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How To Weld Nickel Alloys
Nickel alloys have exceptional corrosion resistance, even at high temperatures, which makes them a perfect candidate for many critical applications. They are also quite expensive, and some parts produced from nickel alloys, like aircraft parts, can be of high value.
So, knowing how to weld nickel alloys is crucial to prevent costly mistakes. Fortunately, welding nickel alloys are not very challenging, but these alloys do have their quirks to be aware of. You could easily make brittle welds with a few simple mishaps. So, while nickel alloys are highly endurant in service, they are sensitive and require a careful welding approach.
Tig Welding Nickel Alloys
Photo by @sburpee (TikTok)
This article will teach you how to weld nickel alloys without cracking, which welding processes to use, the filler metal selection, and the different types of nickel alloys.
Challenges of Welding Nickel Alloys
Nickel alloys are prone to porosity, cracking, contamination, and oxide inclusions. This material is not forgiving, so you better treat it right, or those welds are not going to stick. If the weld fails, it's almost always necessary to mechanically remove all weld metal and re-do everything again. So, mistakes when welding nickel alloys can cause a bottleneck for any welding business. The better your understanding of this material and the better your standard operating procedures are, the more efficient you'll be at joining nickel alloys.
Porosity
Like mild steel, nickel alloys can develop porosity if the oxygen and nitrogen from the atmosphere are trapped in the weld. However, you must also worry about the surface hydrogen presence with nickel alloys. Therefore, it's not a bad idea to slightly preheat the welded part if you suspect any moisture has condensed on the metal's surface.
But here is the kicker: you can actually use up to 10% hydrogen in your shielding gas to reduce the chances of hydrogen porosity. Sounds crazy, but it works. The bubbles of the hydrogen will gather up the diffused hydrogen from the metal. However, if you decide to experiment with a hydrogen shielding gas, don't exceed the 10% content.
Hydrogen Porosity
Source: https://www.insidemetaladditivemanufacturing.com/blog/hydrogen-pore-formations-in-alsi10mg-processed-by-slm
You must use adequate shielding when MIG or TIG welding the nickel alloys, and it's helpful to use a larger shielding cup size when TIG welding to improve shielding gas coverage. As little as 0.025% nitrogen in the weld pool will cause porosity. So, maximum shielding gas coverage is vital. Ensure that the work environment doesn't have any wind drafts. In addition, gas purging is crucial when making critical welds.
Surface Oxide Inclusions
Nickel alloys often contain aluminum, titanium, chromium, and other elements in small quantities but large enough to produce surface oxides. These oxides melt at a higher temperature than the base metal underneath. So, unless you remove these oxides before welding, they'll get stuck in the weld puddle and make the joint quite weak. Think of them as hard pieces of metal that were just kind of laid inside the weld pool without actually melting. Such inclusions represent the hard spots that can easily lead to weld cracks.
Nickel alloy surface oxides should be removed with abrasive grinding or machining. Using a stainless steel brush will likely not suffice — you'll just polish up the oxides on the surface instead of removing them.
Remove nickle alloy surface oxides by grinding.
Source: https://www.adorwelding.com/wp-content/uploads/2021/07/E-Weldone-Letter-NOV-15-R3.pdf
If you are making a multipass weld, don't forget to remove the surface oxides between each pass. Surface oxides produced at high temperatures are even more detrimental, so each welding pass should be cleaned with an angle grinder. This is even more important to keep in mind if repairing a nickel alloy part that was exposed to high heat during its service life. For example, jet turbine engine parts can have oxides that must be removed before welding.
Be careful of using compressed air when grinding between passes to clean the beads. The compressed air can contain moisture, which brings us back to the issue of hydrogen presence. It's best to avoid using any compressed air altogether.
Weld Puddle Sluggishness
If someone ever sits you down at a welding table, hands you a TIG torch, a filler metal, and places a butt weld joint for you to fuse without letting you know that it's a nickel alloy, how will you know what material you are welding? The answer is simple — if the puddle is sluggish and dense, the chances are high that it's a nickel alloy.
Unlike stainless steel or mild steel, nickel alloys' puddle doesn't flow freely. It feels like a sluggish goo that's more challenging to navigate into the joint. As a result, you can easily create an overly convex weld bead with a poor toe blend into the surrounding metal.
