically known from deep penetration electron beam welds. First

experiments using fibre or disc laser beams for the welding in vacuum demonstrate that similar

advantages can be observed (Reisgen P).

Transforming the micro process technology into vacuum, a row of applications are successfully

performed by the electron beam (Otten). This expands the expectations in quality for welding

and surface modification in the micro range. (Smolka, Gillner, Bosse, & Lützeler, 2004). The

advantage of vacuum and the ability to weld almost all electrically conductive materials, the high

reliability and efficiency and the possibility to focus the beam precisely to a few microns makes

this technique particularly interesting for processing in the micro range.

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Another process related uniqueness is the manipulation in the kHz range due to an almost inertia

free control of the beam with electromagnetic coils. This allows for a high accurate positioning

on the work piece at synchronous short processing times (Knorovsky, Dorfmüller, Dilthey, &

Woeste, 2008). Continues approaches expand the field of successful applications for electron-

and laser beam in vacuum for micro processing industry.

2.0 SYSTEM ENGINEERING

All experiments were done with a FOCUS micro electron beam welder (FOCUS GmbH, 2015). This

system is specially designed to fulfil the requirements for processing in the micro range. The

installation of a fast beam deflection system including the coil and amplifiers with up to 200 kHz

(FOCUS GmbH, 2015) and the redesign of the triode system with a novel filament type as cathode

frame the fundament. For that a LaB6 single crystal with a diameter of 300 µm is used. The main

advantage is a constant beam characteristic and a significantly increased power density over the

whole lifetime of up to 1000 h. The problem of the partial evaporation (Steffens, Sievers, &

Buchmann, 1990) is, due to a pressure of a low 10-6 mbar, minimized.

For laser beam welds the FOCUS micro electron beam welder is equipped with a 600 W single

mode fibre laser. The electron beam column at the top of the vacuum chamber including beam

generation and electron optical System, is exchanged by a Precitec YW52 optics and a 1-D

scanner. For the irradiation of the laser power beam in to the vacuum chamber a specialized

window is required. The system also includes a well - designed vapour shielding device to avoid

metal dust on this window. Refer Figure 01.

3.0 EXAMPLES

3.1 Micro Welding

The first example is a micro electron beam weld to join two 100 µm thick sheets together, Figure

02. The application of this is a hermetically sealed battery housing for electric cars. The material

316L (X2 Cr Ni Mo 17-12-2) is welded with 84 W beam power, 90 mm / s welding speed, a circular

oscillation of 50 µm and free root forming. In Figure 02a, the surface of the sheet is shown. The

weld has a uniform flanking and a constant width of 180 µm. The macro section allows an

examination of the weld appearance (see Figure 02 b). In all analysed welds neither pores nor

cracks can be detected. The fusion line distinguished the steep course from the surface to the

root. A heat affected zone can, due to the precise heat input, not be seen. Though this weld is

done by deep penetration welding with keyhole, the shape reminds more like a heat conductive

weld, which can be explained by the low heat capacity of the parts in the micro range.

3.2 Medical (Electron Beam)

The medical sector demands the highest requirements on the reliability of the products. The

electron beam features advantages in the contactless processing under high vacuum condition

and the material independent energy absorption. The precise focusing is especially needed during

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the welding of devices in the micro-range. Figure 03a, shows a micro electron beam welded

Nitinol (intermetallic phase of NiTi) stent for the air tube. The 200 µm thick wires were welded at

their endpoints with a lap joint. An important fact is the in-situ quality control, due to the high-

resolution SEM mode of the micro EB welding machine. A cross-section of a joint imaged with a

SEM is shown in Figure 03b, except of a few micro cavities a crack free and very homogeneous

microstructure is demonstrated. The good strength coupled with the excellent biocompatibility

has made Nitinol an attractive candidate for medical device applications (Khan & Zhou, 2010).

Some difficulties associated with the mechanical properties after laser welding have been

reported in (Falvo, Furgiuele, & Maletta, 2005) and demonstrate the need of further research

regarding the joining process. Scientific results about electron beam are rare or outdated

(Horikawa, Ueki, & Shiroyama, 1994). The change in the microstructure after welding is particular

important and should be kept as low as possible. In Figure 03c & 03d are two cross section of a

Ni-Ti shape memory alloy demonstrated, c) is welded with the LaB6 cathode and d) with the

wolfram hairpin cathode. Both welds are free of any defects like cracks or pores. The beam power

was incrementally increased with a constant welding speed of 50 mm / s, until a full penetration

is reached. With the wolfram filament the beam power has to be increased from 150 W to 210 W.

The result is a stronger grain growth in the weld and an increase in the width of the HAZ.

3.3 Sensor and Battery Housings (Laser and Electron Beam)

The increasing interest in aluminium alloys can be explained by its special properties and their

importance for light-weight design (Dilthey & Stein, 2006). Besides the application in body

construction, where aluminium is used due to its high strength – to - weight ratio, it is also used

for battery and sensor housing (Hailat, Mian, Chaudhury, Newaz, Patwa, & Herfurth, 2012).

