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Issue 169 November/December 2010

Diary events

January 2011

Seminar

Working with composites

Thu 20

Great Abington

February 2011

Technology disseminationseminar

High productivity welding

using variable polarity

submerged arc welding

Wed 9

Middlesbrough

March 2011

Seminar

Linear friction stir welding

Thu 17

Great Abington

Joint Technical Group meetingOffshore Oil and Gas and

Polymers

tbc

Aberdeen

April 2011

Conference

Association of Welding,

Fabrication, Training and

Education

Fri 1Great Abington

May 2011

Conference

The Welding & Joining Society

Wed 18 – Thu 19

Great Abington

Workshops and seminars

are recognised

Continuous Professional

Development events

T h e m a g a z i n e o f T W I

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continued on p 2

Extreme environment materials are

becoming increasingly important in

a number of strategically vital areas.

Ultra-high temperature ceramics (UHTCs),

for example, have been identified as

having an important role to play in nuclear

power generation and radioactive waste

storage. Hypersonic aviation, where

scramjet intake and re-entry vehicle leading

edge temperatures exceed 2000°C, is

another important application area.

However, determining the performance of

UHTCs at such temperatures is challenging

and costly owing to the limited availability

and complex nature of appropriate test

facilities. Consequently, ready access to

more affordable techniques for evaluating

the properties of UHTCs, and other

extreme environment materials, is desirable.

TWI is currently working with Imperial

College London, Loughborough University

and DSTL to develop the collimated laser

beam (CLB) test; a rapid, cost effective

means of assessing the oxidation resistance

of UHTCs, such as HfB2, at temperatures in

excess of 2500°C.

Initially developed by Steve Westgate

(TWI), the CLB test uses a collimated(parallel sided) laser beam. Using a high

brightness ytterbium (Yb) fibre laser beam,

only 5mm in diameter, enables UHTC

samples to be completely bathed in high

heat flux laser light, ie up to

44MW/m2, enabling testing to temperatures

approaching at least 4000°C.

Turning up the heat:

Laser ablation of ultra-high

temperature ceramics

(a) HfB2 specimen, sat on carbon block, prior to and (b) During collimated laser beam (CLB) testing at 44MW/m2 ,

(c) Pyrometer output during CLB testing of HfB2 , and examples of the surface appearance of (d) HfB2 and

(e) HfB2 + 20%SiC UHTC 5mm diameter specimens after CLB testing.

a

b

d

e

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 500 1000 1500 2000 2500 3000 3500 4000

Datapoint number

T e m p e r a t u r e C e l s i u s

Sample sent to 2nd power level

Sample held, 1st power level

Beam on, sample heating

Beam off, sample cooling

c

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November/December 2010

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Aliaxis R&D - SASFrancePlastic pipes and fittingproduction, electrofusion joining

Cambridge ElectronBeamUK Electron beam welding

Cummins Re-ConUSARe-manufacture of engines and components

DBK TechnithermLimitedUK Design and manufactureof heating and coolingsolutions

Hexadex LimitedUK Engineering andmanufacturing

Inspirit Energy LimitedUK Development of microcombined heat andpower (mCHP) appliance

Miller Electric/HobartUSAManufacturer of weldingequipment and products

Philips LightLabsThe NetherlandsLighting

Semblant LtdUK Plasma deposition

SogedecFrancePower plantdecommissioning

TEI Tusas EngineIndustries IncTurkey Aero engine assembly and overhaul

New Membersof TWI

TWI is pleased to welcome the

following as Industrial Members

continued from p.1

Another key feature of the CLB test is

its flexibility. Over twenty specimens can

be evaluated in a day and the heat flux/

duration of each test can be adjusted easily

to simulate a range of environments. Thebeam can be released for one second or,

potentially, an hour and the heat flux within

that beam is controllable to within a few

watts.

Microstructural changes in UHTC specimens

(determined by post-test microstructural

characterisation) along with in-test

pyrometry (under development at TWI)

can then be used to infer the maximum

temperatures reached during testing.(Figure c).

