Galvanic corrosion and the Ti frame?

[Zak Smith]

I am strongly considering having a Ti-framed Commander-sized 1911 built for the purpose of lawful CCW and "shooting a lot." Titanium seems like a good choice for this because of its light weight vs. steel and strength vs. aluminum. By my calculations, a loaded Ti-Commander would weigh in at about 35oz, while the BHP I currently carry should be about 39oz, loaded.

I have read here and elsewhere about "galvanic corrosion" - that is, when two dissimilar metals are used, corrosion on the less noble material is accelerated. When saltwater (e.g. sweat) is present, the corrosion rate of the anodic material is accelerated proportional to the exposed cathodic area and the potential difference.

From:
http://www.corrosion-doctors.org/Aircraft/galvdefi.htm

Galvanic corrosion (also called ' dissimilar metal corrosion' or wrongly 'electrolysis') refers to corrosion damage induced when two dissimilar materials are coupled in a corrosive electrolyte. It occurs when two (or more) dissimilar metals are brought into electrical contact under water. When a galvanic couple forms, one of the metals in the couple becomes the anode and corrodes faster than it would all by itself, while the other becomes the cathode and corrodes slower than it would alone. Either (or both) metal in the couple may or may not corrode by itself (themselves) in seawater. When contact with a dissimilar metal is made, however, the self corrosion rates will change:

(1) corrosion of the anode will accelerate
(2) corrosion of the cathode will decelerate or even stop.

The driving force for corrosion is a potential difference between the different materials. The bimetallic driving force was discovered in the late part of the eighteenth century by Luigi Galvani in a series of experiments with the exposed muscles and nerves of a frog that contracted when connected to a bimetallic conductor. The principle was later put into a practical application by Alessandro Volta who built,
in 1800, the first electrical cell, or battery: a series of metal disks of two kinds, separated by cardboard disks soaked with acid or salt solutions. This is the basis of all modern wet-cell batteries, and it was a tremendously important scientific discovery, because it was the first method found for the generation of a sustained electrical current.

The principle was also engineered into the useful protection of metallic structures by Sir Humphry Davy and Michael Faraday in the early part of the nineteenth century. The sacrificial corrosion of one metal such as zinc, magnesium or aluminum is a widespread method of cathodically protecting metallic structures.

In a bimetallic couple, the less noble material will become the anode of this corrosion cell and tend to corrode at an accelerated rate, compared with the uncoupled condition. The more noble material will act as the cathode in the corrosion cell. Galvanic corrosion can be one of the most common forms of corrosion as well as one of the most destructive.

In the case of titanium, steel, and aluminum, both aluminum and steel are relatively very active (anodic) and titanium is much more noble (less active, cathodic). [ http://www.corrosion-doctors.org/Aircraft/galvseri-table.htm ] For example, the potential of Al and steel is in the range of -0.6 to -0.8V. Titanium is in the range of -0.05 to 0.06. [ http://www.ocean.udel.edu/mas/masnotes/corrosion.html ]

What does this mean for building a pistol with a titanium frame?

Sure, titanium is great because it does not corrode, but (ironically) it may accelerate corrosion of the steel and aluminum parts in the pistol.

I would think that if one had, for example, a steel MSH and a titanium frame, and that area was bathed in sweat, the steel part would corrode faster than normal.

To what extent does this problem manifest in titanium-framed pistols?

Has it affected how Ti-framed pistols are built? Have any of the ti-framed pistols out there had any problems with galvanic corrosion?

Does coating the titanium frame with something like Black-T or
hard-chrome help?

I would appreciate if an expert in the area would comment on these issues, since we aren't used to thinking of a pistol as a battery!

thanks
Zak

 

[HSMITH]

Hard chrome it and forget about it.

 

[dude]

FWIW-- most all aircraft grade titanium made parts/interior skins are left unpainted with no chemical coatings at all (737NG flap tracks for example) and they are subject to lots of water/salt, temperature extremes and various other metals. They are only painted to match exterior paint schemes if they are at the airframe skin.

You will never have to worry about corrosion problems with your ti frame, enjoy!

 

[Zak Smith]

dude,

most all aircraft grade titanium made parts/interior skins are left unpainted with no chemical coatings at all (737NG flap tracks for example) and they are subject to lots of water/salt, temperature extremes and various other metals

Since titanium would be the less reactive and more cathodic material in the galvanic circuit, it would be the steel or aluminum that would corrode when combined with titanium, right?

The concern wouldn't be about corrosion of the titanium frame, but of the steel and aluminum parts in the gun - such as the tool-steel lockwork and aluminum MSH - would corrode.

thanks
Zak

 

[Handy]

Galvonic corrosion generally only occurs when dissimilar metals are pressed together, not just touching. The gun oil would prevent most parts from reacting at all.

The only parts I would wonder about would be the grip screw bushing or safety spring plunger. I would still doubt that it would be much of a problem with all the oil present, but locktite should shield the parts from direct interaction.

I have never seen parts screwed into unfinished Ti bicycle frames corrode. Either it doesn't happen easily, or a little grease/locktite/oil works wonders.

 

[dude]

the bike example is spot-on

Ti, while an anode is still very inert and does not cause the corrosion trouble you are worried about. That's why it's so cool! (and expensive @ over $90/lb scrap)

 

[mete]

It isn't a problem. You are going to lube it anyway and that will block the galvanic process. Ti on its own is one of the most corrosion resistant metals. It's about the only thing that you can use for a desalinization plants that will last forever.