Waspaloy is nominally composed of Nickel (58%), chromium (19%), cobalt (13%), molybdenum (4%), titanium (3%), and aluminum (1.4%). Waspaloy maintains its exceptional strength at extremely high temperatures in the range of 1400-1600°F7 (60-870°C). It also has excellent corrosion and oxidation resistance.
Waspaloy is precipitation hardening (age hardening) and austenitic in its structure.
Waspaloy is similar to Inconel 718, but it exhibits higher creep rupture strength at high temperatures and slightly less short time hot tensile strength.
Electron Beam Welding Waspaloy
Waspaloy can be welded, but it requires expertise and experience, and it is not a task to be undertaken lightly. It should be welded in the solution annealed condition. Further, Waspaloy does work harden, so the order of machining and joining processes involved is critical to success part outcomes. After welding, rapid cooling treatment in a solution is also advised to minimize the chance of age cracking.
Age and strain cracking is a common problem when welding Waspaloy. EB welding is the preferred welding process because of the high power availability of the process, which results in rapid melting of the alloy, a narrow fusion-zone (FZ), and a small minimized heat-affected zone (HAZ), which reduces distortion and residual stresses. EB welding happens in a vacuum, which mitigates material contamination and yields pure welds at any depth of penetration.
As always, it is critical that all joint areas are thoroughly cleaned before EB welding.
Here are some common sense guidelines that should be followed when preparing Waspaloy parts for EB welding:
- Clean cloths should be used for cleaning Waspaloy surfaces with solvents, such as paper towels or cheese cloth.
- When blowing debris off a joint, bottled gas, such as argon or nitrogen, should be used to maintain a clean weld area. Compressed shop air should not be used because it could contaminate the area.
- Solvents should be used to clean parts and joints before using a wire brush in order to avoid embedding hydrocarbons and other contaminates into the joint potentially introduced by the brush. Therefore, the solvents are far more effective.
- New or recently cleaned stainless steel brushes should always be used when cleaning the weld area, as using old or dirty stainless steel brushes could contaminate the joint areas.
- By-products from etching may drastically weaken joints by altering the chemical composition of the weld pool. Therefore, if you happen to weld an etched surface, it is crucial you clean it with your stainless steel wire brush before further processing the part.
- All wire brushes and scraping, filing and cutting tools should be cleaned frequently.
Pre-Treating and Fixturing Waspaloy
Proper pre/post weld heat treatment minimizes the risk of liquation cracking in Waspaloy due to EB welding. As mentioned earlier, some of EB welding’s assets include high energy-density, deep penetration, narrow welding seam and small HAZ. These are all advantageous when welding Waspaloy because of Waspaloy’s ability to retain integrity in high pressure and heat environments. As always, with EB welding, joint-fixturing should be done with extreme care and precision. Spaces or gaps in the joint cause less energy to be directed into the weld and will result in a weaker joint.
Joints produced by EB welding adhere to slightly varied and stricter standards because of EB welding’s precision and the fact that it does not require a filler. This includes:
- Butt Joint:
- This joint requires a fit-up tolerance that is 15% of the material thickness.
- Less than 25% of the material thickness for misalignment and out-of-flatness of parts is necessary.
- It is critical that sheared edges, when present, are straight and square.
- Lap Joint (burn-through or seam weld):
- In order to maximize weld penetration and speed, there can not be a significant space between the pieces that will be welded.
- Fillet Joint:
- This joint demands square edges and a good fit-up.
Waspaloy® is a registered trademark of Haynes Int.