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Title: Joining lightweight dissimilar alloys by using electron beam welding
Author: Moosa, Affaan
ISNI:       0000 0004 7972 0122
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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An investigation was carried out to study the ability to carry out dissimilar welding between Ti-6Al-4Valloy and commercially pure vanadium alloy. Electron beam melting machine (EBM) was adopted for EBW for the dissimilar welding process using an Arcam S12 system. A promising beam setting was generated using the design of experiment (DoE). DoE normalised parameters and discrete parameters were suggested to find the best beam welding setting. Using different normalising approaches helped to establish a full penetration weld with acceptable characteristics: weld root and weld undercut when set II was applied. Powder technology means and Spark Plasma Sintering was employed to design a filler metal to be used in dissimilar welding. Based on the microstructures and mechanical analysis, the designed filler metals Ti/V, Ti/V2 and Ti/V3 were selected as the designated interlayers to be prefixed in the joints between titanium base metal (Ti-BM) and vanadium base metal (VBM) in the pre-welding process. Dissimilar welding was performed based on the best beam parameters obtained from the beam optimisation methods. A successful full penetration weld was achieved between Ti-6Al-4V and CP-V alloys directly, without filler metals, which offered a tensile strength reaching to 282 MPa. When the 5 mm thin interlayer was added to the welding zone, the welds W1, W2 and W3 achieved strength close to that of the non-filler weld AW0. The hardness measurements for the welding zone (WZ) revealed increments in hardness values when the V content was increased in the WZ, reaching a maximum value of 345 HV1 for the WZ of weld type W2. The W2 weld sample, also, showed superior strength, reaching to ~270 MPa. The presence of solid-solution phase βTi-V reduced the hardness values from 375±5 HV1 in the case of the keyhole titanium weldtracks to about 354 HV1 in the WZ of the Ti-V dissimilar joint. Hardness measurements showed that the highest and lowest hardness values were in the titanium heat affected zone (Ti-HAZ) and vanadium heat affected zone (V-HAZ), respectively. Additionally, tensile tests confirmed that material failure occurred in the base metal with lower mechanical properties, i.e. vanadium, and not in the weld joint. Necking condition was observed in the V-HAZ in all the tensile samples with and without the filler metals, and as the failure took place outside the WZ this suggests that the attempt to carry out dissimilar welding between Ti-6Al-4V alloy and CP-V alloy was successful.
Supervisor: Todd, Iain ; Wynne, Brad Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available