Welding Nickel-Based Superalloys

nickel based superalloys

Manufacturers recognize superalloys for their excellent performance even at temperatures near the melting point. For this reason, nickel-based superalloys are particularly desirable in the aerospace and nuclear industries. However, meeting design criteria can be difficult due to the significant challenges of welding nickel-based superalloys. 

To ensure reliable, high-quality welds, manufactures and technicians should explore the unique properties of nickel, its alloys, and their weldability. 

Nickel-Based Superalloys

Most nickel-based superalloys combine nickel with other metallic or non-metallic alloying elements such as iron (Fe), cobalt (Co), chromium (Cr), molybdenum (Mo), tungsten (W), aluminum (Al), titanium (Ti), carbon (C), niobium (Nb), and more. Nickel-based alloys can either be solid solution strengthened or precipitate strengthened. The solid solution strengthened sheet alloys such as Hastelloy X are generally used for moderate strength applications and have Cr, Mo, W, and Fe as alloying elements. The primarily used precipitate strengthened Ni-based alloys have Ti and Al as essential solutes with 10-20% Cr content and small amounts of Zr, C, Mo, B, and W. 

Nickel-based alloys can be categorized into the following microstructural phases:

To ensure pipe welding consistency, operators should weld continuously around the pipe with controlled arc, feed, heat input, and speed. However, even for welders with years of experience, “human error” is possible. Additionally, large-diameter, thick-wall piping is impossible to weld in one continuous pass. Resulting inconsistencies can give rise to weld defects such as lack of penetration, inclusions, cracks, porosity, undercutting, splattering, and more.  Factors that contribute to manual pipe welding challenges include:

  • Gamma (𝛾): The gamma phase is generally a solid solution strengthened with alloying elements like C, Cr, Mo, Ti, Al, and W. The 𝛾 matrix has a face-centered cubic (FCC) and makes up the austenitic phase of the Ni-based alloy. 
  • Gamma prime (𝛾’): The gamma prime is the strengthening phase of the alloy. Addition of Ti and Al support aids in the formation of 𝛾’ precipitates, which strengthens and stabilizes the 𝛾 matrix. The addition of Co increases the solubility temperature of 𝛾’, making the alloy able to withstand high temperatures.  
  • Gamma double prime (𝛾’’): 𝛾’’ phase has a body-centered tetragonal (BCT) structure and supports the strengthening of nickel-based superalloy when the temperature is less than 650°C.
  • Carbide: Carbide formation occurs as the carbon combines with alloying elements like Ti. The effect of carbide in nickel-based alloy may not be advantageous in most cases; however, depending upon the amount of carbide, it is possible to stabilize a high-temperature deformation in the alloy. 
  • Topologically close-packed (TCP) phase: TCP has a plane plate-like microstructure that is generally brittle and not desirable for nickel-based alloy. TCP combines 𝛾 and 𝛾’, which affects the mechanical strength and can develop defects like cracks in the alloy.

Welding Challenges for Nickel-Based Alloys

When compared to other metals, nickel-based superalloys provide an excellent response against high temperatures. This trait, combined with their inherent strength, makes nickel-based superalloys a standard choice in aerospace and power generation turbines. However, the weldability of this alloy can be a serious problem, especially for precipitate strengthened alloy.

  • Alloying elements with low melting points such as sulfur or lead can cause embrittlement in the metal during welding.
  • Carbide precipitation can result in the development of cracks.
  • Stress in the heat-affected zone (HAZ) can initiate liquation cracks.
  • Incorrect interpass temperature can leave the metal without adequate fusion. 

Tungsten Inert Gas (TIG) welding is the most suitable process for welding nickel-based superalloys. The excellent heat input control minimizes the HAZ, which reduces the risk of grain growth and, consequently, the risk of cracking. Further, inert gas shielding can prevent oxidation while forming the pure weld. Compatible filler materials containing Ti, Al, and Nb with TIG welding can further minimize the risk of cracking or the development of pores. These positive results can be further enhanced with orbital welding

Orbital TIG Provides Reliable Results

Superalloys with high-end performance ability require a welding solution that can foster its properties and boost efficiency. Automated welding techniques like orbital welding can ensure that welding procedures are properly implemented. The control, consistency, and repeatability available with an orbital welding process ensure a high-quality weld with each pass. The orbital weld head enables proper weld penetration while the remote monitoring system allows weld parameter optimization for welding nickel-based superalloys. By maintaining the corrosion resistance and strength of nickel-based superalloys, orbital TIG welding helps manufacturers achieve productivity gains and consistent, reliable results.  


Arc Machines, Inc., with decades of expertise in creating high-quality, precision welds, can provide you with a high-end solution for welding nickel-based superalloys. Arc Machines welcomes you to explore our advanced welding technology processes and equipment. Contact us to arrange a meeting to discuss how we can address your welding needs.