The depth to which UHTC specimens are

oxidised during CLB testing is measured

during subsequent microstructural

characterisation. However, an immediate

qualitative assessment of their oxidationresistance can usually be obtained by post-

test visual inspection (Figures d-e).

In ongoing work, the CLB test facilities

at TWI are being modified to include

the option of introducing active flows of

different gases across the surface of UHTC

specimens during testing to better simulate

anticipated service conditions.

If you are interested in the use of lasers for

the high temperature testing of materials,either for this or other applications, please

contact [email protected]

TWI held its third Technology Awareness

Day on Thursday, 14 October 2010. We

were very pleased to welcome

Professor John Irven, the chairman of TWI’s

Research Board, as our keynote speaker.

For the first time the event was broadcast

live and more than 60 attendees from over

30 member companies took advantage

of the offer of not having to travel and to

benefit from the day by attending online.

We were particularly delighted that some

members even organised a meeting room

at their end and got a group of colleagues

together to watch and listen to the

presentations.

Corrosion and structural integrity

management have been an integral part

of TWI for more than 60 years and TWI

has established a world class reputation

for supplying high calibre services to

clients across all industry sectors. The

morning session focused on corrosion

management and mitigation, the afternoon

on life extension. Presentations and the full

recording of the day are available on our website (for members only):

www.twi.co.uk/content/e141010-2.html

TWI Information Services Stand

TWI Technology Awareness Day 2010:Materials selection and failure avoidance

Professor John Irven, TWI Research Board Chairman

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3

During 2010 TWI has continuedits major investment in high power

laser materials processing equipment.

Four state-of-the-art Yb-fibre lasers

are now operational at TWI in

Cambridge, to enhance the portfolio

of laser processing services offered to

Industrial Members. With a number of

new processing heads now availableat TWI, these Yb-fibre lasers are

suited for a diverse range of welding,

cutting and surfacing applications. The

investment reflects the growing take

up of Yb-fibre laser technology and

the increasing adoption of laser-based

materials processing solutions in many

industry sectors.

The four continuous-wave Yb-fibre

lasers, which have maximum ratedoutput powers of 5kW, 1kW, 200W

and 20W, are typical of the range of

solid-state lasers now being adopted

by industry. Advantages of adopting

fibre or disc laser technology include:

high wall plug efficiency, excellent

beam quality, fibre optic delivery

(allowing easy robotic automation),

small footprint and long service

intervals. The range of output powers

and focused beam properties allowa wide range of materials to be

processed.

For welding applications, the 5kWYb-fibre laser is capable of at least

8mm penetration depth in most

metallic materials and it is possible

to increase joint-gap tolerance using

wire feed, oscillation of the laser beam

and/or a hybrid laser arc process.

Furthermore, Industrial Members now

have access to a laser camera

vision system which allows seam

tracking, adaptive control and

even post-weld inspection of bead geometries. At the other

thickness extreme, metallic foils

of total thickness <500µm can

be joined at welding speeds of

~500mm/s using the 200W

Yb-fibre laser.

The 5 and 1kW lasers are also

ideally suited for high quality

cutting of sheet metal up to

3mm in thickness, with work inprogress to increase this thickness.

Compared with traditional CO2 laser

cutting, a 300% increase in cutting

speed can be achieved using Yb-fibre

lasers. This enhanced process speed,

combined with the increased wall

plug efficiency, enables large cost

savings. Where high cut quality is not

a requirement, cut depths of up to

50mm have already been achieved

with the new Yb-fibre lasers.

Robotic manipulation equipment

is on hand both for high precision

applications and workpieces up to 5m

in length. In addition, a 3D scanning

head is now available for remote

welding, sublimation cutting, marking

and laser Surfi-Sculpt® applicationswith the 1kW laser.

The 20W Yb-fibre laser is coupled to

a fast 2D scanning head, scanning over

a precision 3D displacement stage. This

laser-optic combination is suitable for

micro-marking, scribing, Clearweld®

operations on plastics and thin film

ablation.

