www.cranfield.ac.uk Wire plus Arc Additive built multi-alloy structural component for the marine environment Offshore structural steels generally conform to various design standards, e.g. BS EN 10025. However, design flexibility is often compromised to maintain a single material grade. For complex bespoke components forgings/castings are often used, but are expensive and logistically complicated. WAAM is a cutting-edge technology capable of significant component design improvement, reduced delivery time through reduced material usage and environmentally sustainable. Material selection allows the use of different materials depending on the application and stress analysis, reducing operating expenditures (Opex). A drawback of the technique is structure surface waviness produced by the deposition process which may cause undesirable stress concentration. To understand the suitability of the WAAM process in developing bespoke parts/components to exploit design flexibility. However, for cost effective application further machining and processing needs to be optimised. Introduction • ER120S-G & ER90S-B3 are more sensitive to surface waviness as compared to ER70S-6 that possesses some damage tolerance attributes (Fig. 6). • EBSD analysis reveals moderate anisotropy in the WAAM alloys and these properties could be advantageous for utilisation in graded structures (Fig. 8). • The EDS line scanning at the ER90S-B3 /ER70S-6 interface reveals a variation of alloying element across the interface, the content of chromium decrease significantly near the fusion line than that of nickel with hardness measurements following the same trend (Fig.10) • Notches associated with waviness serve as stress risers and therefore reduce the fatigue life of the structure (Fig. 11). • WAAM of multi grade possesses similar properties as single grades and both mechanical properties meets the minimum required by standard (Fig. 6&7). • Ongoing work to determine fracture toughness and crack growth rate in single and multi graded WAAM structure for both machined and as deposited condition is in progress. Methodology Results and discussion 10 15 20 25 30 35 40 200 300 400 500 600 700 800 900 1000 1100 Unmachined Machined Unmachined Machined Unmachined Machined ER120S-G ER120S-G ER70S-6 ER70S-6 ER90S-B3 ER90S-B3 Elong(%) MPa UTS(Mpa) Rp(Mpa) Elong(%) Summary and ongoing work Wind turbine main frame Mild steel High strength steel Ultra fatigue resistance steel Ultra wear resistance steel =200 μm; Map4 ; Step=0.2709 μm; Grid1774x1330 Philip Dirisu- [email protected], REMS Centre, Cranfield University, UK, MK43 0AL Academic Supervisors: Dr. Supriyo Ganguly & Dr. Filomena Martina Industrial Supervisor: Juan Carlos Ceballos (Vestas) 50 100 150 200 250 300 350 400 450 500 10 100 1,000 10,000 100,000 1,000,000 10,000,000 100,000,000 Max stress(MPa) Number of cycle to fracture ER70S-6 (Machined condition) ER70S-6(As welded condition) 70% 0f Rp 70% of UTS 80% of UTS 90% of UTS 50% UTS 22.5% of PS 50 100 150 200 250 300 350 400 0 5 10 15 20 25 30 Hardness HV Distance from the bottom of test piece(mm) ER90S-B3 ER70S-6 50 150 250 350 450 550 650 750 10 100 1,000 10,000 100,000 1,000,000 10,000,000 Max stress(MPa) Number of cycle to fracture ER120S-G (As welded condition) ER70S-6 (As welded 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- deposited condition for WAAM ER70S-6, ER90S-B3 & ER120S-G – X direction Fig 5: WAAM set up (a) & multi grade built structure (b) WAAM 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 metal transfer process (CMT) Deposition Parameters optimisation Parallel + oscillatory deposition strategies Instrumented WAAM for thermal cycles monitoring in each layer Microstructural + metallurgical characterisation Static + dynamic mechanical properties characterisation project aims 25 27 29 31 33 35 37 39 41 43 45 0 100 200 300 400 500 600 700 800 900 1000 (ER70S-6 + ER90S- B3) VERT (ER70S-6 + ER90S- B3)HORZ (ER90S-B3)HORZ (ER100S-G + ER90S-B3)HORZ Elong (%) MPa 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 the test 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-B3 ER120S-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 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 1 {111} Y0 X0 Pole Figure [EK120 V-2 Site 4 Map D 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 1 2 Z1 001 1-11 101 111 Inverse Pole Figure (Extended) [ER120 H-X(r) Site 6 Map 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