Is welding titanium difficult? Both yes and no. Yes, because atmospheric contamination can very easily corrupt your weld. If you are yet to gain mastery over aluminum welding, working with titanium could be quite challenging for you.
But it is not as difficult to weld as some metallurgically complex metals and metal alloys like tungsten, copper-nickel alloy, zirconium, astatine, or osmium. The main prerequisite for titanium welding is that the process has to be performed in a contaminant-free environment.
Not sure how to start (or whether to) venture into titanium welding? In this beginner-friendly guide, I’m going to touch upon more or less everything related to titanium welding. Let’s jump in:
- Why Choose Titanium?
- What Are the Biggest Challenges of Welding Titanium and Its Alloys?
- Evaluating the Quality of Titanium Weld
- Preparing the Workstation for Titanium Welding
- Cleaning the Weld Surface and Filler Rod
- Choosing the Correct Filler Wire for Titanium
- Shielding Gas Coverage
- Recommended Welding Techniques for Titanium
- In Conclusion
Why Choose Titanium?
Titanium’s perfect strength-to-weight ratio opens up lots of possibilities for fabricators and welders. Twice as strong but almost half in weight, titanium is a highly sought-after metal for aerospace, marine, chemical processing, and military applications. Some other remarkable qualities of titanium include:
- Incredibly strong yet remarkably light, which is why it’s extensively used in industries like marine and aerospace for building structural frames.
- High melting point of 1668 °C.
- Superior ductility and formability at room temperature.
- Low thermal expansion.
- The oxide layer formed during the welding process shields the metal against corrosion. Titanium’s extremely low corrosion rates in chloride environments make it a go-to choice for chemical processing applications.
- Can easily handle temperatures up to 600° F without losing strength.
What Are the Biggest Challenges of Welding Titanium and Its Alloys?
Ambient air (oxygen and nitrogen) is a huge threat to the strength and purity of titanium welds. Titanium is a low-ductility, highly reactive material which starts to react with oxygen at 600 degrees F and with nitrogen at 800 degrees F.
The welder needs to take special measures to prevent the base metal from being exposed to oxygen, moisture, dirt, and grease at higher temperatures.
Moreover, a low stress-to-strain ratio makes titanium prone to deform quickly under tensile load. You need to choose the appropriate filler material to counter this problem.
Thankfully, technology has come a long way. Earlier, titanium welding was only performed in purged gas chambers. Even though it’s the most foolproof way to prevent contamination, it can be quite expensive.
Today, a skilled titanium welder can carry out the task in open-air environments by means of back purging and backup shielding. It’s still an extremely high-skilled job. It requires the welder to possess excellent hand-eye coordination so as not to rip the protective inert gas barrier while welding.
Evaluating the Quality of Titanium Weld
Weld discoloration is the inevitable result of contamination.
A bright silver color is a tell-tale sign of a good weld. But anything between straw to light gold is also acceptable. However, anything beyond that is an indication of metal contamination.
A light blue tint is salvageable as it’s caused by surface oxide. Remove it with a stainless steel wire brush and you are good to go.
However, dark blue, green, grey, and white-colored welds are acceptable as they indicate surface contamination. In such cases, you need to take a step back, find the root of the problem and eliminate it before you proceed any further.
Preparing the Workstation for Titanium Welding
The key to quality titanium welds is cleanliness. Dirt, grease, moisture, air drafts, paint, and other contaminants can wreck the corrosion resistance of the base metal and cause brittleness. Despite the staggering operational cost, sealed chamber welding is still a norm for small-scale, intricate projects.
However, for large-scale industrial projects, open-air welding is a standard practice in most fabrication shops.
Set aside a separate workstation, away from your regular workstation where dust-causing applications like grinding and painting take place. Pay a great deal of attention to humidity control as moisture can corrupt the weld very easily.
For a sparkling clean work environment, I would recommend steam cleaning the area followed by deep cleaning with diluted sodium hydroxide or any non-chlorinated chemical cleaner.
You would want to avoid moisture at all costs. So either let the surface air dry for a couple of hours or use a hot air blower to save time. If you’re going to use a hot air blower, double-check your chemical cleaner to make sure it’s not flammable.
Cleaning the Weld Surface and Filler Rod
Our hands are a warehouse of dirt, body oils, germs, and whatnot! That’s why it’s crucial to thoroughly clean the base metal as well as all the welding equipment to prevent contamination.
Use non-chlorinated chemical solvents like methyl ethyl ketone (MEK) or acetone and a lint-free cloth or sponge to wipe off the joints and surrounding areas.
Make sure to cover your hands with nitrile gloves while handling the weld pieces and equipment. Avoid rubber gloves as they may also contain chlorine.
Follow it up by wire brushing the oxide layer off the surface. In room temperature, titanium reacts with oxygen which forms a protective layer of titanium dioxide on its surface.
The problem with oxide films is that it has a much higher melting point than the base metal. I’d recommend using a stainless steel wire brush to remove the film from both the inside, outside, as well as the edges of the surface. Light grinding or filing the surface works too.
Finish off by giving it another round of cleaning with acetone or MEK, just to be safe.
Note that you might notice oxide formation on the surface at temperatures around 600-800 degrees F. Use a new stainless steel wire or slowly grind them off as you go. In some cases, you may have to dip the weld joint in a pickle bath of 35 vol.% nitric and 5 vol.% hydrofluoric acids.
Don’t forget to clean the filler rod as well while you are at it. Give it a good wipe with acetone or whichever solvent you have been using for the metal.