Several successful projects have

already been carried out using thenew equipment. These include

concrete scabbling, pipe cutting,

hybrid laser arc welding of steel,

stainless steel and aluminium

alloy, welding of metallic foil, high

quality welding of titanium alloy,

transmission joining of plastic, and

patterning of nano-material coatings.

To discuss the suitability of this

equipment for meeting your business needs please contact

[email protected] .

New laser materials processing

equipment at TWI

Hybrid laser arc set-up with an adaptive control vision

Laser welding with a 200W Yb-bre laser

Single sided tube-in-tube cutting with a 5kW

Yb-bre laser

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Tech nol ogy Tran sfe r

Titanium is a reactive metal; it willburn in pure oxygen at 600OC and innitrogen at around 800OC. Oxygenand nitrogen will also diffuse into titanium at temperatures above400OC raising the tensile strength butembrittling the metal. In the form of a powder or metal shavings titaniumalso constitutes a fire hazard.

Despite this reactivity titanium is usedextensively in chemical processing,offshore and aerospace applications.This is due to:

• The tenacious protective oxidefilm that forms, giving the alloysvery good corrosion resistance,particularly in chloride containingenvironments.

• No loss of toughness at

temperatures down to -196OC• Good creep and oxidation.

resistance at temperatures up toalmost 600OC.

• Similar strength to steel but atapproximately half the weight.

Because of the affinity of titaniumand its alloys for oxygen, nitrogenand hydrogen and the subsequentembrittlement, fluxed weldingprocesses are not recommendedalthough they have been used,primarily in the former USSR. Arcwelding is therefore restricted to thegas shielded processes (TIG, MIGand plasma-TIG) although power beams, the solid phase processes andresistance welding are also used.

Titanium is allotropic; it has twodifferent crystallographic formsdepending on the temperature andchemical composition. Below 880OCit forms the hexagonal close packedalpha phase, above 880OC it exists asbody centred cubic beta phase.

A range of elementsmay be used

to improve themechanical properties,

some stabilise the alpha phase andothers promote the formation of beta. Oxygen, carbon, nitrogen andaluminium promote the formationof the alpha phase; chromium,molybdenum, niobium, tin andvanadium promote the formation of beta. By suitable additions of theseelements it is possible to produce

four families of titanium alloys, dividedon the basis of microstructure, intocommercially pure titanium, alpha or near alpha alloys, alpha-beta alloysand beta alloys. ASTM designations,a simple numbering system, are acommonly used shorthand way of identifying the various alloys and both these and the alloy composition egTi-6Al-4V, will be used within thisarticle.

Commercially pure, unalloyed ASTM1 - 4 and 7 grades contain smallamounts of contaminants such asoxygen, nitrogen and carbon, typically less than 0.2%, and have mechanicalproperties matching those of agood quality low carbon steel. Thefewer contaminants, the lower is the tensile strength. The majority of thesealloys are used for their corrosionresistance. Welding is straightforwardand has little effect on the mechanical

properties in the HAZ and they aregenerally welded in the annealedcondition.

The alpha and near alpha alloys, typified by the Ti-5Al-2.5Sn alloy, haveultimate tensile strengths (UTSs) of 500-900MPa, 0.2% proof (PS) of 600-800MPa and elongations (El%) of around 18%. As with the commercially pure alloys the mechanical propertiesof this group are insensitive to heat

treatment. Weldability is good, thealloys being welded in the annealedcondition.

The alpha-beta alloys are sensitive toheat treatment, solution treatment

and ageing, increasing the strengthby 50% compared with the annealedcondition. The very high strengthalpha-beta alloys such as Ti-5Al-2Sn-2Zr-4Mo-4Cr may have a UTS of 1200MPa, PS of 1150MPa and an El%of 10. Weldability of the alloys within this group, however, is dependenton the amount of beta present, themost strongly beta stabilised alloysbeing embrittled during welding and,

although it is possible to restore someof the ductility by a post-weld heat treatment, this is often impractical.These very high strength, high betacontent alloys are therefore rarely welded. Contrast this with possibly the most frequently used alpha-betaalloy, Ti-6Al-4V (ASTM Grade 5) witha UTS of 950MPa, a PS of 850MPaand El% of 15. This alloy has goodformability, is readily workable, hasgood castability, excellent weldability

and could be regarded as the alloy against which to benchmark all others.

