A comparative study on the transient liquid phase bonding of gamma prime (γ’)-strengthened cobalt- and nickel-based superalloys
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Date
2019
Authors
Anyanwu, Chidinma
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Abstract
Cobalt-based superalloys have been used for several decades in manufacturing various gas turbine engine components because of their excellent high-temperature creep and fatigue strengths and resistance to hot corrosion attack. The recent discovery of the γ’ strengthening phase in cobalt alloys has opened up opportunities for its use in high-temperature applications. It is, however, known that alloys containing a significant amount of aluminum and titanium have been found to be difficult to weld due to their susceptibility to cracking. Efforts to overcome this challenge led to the development of the transient liquid phase (TLP) bonding technique. The objective of this research is to study and compare the effects of bonding time and temperature on the joint microstructure of TLP bonded cobalt- and nickel-based aerospace superalloys using Nicrobraz 150 (Ni-Cr-B) interlayer. The results show that the rate of isothermal solidification is faster in the Ni-based superalloy which can be due to the higher boron diffusivity in nickel than in cobalt. However, at higher temperatures, the diffusion-controlled bonding process is completed faster in the cobalt alloy, despite the lower diffusivity in the alloy. This could be attributable to the liquidus composition of boron in the cobalt alloy being closer to the eutectic value resulting in a smaller volume of liquid produced in the joint as compared to the nickel alloy. This work shows that TLP bonding can be used for joining the new γ’-strengthened Co-based superalloys and under certain conditions, the process may be more efficient in the new Co-based superalloys compared to existing Ni-based superalloys.
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Keywords
Superalloys, TLP bonding