Weldability Investigation of GTD-111 Nickel Base Superalloy by Wobbling Laser Welding Process

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Weldability Investigation of GTD-111 Nickel Base Superalloy by Wobbling Laser Welding Process

ارائه دهنده: Provider: Hossein Sadeghi

اساتید راهنما: Supervisors: Mohsen Sheikhi (Ph.D)

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Hamid Esfahani (PH.D) And Esmaeil Damavandi (Ph.D)

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 71

چکیده: Abstract: In the present project, the weldability of the nickel-based superalloy GTD-111 was investigated using the oscillating laser welding process. GTD-111, a nickel-based superalloy, is widely used in industries such as aerospace and power generation, particularly in gas turbine blades. Welding this alloy presents several challenges, the most significant being its susceptibility to cracking. This study examined the effect of applying laser beam oscillation during welding on the cracking sensitivity of this alloy. Oscillating laser welding was conducted with constant parameters: a laser focal point of 31 mm, laser power of 8 W, laser frequency of 200 Hz, and oscillation amplitudes of 0, 0.25, 0.75, and 1.25 mm, at three speeds of 6.5, 8.8, and 11.5 mm/s. A linear scanning pattern was used for laser oscillation. Optical microscopy and scanning electron microscopy (SEM) were utilized for examinations. JMatPro software was employed to analyze microstructure and crack sensitivity, while Excel and Digimizer software were used for calculations. Microstructural analysis revealed that the weld profile width increased with the oscillation amplitude from 0 to 1.25 mm. At a speed of 6.5 mm/s, the weld width increased from 1.64 to 2.33 μm; at 8.8 mm/s, it increased from 1.48 to 2.05 μm; and at 11.5 mm/s, it increased from 1.24 to 2.03 μm. Weld penetration depth remained constant with increasing oscillation amplitude across all samples, except for the sample with an oscillation amplitude of 1.25 mm at 11.5 mm/s, which exhibited reduced penetration due to incomplete fusion. Weld profile area analysis showed an increase across all samples except for the one with a 1.25 mm amplitude and 11.5 mm/s speed. Microstructural analysis of the weld pool identified phases such as the γ matrix, MC carbides, MB2 phase, γ' phase, η phase, ϭ phase, M3B2, and M23C6. In the weld zone, planar growth, cellular-dendritic, and dendritic microstructures were observed. Increasing the oscillation amplitude from 0 to 1.25 mm resulted in the planar growth zone width increasing from 3.22 to 6.49 μm. Higher oscillation amplitudes reduced dendritic spacing (SDAS and PDAS), leading to finer structures. Calculations showed that the thermal gradient (G) increased with higher oscillation amplitudes. Solidification cracking sensitivity decreased with the application of oscillation. According to the Modified Feurer’s criterion, reducing the length of the crack-sensitive zone reduces cracking sensitivity. Oscillation increases the thermal gradient (G), shortens the crack-sensitive zone, and thus reduces solidification cracking sensitivity. However, the Sindo kou criterion could not predict the effect of the process on cracking sensitivity.

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