The fully beta alloys, eg Ti-13V-11Cr-3Al, have similar strengthsbut with slightly improved ductility, typically around 15% elongation. Thebeta phase is termed metastable – cold work or heating to elevated temperatures may cause partial transformation to alpha. The alloyshave high hardenability, very good

forgeability and are very ductile. Weldability is good, taking placewith the alloy in the annealed or solution treated condition although toobtain the full strength it is generally necessary to weld in the annealedcondition, cold work, solution treat and then carry out an ageing treatment.

Filler metals, all solid wires andmatching the composition of the

commoner of the alloys, are available, the relevant specifications being AWSA5.16/A5.16M:2007 Specification for

Job Knowledge109 Welding of titanium and its alloys

Part 1

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Technolog y Transfe r

5

titanium and titanium-alloy weldingelectrodes and rods and BS EN ISO

24034.2010 Welding consumables,solid wires and rods for fusionwelding of titanium and titaniumalloys. Although readily available, therange of consumables is somewhatrestricted with only fourteen or fifteencompositions being produced inaccordance with these specifications.

Weldability, as mentioned above, isin general very good. The exceptionis the high beta alpha-beta alloys.

The fundamental problem in welding titanium alloys is the eliminationof atmospheric contamination.Contamination of the weld metal and the adjacent HAZs will increase tensilestrength and hardness but may reduceductility to an unacceptably low valuesuch that cracks may occur even inconditions of only moderate restraint.The most likely contaminants areoxygen and nitrogen, picked up due to

air entrained in the gas shield or fromimpure shield gas, and hydrogen frommoisture or surface contamination.

The maximum tolerable limits in weldmetal have been estimated as 0.3%oxygen, 0.15% nitrogen and 150ppmhydrogen so scrupulous cleanlinessis essential for both parent metalsand filler wires. Degreasing the weldpreparation followed by stainless steel

wire brushing and a further degreaseis generally sufficient. Heavily oxidised

components may need to be pickledin a nitric/hydrofluoric acid mixture toremove the oxide layer. Degreasing of the filler wire for TIG welding shouldbe done as a matter of course and the cleaned wire handled with cleancotton gloves; grease and perspirationfrom the fingers can cause localcontamination and/or porosity. MIGwire should be ordered in a degreasedcondition, stored in clean dry

conditions and not left unprotectedon the shop floor.

During welding those parts of theweldment exposed to temperaturesabove 520OC will absorb oxygenand nitrogen and must therefore beprotected until they have cooledbelow this critical temperature.Fortunately heat conduction in titanium is low so the area affectedis limited in size and chill blocks can

be used to reduce this heated zoneeven fur ther. The molten weld pool isprotected by the normal gas shroudbut the cooling weld and its HAZwill need additional protection by theuse of a trailing shield with its ownprotective gas supply following alongbehind the welding torch. The back face of the weld also needs similar protection by the provision of anefficient gas purge.

Surface discolouration will give agood indication of the degree of

atmospheric contamination as shownin the the colour char t. Under perfectshielding conditions the weld willbe bright and silvery in appearance.Discolouration at the outer edges of the HAZ is not generally significantand may be ignored. As contaminationincreases the colour changes fromsilver to a light straw colour, then dark straw, dark blue, light blue, grey andfinally a powdery white.