Electron beam technology is particularly interesting for welding aluminium alloys since it provides

high levels of joint efficiency (Tosto, Nenci, & Hu, 1996), (Chen & Huang, 1999) and the absorption

is process related material independent (Schultz, 2000).

From the metallurgical point of view, beam welding of aluminium alloys leads through the high

affinity to oxygen to pores (Gellert, 1998). Welding those materials in vacuum consequently lead

to a process with a strong reduced amount of pores in number and size. Due to the high

solidification range this welding process is sensitive to hot cracks (Gref, 2005). These cracks which

occur in the weld and the HAZ during solidification strongly depend on the used alloy and the

process parameters.

Figure 04 shows examples of sensor housings welded by electron beam and laser beam. Both

were tested via helium leakage test satisfactory to leakage rates of 10-9 mbar l / s. In the full

penetration connection welds, the existence of imperfections, like pores or hot cracks cannot be

detected. Due to the low heat impact of power beam welds the sensor manufacturing can be

improved drastically. If the temperature stays lower than 70 °C during the entire welding process,

sensors can be welded completely assembled even with electronic devices installed inside. The

low heat impact prevents plastic and electronic parts from destruction.

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A reasonable explanation for the crack-free welds is in addition to the high absorption and the

low capacity of heat transmission. The weld is facing the vacuum atmosphere from its upper

surface and the root side. Due to the vacuum condition the reduced heat conduction cannot be

balanced by convective flow of heat which leads to a decreasing cooling rate with extended

degassing time and increased diffusive replacement possibilities. The slower cooling is especially

important for the high crack susceptibility of alloys with multi constitute.

3.4 Vacuum Feed Through (Laser and Electron Beam)

Another application for best sealed and low heat impact requirements are high vacuum feed

throughs for all kind of media, mostly electric power and signals. It is a challenge to seal a

compound of different materials by welding into a stainless steel flange. In certain cases the

leakage rate has to achieve values better than 10-11 mbar l / s. The shown examples are a

demonstration of excellent welds by laser beam or even electron beam of an X5 CrNi Mo17-12-2

pipe with 3 mm wall thickness and a diameter of 25 mm into a stainless steel flange. Refer Figure

05.

3.5 Drilling (Electron Beam)

It is well known that the electron beam is an efficient method for precise and reproducible

drillings in technical work pieces (Leitz, Koch, Otto, Maaz, Löwer, & Schmidt, 2012). The minimum

bore diameter is thereby mainly influenced by the beam profile. The major energy absorption of

the pulsed beam is compared to laser drilling, where the penetration depth of the photons is in

the nanometer range, deeper in the bulk of the work piece achieving a few microns. The FOCUS

MEBW-60 comes with a controlled mode, where it is possible to adjust the pulse form, and a fast

mode, where the control electrode switches between two levels. Figure 06 shows a micro

electron beam drilled 100 µm thick molybdenum apertures.

3.6 Surface Structuring (Electron Beam)

The surface modification of materials is important for many applications (Tavakoli, Buxton, Jones,

& Dance, 2007). One method is a, patented by TWI (Dance, 2002), texturing technique called Surfi-

Sculpt. In that process the electron beam is deflected rapidly over the surface of the material and

displaces material in a highly controlled manner (Reisgen, Olschok, Otten, Panfil, & Fischer, 2012).

Figure 07a, shows a textured stainless steel sheet where 10 x 6 structures were produced at the

same time with multiple beam technique. Therefore a tailored process management is needed

to avoid distortion. Theses specimens were used for steel - plastic dissimilar joints. For the second

exampleTiAl6V4 disks with a diameter of 10 mm were used. The micro structuring was applied

with the goal of a better ingrowths behaviour of implants in the human body (Neuss, et al., 2015).

The distance between the structures is 40 µm and the height is 20 µm. The accuracy in which the

process can be done is in the range of a few microns.

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CONCLUSION

i. The electron beam is a multifaceted tool for material processing in the micro range. There

are applications in many sectors as well as in different processes. The main advantages are

the material independent extremely high absorption, the vacuum conditions, keeping the

work pieces clean and non-oxidized, and the extremely fast, precise and reproducible beam

deflection. The process related high current density and beam quality can be improved by

the use of a LaB6 single crystal as cathode. Due to the precise control abilities, in

combination with the fine beam, processes like micro drilling and surface texturing pushes

the technology into new dimensions.

ii. Exchanging the electron beam column of the welding chamber into a laser beam optic fed

by a single mode fibre laser demonstrates also highest levels in welding quality for the

micro processing. The key factor for success is the ambient low pressure in the evacuated

welding zone.

iii. It is a question of the required flexibility and demands in beam processing or monitoring

that decides about the choice of the best power beam tool.

REFERENCES

1. N. Zhou, Micro joining and Nano joining, Cambridge, England: Wood head Publishing Ltd, 2008.

2. M. Mücke, U. Reisgen, S. Olschok, S. Jakobs, "Welding with Laser in Vacuum: Test results from Automotive

Components", Proceedings SMWC XVI, Livoni Michigan, USA, Oct 2014

3. C. Otten, M. Escher, M. Christ, I. Balz, S. Krasnorutskyi, "Electron beam Processing in the micro range",

Proceedings of 3rd IEBW Conference, Chicago, USA, Nov. 2015

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of beam welding methods in the micro-system technology," Microsystem Technologies, vol. 10, pp. 187-192,

2004.