TIG welding copper nickel alloy and its weld puddle sluggishness. (2:10-2:20)
Source: https://www.youtube.com/watch?v=abr7gMdAlkU
It's a good idea to grind the joint into a 60-80 degree V-butt configuration to help direct the weld puddle flow into the joint instead of making a lumpy bead.
Cracking
Nickel alloys are prone to various types of weld and heat affected zone (HAZ) cracking, but the most prominent cracking issue results from weld pool contamination. The worst element to introduce to nickel alloys is sulfur, but phosphorus, lead, zinc, cadmium, tin, boron, silver, bismuth, and other elements with a low melting point can cause hot cracking.
Many oils used for cutting and machining contain sulfur, and other shop processes and tools can introduce metals like lead or zinc. So, be extra careful of cross-contamination because nickel alloys will become brittle if the weld pool is contaminated.
Welding Crack
Source: https://www.adorwelding.com/wp-content/uploads/2021/07/E-Weldone-Letter-NOV-15-R3.pdf
What Types of Nickel Alloys Are Out There
There is a huge number of nickel alloys, and each has some unique characteristics, but many share similar properties.
The most widely welded nickel alloy is the pure nickel 200 and nickel 201. They are both corrosion-resistant, but nickel 201 has better resistance to carbon precipitation when used at temperatures higher than 315°C (600°F).
Nickel 201 vs Nickel 200
Source: https://blog.thepipingmart.com/metals/nickel-201-vs-nickel-200-whats-the-difference/
Weld with inconel alloy 600.
Photo by @jacobholcombe61 (TikTok)
Most of what we are about to discuss below can be applied to various nickel alloys. But, you should always consult industry codes when welding anything critical. For a detailed description of every nickel alloy, check out the book "Welding Handbook, Volume 5, Materials And Applications Part 2," by the American Welding Society.
Source: https://www.aws.org/publications/page/welding-handbook-9th-edition-volume-5
How To Preclean Nickel Alloys Before Welding
Since the surface presence of low melting point materials like sulfur and lead can cause nickel alloys' embrittlement, pre-cleaning before welding is crucial.
You must clean the nickel alloy surface from oils, paints, cutting fluids, crayon markings, polishing substances, grime, dirt, and cross-contamination from other metals in the shop.
It's imperative to avoid cross-contaminating via grinding belts, hammers, cutting tools, and abrasives. Even a dirty rag can contaminate the weld and cause post-weld cracking to occur.
Since nickel alloys are often employed in food processing facilities and other industries where the parts are exposed to chemicals, it's vital to clean the element from any residual chemicals or fatty acids before repairing it by welding.
Clean the oils and paints by using degreasing solvents and alkaline cleaners. Then, remove the surface oxides we discussed earlier using the carbide deburring tools because they are most likely to completely remove the oxides.
Photo by @michaelagrademechanic (TikTok)
Filler Metal Selection For Welding Nickel Alloys
You should generally stick to filler metals that are close to the chemical composition of the welded nickel alloy. But you can also overmatch it for improved corrosion resistance in the weld zone.
For detailed specifications of nickel alloy filler metals, consult AWS A5.14 specification for nickel and nickel alloy bare welding electrodes and rods book.
The table below describes the most commonly used bare electrode filler metals for welding nickel alloys:
|
Filler Metal Selection For Welding Nickel Alloys |
|||
|
Welded Alloy |
Filler Metal AWS Designation |
Additional Information |
|
|
Pure Nickel |
ERNi-1 |
Contains a certain amount of titanium to control porosity |
|
|
Nickel copper |
ERNiCu-7 |
Used for many nickel copper alloys |
|
|
ERNiCU-8 |
This filler metal age hardens with heat treatment |
||
|
Nickel chromium iron |
ERNiCr-3 |
Also works for surfacing steel and joining steel to stainless or nickel-based alloys |
|
|
ERNiCr-7 |
Excellent resistance to high temperature oxidation, sulfidation, and carburization |
||
|
ERNiCrFe-5 |
Provides excellent resistance to high welding stress cracking. Great for welding thick sections |
||
|
ERNiCrFeAl-1 |
Particularly resistant to metal dusting in petro-chemical applications |
||
|
Nickel chromium molybdenum |
ERNiCrMo-3 |
Recommended for operating temperatures from cryogenic to 1000°F (540°C) |
|
|
Nickel molybdenum |
ERNiMo-2 |
Also used to clad steel with nickel-molybdenum metal |
|
|
ERniMo-8 |
Used for welding steel with 9% nickel |
||
Welding Process Selection
You can weld nickel alloys using all arc welding processes, including shielded metal arc welding (SMAW), but we highly recommend sticking to TIG and MIG welding to achieve the best results. Furthermore, we specifically recommend using a TIG welding process because it provides the best puddle control and weld aesthetics.
