Challenge 1: Resistance to Weld Cracking
Many Ni-based alloys are susceptible to different weld cracking phenomena that can be sensitive to alloy chemistry. During the solidification of weld metal, the alloying elements segregate to either the liquid or the solid and cause local composition differences. Segregation of aluminium (Al), titanium (Ti), and/or niobium (Nb) causes local variances in gamma prime (γ′) and gamma double prime (γ′′) precipitation kinetics and volume fractions, leading to a loss of creep strength. Depending on alloy chemistry, this segregation can also cause formation of low melting point eutectics, which can then cause solidification cracking.
Challenge 2: Post Weld Heat Treatments
Segregation during solidification is typically unavoidable during welding. A solution heat treatment can be applied to smooth the composition gradients, but this is not always practical. Choosing the right time and temperature can be time-consuming when using a trial and error process.
Challenge 3: Pitting Corrosion Resistance
The segregation of alloying elements during solidification can also be detrimental to other properties, such as pitting corrosion resistance. For example, the segregation of molybdenum (Mo) during solidification can lead to local pitting corrosion in areas depleted of Mo, which can cause local corrosive attack.
Challenge 4: HAZ Liquation Cracking
Weldability challenges are not always limited to the weld metal. In the heat affected zone (HAZ), liquation cracking can occur depending on the alloy chemistry, weld thermal cycle, and the pre-existing microstructure.
How to Mitigate these Ni-based Alloy Weld Issues
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