A Novel Approach of Microstructure Refinement of TiAl in Laser Beam Welding

Grain refinement through borides is known to be suppressed when TiAl is welded with a laser beam. As β grains do not primarily nucleate on boride at a high cooling rate, a mixture of nitrogen and argon is applied as a protecting gas for the formation of TiN during solidification. The phase transform...

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Published inMetals (Basel ) Vol. 13; no. 1; p. 7
Main Authors Liu, Jie, Guo, Shun, Zhang, Peng, Ma, Tao, Wang, Zhuo, Wu, Tongli, Wang, Li, Wang, Kehong
Format Journal Article
LanguageEnglish
Published Basel MDPI AG 01.01.2023
Subjects
Alloys
Argon
Borides
Cooling rate
Ductility
Grain boundaries
Grain refinement
Heat
Intermetallic compounds
Laser beam welding
Lasers
Microstructure
Morphology
Nitrogen
nitrogen atmosphere
Phase transitions
Solidification
Spectrum analysis
TiAl alloy
Titanium aluminides
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Summary:Grain refinement through borides is known to be suppressed when TiAl is welded with a laser beam. As β grains do not primarily nucleate on boride at a high cooling rate, a mixture of nitrogen and argon is applied as a protecting gas for the formation of TiN during solidification. The phase transformation is changed correspondingly from Liquid → Liquid + β → β → α + β → α + γ+ β → α2 + γ + B2 to Liquid → TiN + Liquid → β+ TiN → α + γ + TiN → α2 + γ+ TiN. It is found that β grains prefer to nucleate heterogeneously on the suspending TiN in the melt with orientation relationship {111}TiN//{110}β, leading to refined β grains. α2 colonies that were thus modified into fine non-dendritic grains. The effects of nitrogen as a shielding atmosphere on the microstructure evolution of TiAl are elaborately studied.
ISSN:2075-4701
2075-4701
DOI:10.3390/met13010007