Welding of Ti-6Al-4V: Influence of welding process and alloy composition on microstructure and properties
Doktorsavhandling, 2018
The welding processes compared were electron beam welding, laser beam welding, plasma arc welding and TIG welding. High energy beam welding processes rendered a finer weld microstructure in comparison to the coarser microstructure produced by arc welding processes. The finer weld microstructure was found to be beneficial for tensile ductility and low cycle fatigue performance. Porosity was observed in welds produced by all the processes. Large pores and pores located close to the specimen surface the most detrimental to the fatigue strength. Fatigue life in the welds produced by arc weld processes was more sensitive to porosity than in the high energy beam welds. The finer microstructure has a higher resistance to micro crack initiation and growth which contributed to the better fatigue performance of welds produced by electron beam welding and laser beam welding.
The alloy composition had a significant influence on the microstructure of the welds and the formation of defects. A small boron addition induced significant grain refinement in weld in boron alloyed material. Narrow columnar prior-β grains were formed in the fusion zones of the boron alloyed welds. The α colonies and α plates were also refined, as compared to the standard Ti-6Al-4V welds. In the cast base material, the TiB particles were located along the prior-β grain boundaries restricting the grain growth in the heat affected zone. In the fusion zone of welds, TiB particles had decreased in size and formed networks of stripes along the interdendritic regions. EBSD combined with prior-β grain reconstruction was an effective method to reveal the prior-β grain structure in the different weld zones. A significant batch to batch variation in amount of porosity was observed in laser welding of Ti-6Al-4V. The most significant factors affecting formation of porosity were the material batch, pulse length and welding speed. The material batches that were most susceptible to formation of porosity had increased amount of carbon and oxygen. The formation of porosity could be minimized in all material batches by optimizing the welding parameters.
fatigue
microstructure
Ti-6Al-4V
porosity
welding
defects
Författare
Sakari Tolvanen
Yt- och mikrostrukturteknik
Fatigue strength dependence on microstructure and defects in Ti-6Al-4V welds
Proceedings of the 13th World Conference on Titanium,;(2016)p. 311-315
Paper i proceeding
TIG welding and laser welding of boron alloyed Ti-6Al-4V
Proceedings of the 10th International Conference on Trends in Welding Research,;(2016)p. 321-324
Paper i proceeding
Tolvanen, S., Pederson, R., Klement, U. Microstructure and mechanical properties of Ti-6Al-4V welds produced with different processes
Microstructure and Porosity of Laser Welds in Cast Ti-6Al-4V with Addition of Boron
Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science,;Vol. 49(2018)p. 1683-1691
Artikel i vetenskaplig tidskrift
Tolvanen, S., Germain, L., Pederson, R., Klement, U. Phase transformation mechanisms in boron alloyed Ti-6Al-4V weld studied using beta grain reconstruction
Tolvanen, S., Johansson, J., Pederson, R., Klement, U. Batch to batch variation in formation of porosity in laser welding of Ti-6Al-4V
The welding processes compared were electron beam welding, laser beam welding, plasma arc welding and TIG welding. High energy beam welding processes produced a finer weld microstructure in comparison to the coarser microstructure produced by arc welding processes. The finer weld microstructure was found to be beneficial for tensile ductility and low cycle fatigue performance. Porosity was observed in welds produced by all the processes and this caused variation in the fatigue performance of the welds. Large pores and pores located close to the specimen surface the most detrimental to the fatigue strength. Fatigue life in the welds produced by arc weld processes was more sensitive to porosity than in the high energy beam welds. The finer microstructure has a higher resistance to micro crack initiation and micro crack growth which contributed to the better fatigue performance of welds produced by laser beam welding and electron beam welding.
The chemical composition of the base material had a significant influence on the microstructure of the welds and the formation of defects. A small boron addition induced significant grain refinement in boron alloyed welds. Narrow columnar prior-β grains were formed in the fusion zones in the welds in boron alloyed materials. The α colonies and α plates were also refined, as compared to the standard Ti-6Al-4V welds. TiB particles located in the prior-β grain boundaries restricted the grain growth in the heat affected zone. A significant batch to batch variation in amount of porosity was observed in laser welding of Ti-6Al-4V. The material batches that were most susceptible to formation of porosity had increased amount of carbon and oxygen. The formation of porosity could be minimized in all material batches by optimizing the welding parameters.
Bildande av defekter vid svetsning och deras inverkan på mekaniska egenskaper hos Ti-6Al-4V och Ti-6Al-2Sn-4Zr-2Mo
VINNOVA (2013-01148), 2013-08-01 -- 2017-06-30.
Ämneskategorier
Bearbetnings-, yt- och fogningsteknik
Annan materialteknik
Metallurgi och metalliska material
Styrkeområden
Materialvetenskap
ISBN
978-91-7597-771-3
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4452
Utgivare
Chalmers
Virtual Development Laboratory, Hörsalsvägen 7A
Opponent: Prof. Lars Pejryd, School of Science and Technology, Örebro University, Sweden.