For the sake of optimum purity of the weld, store the filler rod in an air-tight container after cleaning. Take it out right before you start welding the clean titanium. Also, when not welding, cover the weld joints with plastic or a piece of paper to minimize contamination.
Choosing the Correct Filler Wire for Titanium
As a general rule of thumb, you should factor in the properties and composition of the base metal while choosing the filler wire. Ideally, the filler material should have the same properties as the base metal for optimal joint ductility.
However, when working with commercially pure high strength titanium, I’d choose a wire that’s one grade below the strength level of the base metal. Certain applications may also require the welder to select a different category of filler material.
2% Ceriated Tungsten electrode is my go-to choice for welding aluminum. For welding at 125-200 amps, choose a rod diameter between 1/16-3/32”. For anything above 200 amps, the diameter should be between 3/32” to ⅛”.
Tubes and pipes thinner than 5 mm should be welded autogenously (without any filler material) to minimize heat input. That said, in some cases, AWS D10.6 recommends using v-groove on thickness above 2.4mm.
Shielding Gas Coverage
Having the right inert gas shielding and proper coverage will keep your weld from getting corrupted by ambient impurities and also keep the temperature in check.
Select the purity and dew point level based on your welding applications. Most welders, including me, would recommend 100% pure argon gas with a dew point less than -50°F for your primary shielding. Certain applications may also call for 99.999% purity.
Even a slight impurity could lead to mottling or blue/yellow tinting.
Helium could be a substitute for argon for backup shielding. I would still suggest you stick to argon due to its high density which promotes better arc stability.
The use of 75/25 or 70/30 argon/helium mix as shielding gas for titanium welding is uncommon.
For fail-safe coverage, you need separate gas supplies for the following steps:
The purpose of primary shielding is to protect the molten weld puddle from reacting with oxygen and other foreign substances. Your first task is to select a welding torch.
The standard water-cooled torch with ¾ -1” ceramic cups and gas lenses is best-suited for titanium welding. Make sure to choose wide cups for full coverage of the molten pool while the gas lenses aid steady gas flow.
The purpose of secondary shielding is to keep the weld pool and heat-affected zones from exceeding the 600-800F threshold. Failing to cool down the metal at this point would result in the loss of corrosion resistance and material degradation.
You will need trailing shields for this which you can either purchase or custom-fabricate for your welding torch and the kind of joint configuration you’re aiming for.
The trailing shield needs to be compact to ensure a uniform and uninterrupted flow of inert gas within the device. You may require water-cooling for large shields. I recommend porous copper purge blocks as they facilitate a uniform distribution of gas.
The function of backup shielding is to provide gas coverage to the backside and surrounding heat-affected zones of the weld pieces. These devices can be either handheld or clamped into position. Additionally, you can fashion water-cooled grooved copper bars into heat sinks to cool down your weld.
Important note: The presence of air in primary, secondary, backup shielding equipment can ruin your weld. Therefore, it’s absolutely necessary to back purge the tubes and pipes with inert gas.
Selecting the Right Equipment
For welding titanium tubes and pipes, choose a low amperage welder with DC capabilities, preferably 3-200 amps. HF (high-frequency ignition) and pulse capabilities will also provide an added advantage.
Tips for Joint Prep
A tight joint fit-up is extremely crucial to the success of titanium welding. Poor fit-up not only increases the risk of contamination but also makes your base metal susceptible to burn through. Use clamps to avoid joint movement while welding.
If you are using tack welds, exercise proper maintenance by cleaning the surface with non-chlorinated chemical solvents. Don’t forget the insert gas shielding to keep contamination completely out of the way.
Next, carefully select a joint design that allows inert gas coverage and a thorough post-weld inspection on both the face and root sides of your weld.
The joint surface throughout the entire process must be oxide-free and smooth. Use a sharp file to smooth out the burn marks and sharp edges developed during grinding.
Recommended Welding Techniques for Titanium
Tungsten Inert Gas (TIG)/Gas Tungsten Arc Welding (GTAW)
This process uses a non-consumable electrode and is a popular method for joining titanium and its alloys. You can also weld without filler material if the base metal is less than 2.5mm in thickness.
Metal Inert Gas (MIG)/Gas Metal Arc (GMA)
For beginner to intermediate-level welders, MIG might be a safer option for pieces over 3 mm in thickness. TIG welding has very little room for mistakes. If the welder doesn’t know exactly what he is doing, it could result in a burn-through or serious defects in the weld.
Electron Beam Welding (EBW)
Electron beam welding is a standard choice for reactive metals like titanium as it takes place in a vacuum. The beams are capable of generating intense heat which leads to extremely strong and durable joints.
That’s one of the main reasons why electron beam welding is extensively used in aviation, aerospace, and marine industries.
Resistance Welding (RW)
In resistance welding, a precisely controlled amount of current is passed to the plates for a short period. This reduces heat zones and thus minimizes the risk of burn-through. RW spot or seam welding is standard for joining titanium to stainless and carbon steel.
A few other standard welding techniques for titanium include:
- Laser Beam Welding (LBW).
- Friction Welding (FW).
- Plasma Arc Welding (PAW).
As you have learned by now, ambient air, grease, dirt, and moisture are like kryptonite to titanium. The key to getting consistent and quality titanium welds is to prevent contamination and overheating every step of the way. How you finish the welding is just as important as weld preparation.
A careful post-weld inspection for discoloration or cracks will help you determine the quality of your weld. That’s all for today. Hope this guide helped you gain a good grasp of the basics of titanium welding.