MIG Welding Nickel Alloys
MIG welding nickel alloys is more efficient than TIG welding because it's easier, faster, and allows you to weld thicker sections. However, MIG welds are less likely to look aesthetically pleasing, unlike TIG welds.
Short-Circuit Arc Transfer
It's most efficient to use a standard short-circuit arc transfer when MIG welding thin sheets of nickel alloys. Short-circuit arc won't input too much heat, and you may avoid excessive distortion or burn-through. However, there will be more spatter, and your weld beads may be more convex, which requires post-weld grinding and can prolong your work hours. In addition, welding thick nickel alloys will likely suffer from a lack of fusion when using short-circuit transfer.
Spray Transfer
The spray transfer provides a much higher deposition rate and heat input, so you shouldn't set your MIG welder for spray transfer when welding anything under 0.25 inches thick. You'll get a more stable arc and less spatter, but the spray transfer works best for thicker joints.
Pulsed MIG Welding
The pulsed MIG welding offers the best of both worlds — it provides more power, but its not likely to burn-through the thin materials. You can learn more about how pulsed MIG welding works in our separate article. But the gist of it is that the pulsed MIG welder, like our YesWelder YWMP-211P, alternates between the high and low amperage output to provide a high deposition rate and penetration but with a less fluid puddle so that you have more control over it. Therefore, we recommend pulsed MIG welding for nickel alloys, but you can also use a standard short-circuit transfer; your welds may not be as pretty, but short-circuit works well most of the time. However, if you need to clad metal with nickel alloys, we recommend sticking with either spray transfer or pulsed MIG welding, and avoiding short-circuit altogether.
YesWelder YWM-211P Double Pulse Aluminum MIG Welder
Shielding Gas Selection
Use 100% argon as a shielding gas. You can mix argon with helium, but expect significantly wider and flatter weld beads with a reduced depth of fusion. Avoid pure helium because you'll get excessive spatter and erratic arc. DO NOT use standard MIG welding gas like 75/25 Ar/CO2 mixture because nickel alloys are far more likely to oxidize and contaminate the weld.
TIG Welding Nickel Alloys
Gas tungsten arc welding (GTAW), or otherwise known as TIG, is a far superior arc welding method than any other for welding nickel alloys. If you are a skilled TIG welder, you can achieve beautiful weld beads and much more uniform weld fusion and bead width.
TIG welding is a widely applied welding process for joining nickel alloys. Like, if you asked all welders you know which welding process they would use for nickel alloys, chances are high that the majority would immediately respond with "TIG, no doubt." While more challenging from the technique standpoint, TIG offers better precision and weld quality.
Tig welding copper nickel pipe.
Photo by @eatsleepweld90 (TikTok)
You should use TIG welding for nickel alloys whenever you weld thin materials, need a high-quality finish, and when making a root pass of a joint with an inaccessible back of the weld.
The direct current electrode negative (DCEN) setup is used to TIG weld nickel alloys. You can use standard DC TIG or a pulsed TIG welder when welding very thin sheets to prevent burn-through. Pulsed TIG welding is also beneficial for pipe root joints. Use high-frequency start when TIG welding nickel alloys to avoid contamination.
Arc Starting
Using a scratch or lift TIG start may leave tungsten residue particles on the nickel alloy's surface and cause weld contamination. If your machine doesn't support HF start, you can just initiate the arc on a scrap piece of metal adjacent to the joint and move the arc to the nickel alloy joint. That way, you'll prevent joint contamination. Mind you, this is not a perfect way to start the arc, so we recommend getting an HF capable TIG machine, like the YesWelder TIG-250P or the YesWelder YWT-200DC.