The light and dark straw coloursindicate light contamination thatis normally acceptable. Dark blueindicates heavier contamination thatmay be acceptable depending on the service conditions. Light blue,grey and white indicate such a highlevel of contamination that they areregarded as unacceptable. In multi-pass welds the contamination willobviously affect any subsequent weld

runs so that surface appearance aloneis not a reliable guide to whether or not unacceptable contaminationhas occurred. A simple bend test isa reliable but destructive method of checking if the weld is unacceptably embrittled but note that the bendradius varies depending on theparticular alloy. For example, a 3t bendradius is used for testing a Grade 2weld but a 10t bend radius is usedwhen testing Ti-6Al-4V. Portable

hardness checks may also be carriedout on production items; this requiresknowledge of the hardness expectedin the specific alloy weld metal.

Part 2 of this article will consider some

of the other welding problems and

provide guidance on TIG and MIG

welding of titanium.

This article was written by Gene Mathers

TIG welds in commercially pure titanium sheet made with successively greater air contamination of the shielding

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Q A JoinITregister now

www.twi.co.uk

What is meant by single-pointmeasurement of fracture?

Where can I find informationregarding porosity in aluminium?

How do I select a consumablefor welding cast iron?

Digital imaging - it’s everywhere! After years of

continuous digital advancement we now take

it for granted. Nearly everyone owns a mobile

phone and the vast majority allow users to take

instant digital pictures or video footage and send

it anywhere in the world at the click of a button.

It was inevitable that digital imaging would infiltrate into

radiography and is already widely used in the medicalservices across the world. It has also been used for

industrial applications for a number of years now, but

how do we begin to assess digital radiographic systems?

CMOS and, CCD sensors, PSP imaging plates, TFTs to

name a few, can appear confusing to many traditional

film radiographers. However, the application of digital

systems is growing and industry including certification

bodies within non destructive testing are realising that the

training requirements for personnel asked to use such

systems cannot be covered adequately by traditional film

radiography certification. Further training specific to digitalimage acquisition is vital for the whole NDT industry.

Many clients are now asked ‘Can I substitute film radiography

for a digital radiographic system?’ by their suppliers. Often a

suspicious eye

is cast over

this question

although

the benefits

listed appear

attractiveand include:

reduced film

cost, no more

chemicals

and no more

archiving

nightmares

associated

with

traditional film radiography.

Some of the key questions being asked are:

• How good is the digital image?

• How can you control the quality?• How do you know if things are going wrong?

• What about security, can digital images be manipulated?

These are all valid questions that need an answer.

TWI has been conducting digital radiographic courses

and certification in digital radiography to EN 473 for over

a year, covering profile and tangential, welds and castings

applications.

Additionally, TWI can offer bespoke training for special

applications and company specific certification.

Scheduled courses will be delivered at TWI Technology

Centre (Nor th East) in Middlesbrough and TWI Abington

near Cambridge, and with these courses now concluding

in Level 2 cer tification exams for both PCN and CSWIP,

there has never been a better time to book your digital

radiography training with TWI.

Visit our website www.twitraining.com or contact

Customer Services on +44 (0)1223 899500

Digital radiography now PCN and

CSWIP approved!

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For further information on TWI,

visit the website at www.twi.co.uk

News in brief

Ninth International Friction Stir

Welding Symposium (9FSWS)

Von Braun Center - Huntsville,

Alabama, USA

15-17 May 2012 The Ninth International Friction Stir

Welding Symposium will be held at

the Embassy Suites Hotel - Von Braun

Center in Huntsville, Alabama, USA,

15-17 May 2012.

This symposium will provide the

latest information from industrial

and academic experts from around

the world in this rapidly growing

technology and provide a forum for

attendees to exchange views and

information on the current status of

friction stir related techniques.

A particular highlight of this event will

be a post-symposium industrial visit to

NASA - Marshall Space Flight Center.

This will be a unique opportunity

to visit one of the pioneering usersof FSW and to tour their facilities

housing a wide range of cutting-edge

equipment.

This symposium will be organised by

TWI Ltd on behalf of the Friction

Stir Welding Licensees Association,

in collaboration with Concurrent

Technologies Corporation.

