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Wire plus Arc Additive built multi-alloystructural component for the marineenvironment

Offshore structural steels generally conform to various designstandards, e.g. BS EN 10025. However, design flexibility is oftencompromised to maintain a single material grade. For complex bespokecomponents forgings/castings are often used, but are expensive andlogistically complicated. WAAM is a cutting-edge technology capable ofsignificant component design improvement, reduced delivery timethrough reduced material usage and environmentally sustainable.Material selection allows the use of different materials depending onthe application and stress analysis, reducing operating expenditures(Opex). A drawback of the technique is structure surface wavinessproduced by the deposition process which may cause undesirablestress concentration.

To understand the suitability of the WAAM processin developing bespoke parts/components to exploit design flexibility.However, for cost effective application further machining andprocessing needs to be optimised.

Introduction

• ER120S-G & ER90S-B3 are more sensitive to surface waviness ascompared to ER70S-6 that possesses some damage toleranceattributes (Fig. 6).

• EBSD analysis reveals moderate anisotropy in the WAAM alloys andthese properties could be advantageous for utilisation in gradedstructures (Fig. 8).

• The EDS line scanning at the ER90S-B3 /ER70S-6 interface reveals avariation of alloying element across the interface, the content ofchromium decrease significantly near the fusion line than that ofnickel with hardness measurements following the same trend(Fig.10)

• Notches associated with waviness serve as stress risers andtherefore reduce the fatigue life of the structure (Fig. 11).

• WAAM of multi grade possesses similar properties as single gradesand both mechanical properties meets the minimum required bystandard (Fig. 6&7).

• Ongoing work to determine fracture toughness and crack growthrate in single and multi graded WAAM structure for both machinedand as deposited condition is in progress.

Methodology

Results and discussion

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Unmachined Machined Unmachined Machined Unmachined Machined

ER120S-G ER120S-G ER70S-6 ER70S-6 ER90S-B3 ER90S-B3

Elo

ng(

%)

MP

a

UTS(Mpa) Rp(Mpa) Elong(%)

Summary and ongoing work

Wind turbinemain frame

Mild steel

High strengthsteel

Ultra fatigueresistance steel

Ultra wearresistance steel

=200 µm; Map4; Step=0.2709 µm; Grid1774x1330

Philip Dirisu- taiye.p.dirisu@cranfield.ac.uk, REMS Centre, Cranfield University, UK, MK43 0ALAcademic Supervisors: Dr. Supriyo Ganguly & Dr. Filomena MartinaIndustrial Supervisor: Juan Carlos Ceballos (Vestas)

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Max

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ss(M

Pa)

Number of cycle to fracture

ER70S-6 (Machinedcondition)

ER70S-6(Aswelded condition)

70% 0f Rp 70% of UTS 80% of UTS 90% of UTS 50% UTS 22.5% of PS

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Distance from the bottom of test piece(mm)

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ss(M

Pa)

Number of cycle to fracture

ER120S-G (Aswelded condition)

ER70S-6 (Aswelded condition)

Fig 10: Hardness variation and EDS line scanning at the ER90S-B3 /ER70S-6 interface of a mixed grade WAAM structure

=200 µm; Map4; Step=0.2709 µm; Grid1774x1331

=200 µm; Map4; Step=0.27 µm; Grid1780x1336

Fig 6: Average mechanical properties of machined Vs as- depositedcondition for WAAM ER70S-6, ER90S-B3 & ER120S-G – X direction

Fig 5: WAAM set up (a) & multi grade built structure (b)

WA

AM

Single grade

Machined ER70S-6 ER90S-B3 ER120S-G

As deposited

Peening ER70S-6 ER90S-B3 ER120S-G

Rolling

Multi grade

Machined ER120S-G/ER70S-6 ER90S-B3/ER70S-6 ER120S-G/ER90S-B3

As deposited

Peening ER120S-G/ER70S-6 ER90S-B3/ER70S-6 ER120S-G/ER90S-B3

Rolling

MIG-cold metaltransfer process

(CMT)

DepositionParameters

optimisation

Parallel + oscillatorydeposition strategies

InstrumentedWAAM for thermalcycles monitoring in

each layer

Microstructural+

metallurgicalcharacterisation

Static + dynamicmechanicalproperties

characterisation

project aims

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(ER70S-6 + ER90S-B3)HORZ

(ER90S-B3)HORZ (ER100S-G +ER90S-B3)HORZ

Elo

ng

(%)

MP

a

Rp(MPa) UTS(MPa) Elong(%)

ER70S-6

Fig 1: Project targeted component Fig 2: WAAM steel post processing

Fig 4: Test matrix

Fig 3: Sequence of experimental process

The methodology adopted for the project is highlighted in Fig.3. Fig.4 shows thetest matrix. The set up and built multi grade structure is shown in Fig 5 (a & b)

Fig 7: Mechanical properties of multi graded structure

Fig 9: Pole figure & inverse pole figure images of ER120S-G WAAM structure

ER90S-B3ER120S-G

Fig 8: Electron backscatter diffraction (EBSD) images of ER120S-G, ER90S-B3 & ER70S-6 WAAM structure

{111}Y0

X0

Pole Figure

[ER120 H-X(r) Site 6 Map Data 8.cpr]

Iron bcc (old) (m3m)

Complete data set

1721502 data points

Equal Area projection

Upper hemisphere

Half width:10°

Cluster size:5°

Exp. densities (mud):

Min= 0.32, Max= 2.22

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{111}Y0

X0

Pole Figure

[EK120 V-2 Site 4 Map Data 5.cpr]

Iron bcc (old) (m3m)

Complete data set

1857979 data points

Equal Area projection

Upper hemisphere

Half width:10°

Cluster size:5°

Exp. densities (mud):

Min= 0.07, Max= 3.20

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Z1001

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111

Inverse Pole Figure

(Extended)

[ER120 H-X(r) Site 6 Map Data 8.cpr]

Iron bcc (old) (m3m)

Complete data set

1721502 data points

Equal Area projection

Upper hemisphere

Half width:10°

Cluster size:5°

Exp. densities (mud):

Min= 0.66, Max= 1.34

Cr

ER90S-B3

ER120S-G

a) b)

Fig 11 : Effect of stress concentration on dynamic performance of WAAM steel machined in Z-direction, R = 0.1 , Freq = 15HZ