TIG-250P DC Pulsed TIG Welding Machine with HF Start
YesWelder YWT-200DC Lift TIG Spot TIG Welder
Tungsten Selection
You can use standard thorium tungsten electrodes to weld nickel alloys.
WT20 Series 2% Thoriated TIG Welding Tungsten Electrode
Pure tungsten rods also work well, but cerium or lanthanum alloyed tungsten provide better results and offer a longer life. The thoriated tungsten is radioactive, so you must be careful when grinding it not to inhale its dust. But, lanthanated or ceriated tungsten are non-radioactive and safe to use.
WL20 Series 2% Lanthanated TIG Welding Tungsten Electrode
Cerium tungsten works best at lower amperages, so we recommend it for welding thin joints.
WC20 Series 2% Ceriated TIG Welding Tungsten Electrode
Shielding Gas Selection
We recommend using a 100% argon shielding gas for TIG welding nickel alloys. You can add some helium to the mix, but again, you'll get a more erratic arc and a wider bead profile.
Using a large enough TIG torch cup is vital to provide efficient gas shielding over the joint. As we discussed earlier, you must provide maximum protection over the molten nickel alloy metal. Otherwise, you are risking oxidation and porosity.
Conclusion
Welding nickel alloys is not challenging technique-wise; you'll get the hang of it quickly if you have experience with stainless, aluminum, or other exotic metals. However, providing maximum cleanliness and shielding gas coverage could pose a challenge, depending on how your shop operates.
Make sure there is no cross-contamination with other metals, clean the joint well, and remove the surface oxides, and you should have relatively good results. However, there are many nickel alloys, and some are highly specialized. Our article was a general overview of how to weld nickel alloys. Please do consult with an engineer if you are working on something critical and you are welding an alloy from special groups.
🧐How To Weld Nickel Alloys - FAQ
1. What types of nickel alloys are out there？
The most widely welded nickel alloy is the pure nickel 200 and nickel 201. They are both corrosion-resistant, but nickel 201 has better resistance to carbon precipitation when used at temperatures higher than 315°C (600°F).
The nickel-chromium 600 alloy, also known as INCONEL alloy 600, is widely used for its corrosion resistance and high strength at increased temperatures. This alloy is often used in cryogenic service too, thanks to its excellent service temperature range from cryogenic temperatures to 2000°F. You'll often see aircraft parts like turbine seals and air-frame components made from this nickel alloy.
2. How to preclean nickel alloys before welding？
Clean the oils and paints by using degreasing solvents and alkaline cleaners. Then, remove the surface oxides we discussed earlier using the carbide deburring tools because they are most likely to completely remove the oxides.
3. What are the filler metal selection for welding nickel alloys?
The table below describes the most commonly used bare electrode filler metals for welding nickel alloys:
|
Filler Metal Selection For Welding Nickel Alloys |
|||
|
Welded Alloy |
Filler Metal AWS Designation |
Additional Information |
|
|
Pure Nickel |
ERNi-1 |
Contains a certain amount of titanium to control porosity |
|
|
Nickel copper |
ERNiCu-7 |
Used for many nickel copper alloys |
|
|
ERNiCU-8 |
This filler metal age hardens with heat treatment |
||
|
Nickel chromium iron |
ERNiCr-3 |
Also works for surfacing steel and joining steel to stainless or nickel-based alloys |
|
|
ERNiCr-7 |
Excellent resistance to high temperature oxidation, sulfidation, and carburization |
||
|
ERNiCrFe-5 |
Provides excellent resistance to high welding stress cracking. Great for welding thick sections |
||
|
ERNiCrFeAl-1 |
Particularly resistant to metal dusting in petro-chemical applications |
||
|
Nickel chromium molybdenum |
ERNiCrMo-3 |
Recommended for operating temperatures from cryogenic to 1000°F (540°C) |
|
|
Nickel molybdenum |
ERNiMo-2 |
Also used to clad steel with nickel-molybdenum metal |
|
|
ERniMo-8 |
Used for welding steel with 9% nickel |
||
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