Further information will follow over

the coming months.on the website

www.twi.co.uk/fsw

For additional information regarding

the Ninth International Friction Stir

Welding Symposium, please contact

Jonathan Martin:

Email: [email protected]

In a major expansion drive TWI South

East Asia is now offering HSE training

courses and consultancy services to

meet and service the growing demand

for quality health and safety training in

the Asia Pacific region.

TWI SEA now provides a range of internationally recognised accredited

training programmes including

NEBOSH, IOSH, IEMA, MEDIC First

Aid, and specialised tailored HSE

courses developed by TWI. This new

division will be headed by Mohamad

Darus bin Taib, TWI SEA’s General

Manager for Training & Certification.

TWI HSE is one of the largest

international NEBOSH and IOSH

providers and has built an enviable track record by achieving excellent

results, including producing the World’s

Best Student for the NEBOSH

International General Certificate of

the year.

TWI HSE is currently delivering

courses throughout the Middle East,

North Africa, Caspian Sea, India,

Pakistan and South East Asia.

For more information on HSE courses,

visit: www.twihsetraining.com and to

nd out more about the programme

in South East Asia, please contact

[email protected]

TWI South East Asia expands into

Health, Safety and Environment (HSE)

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European project to developinspection system for

counterfeit components

8

Connect is the

bi-monthly magazine

of TWIEditor:

Penny EdmundsonPhotography: Simon Condie

Production: Penny Edmundson

© Copyright TWI Ltd 2010

Articles may be reprinted

with permission from

TWI. Storage in electronic

media is not permitted.

Articles in this publication

are for information only.

TWI does not accept

responsibility for the

consequences of actions

taken by others after

reading this information.

This publication is also

available in alternativeformats. Please [email protected] to

request a copy.

Published byTWI Ltd, Granta Park,

Great Abington,

Cambridge CB21 6AL, UK

Tel: +44 (0)1223 899000

Fax: +44 (0)1223 892588

E-mail: [email protected]

www.twi.co.uk

TWI Technology Centre

(North East)

Tel: +44 (0)1642 216 320

Fax: +44 (0)1642 252 218

TWI Technology Centre

(Yorkshire)

Tel: +44 (0)114 269 9046

Fax: +44 (0)114 269 9781

TWI NDT Validation

Centre (Wales)

Tel: +44 (0)1639 873 100

Fax: +44 (0)1639 864 679

TWI Aberdeen

Tel: + 44(0)1224 691222

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Issue 169 November/December 2010

Counterfeit electronic components are

defined as ‘substitutes or unauthorised

copies, a product where the materials used

or its performance has changed withoutnotice, or a substandard component

misrepresented by the supplier’.

Counterfeit components are a growing

issue to the electronics industry and

the cost to electronics manufacturers

of inadvertently purchasing counterfeit

components includes lost yield, field failures,

product recalls and damage to reputation

as well as the all-important safety issue.

Despite taking extra precautions whensourcing components for safety critical

electronic systems, there have been

reports of counterfeit components entering

the supply chains in both the defence and

aerospace industries.

Dr Ian Nicholson, project leader for

ChipCheck, is asking if TWI members can

help.

He said: ‘To allow us to develop the

inspection system we need to obtain as

many electronic components as possible.

The source of the component will be kept

completely anonymous. Ideally these will be

unused, but could be par ts removed from

an assembly. We are interested in receiving

all package types and sizes to make sure

the system and the software recognition

is capable of comparing the range of parts

used in industry. The main focus will be

surface mount, however dual in-line parts

will also be assessed.’

The final goal of the project is to produce

a prototype inspection system to

automatically inspect components in their

original packaging.

If you are able to provide sample parts or

would like further information, then please

contact [email protected] .

On the 19 October 2010 the EU FP7 project ChipCheck began.

This two year project, involving eight partners comprising both

SMEs and research institutes and led by TWI NDT ValidationCentre (Wales), seeks to develop an inspection system for the

automatic detection of counterfeit electronic components at the

Goods Inwards point. Manufacturers are currently not able to

check all components at this stage.

Documents

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