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Nanojoining, Cambridge, England, Woodhead Publishing Ltd., 2008, pp. 419-472.

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e-welding.de/resources/Sectors/MEBWBroschuere2014.pdf.

7. FOCUS GmbH, "www.focus-gmbh.com," 30 September 2015. [Online]. Available: http://www.focus-

gmbh.com/resources/Electronics/HDCA40_Flyer-german.pdf.

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Materialwissenschaft und Werkstofftechnik, vol. 21, pp. 454-471, 1990.

9. M. I. Khan and Y. Zhou, "Effects of local phase conversion on the tensile loading of pulsed Nd: YAG laser

processed Nitinol," Material Science and Engineering A, vol. 527, pp. 6235-6238, 2010

10. Falvo, F. M. Furgiuele and C. Maletta, "Laser welding of a NiTi alloy: Mechanical and shape memory

behaviour," Materials Science and Engineering A, vol. 412, pp. 235-240, 2005.

11. H. Horikawa, T. Ueki and K. Shiroyama, "Superelastic performance of Ni-Ti thin tubes," in Proceedings of SMST,

Pacific Grove, USA, 1994.

12. U. Dilthey and L. Stein, "Multimaterial car body design: challenge for welding and joining," Science and

Technology of Welding and Joining, vol. 11, no. 2, pp. 135-142, 2006.

http://www.focus-e-welding.de/resources/Sectors/MEBWBroschuere2014.pdfhttp://www.focus-e-welding.de/resources/Sectors/MEBWBroschuere2014.pdfhttp://www.focus-gmbh.com/resources/Electronics/HDCA40_Flyer-german.pdfhttp://www.focus-gmbh.com/resources/Electronics/HDCA40_Flyer-german.pdf

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13. M. Hailat, A. Mian, Z. Chaudhury, G. Newaz, R. Patwa and H. Herfurth, "Laser micro-welding of aluminium

and copper with and without tin foil alloy," Microsystem Technologies, vol. 18, pp. 103-112, 2012.

14. S. Tosto, F. Nenci and J. Hu, "Microstructure and properties of electron beam welded and post-welded 2219

aluminium alloy," Material Science and Technology, vol. 12, no. 4, pp. 323-328, 1996.

15. S. C. Chen and J. C. Huang, "Influence of welding parameters on microstructures and mechanical properties of

electron beam welded aluminium–lithium plates," Material Science and Technology, vol. 15, no. 8, pp. 965-

978 , 1999.

16. H. Schultz, Elektronenstrahlschweißen, Düsseldorf: DVS-Verlag, 2000.

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1998.

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Verlag GmbH, 2005.

19. C. Otten, U. Reisgen, M. Christ, T. Unger and M. Schmachtenberg, "Electron beam welding of AW-2024

aluminum for hermetically sealed sensor housing," in 68th IIW Annual Assembly and International Conference,

Helsinki, Finnland, 2015.

20. K.-. H. Leitz, H. Koch, A. Otto, A. Maaz, T. Löwer and M. Schmidt, "Numerical Simulation of Drilling with Pulsed

Beams," Physics Prcedia, vol. 39, pp. 881-892, 2012.

21. M. Tavakoli, A. Buxton, I. Jones and B. Dance, "The use of power beams in surface modification," Medical

Device Technology, vol. 18, no. 1, pp. 6-12, 2007.

22. B. Dance, "Modulated Surface Modification". International Patent WO 2002/094497 A3, 2002.

23. U. Reisgen, S. Olschok, C. Otten, C. Panfil and H. Fischer, "Electron beam structuration of titanium materials

for medical applications: potential for improved ingrowth behavior," in DVS-Berichte Band 285: International

Electron Beam Welding Conference, 2nd IEBW Conference, Aachen, 2012.

24. S. Neuss, C. Panfil, D. Campos, M. Weber, C. Otten, U. Reisgen and H. Fischer, "Adhesion of human

mesenchymal stem cells can be controlled by electron beam-microstructured titanium alloy surfaces during

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Figure 01 Micro processing system. Usable for any kind of power beam processing in the micro range under vacuum

Figure 02 Micro electron beam weld of 100 µm thick stainless steel foils

a) b)

100 µm

weld

Fusion

line

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Figure 03 Electron beam welding of Nitinol: a) with Lab6 and b) with tungsten filament

Figure 04 Example of sensor welded by electron- and laser beam showing highest welding standards

a) b)

c) d)

500 µm

200 µm 200 µm

weld weldHAZ

HAZ

weld

wire

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Figure 05 Example of a high vacuum electric feed through welded by electron- and laser beam showing highest welding standards

Figure 06 Micro EB-drilling of a 100 µm thick molybdenum aperture

Figure 07 Electron beam structuring: a) on a stainless steel sheet as perpetration for steel-plastic joints; b) on titanium grade 5 plates for a better acceptance in the human body

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