Cadmium plated hardware used on Titanium parts... 10

[RoarkS]

Was just reading QQ-P-416 Cadmium Plating.
6.1.1.1.1 basically says that Cad plating should not be used on titanium parts, and cad plated parts should not be used in contact with titanium parts.

Apparently it's right up there with Hydrogen embrittlement... who knew.

Is it only an issue if the parts get hot? If so, how hot?

and how far could the Cad embrittle the Ti part? could it cause a crack nearly an inch away from where a Cad plated fastener was used?

 

[RoarkS]

Also are we just talking commercially pure Ti, or would Ti alloys like Grade 5 Ti-6Al-4V be a bad choice also?

 

[GrandpaDave]

Suggestion: You should posed this same question under Materials Engineering. As an old stress guy, I would always coordinate with M&P (Materials and Processing) folks who are the experts. --- Grandpa Dave

 

[TVP]

Titanium is embrittled by cadmium from room temperature (solid Cd) up to the 320 C (molten Cd). This includes alloys such as Ti-6Al-4V, Ti-13V-11Cr-3Al, and Ti-8Al-1Mo-1V, not just CP Ti. The Cd must be smeared or pressed into highly stressed Ti surface such that the passive TiO[sub]2[/sub] film is compromised. References include the following:

"Stress Corrosion Cracking of Titanium Alloys" by R.W. Schutz, pages 265-297 in Stress Corrosion Cracking edited by R.H. Jones (ASM International, 1992)

"Solid Cadmium Embrittlement: Titanium Alloys", p 409 in Corrosion vol 236, no. 10, Oct 1970 by D.N. Fager and W.F. Spurr

"Solid Cadmium Cracking of Titanium Alloys", p 192 in Corrosion vol 20, no. 5, May 1973 by D.A. Meyn

 

[cloa]

http://mechanicsupport.blogspot.jp/2011/03/titanium-aircraft-limitations-in-usage.html

Cadmium concern and all the other aspects to be cautious of.

 

[WKTaylor]

Cadmium and silver are embrittling to titanium

REF MIL-HDBK-1568 MATERIAL AND PROCESSES FOR CORROSION PREVENTION AND CONTROL IN AEROSPACE WEAPONS SYSTEMS

5.4.3.4.3 Special precautions.
Titanium parts shall not be cadmium or silver plated. Cadmium plated clamps, tools, fixtures, and jigs shall not be used for fabrication or assembly of titanium components or structures.

5.4.3.2.1 Limitation on use of protective metallic coatings.
... Cadmium shall not be used on functional fuel systems components that can come into contact with fuel during operation of the aircraft. Cadmium plated fasteners, used in areas where contact with fuel can occur, shall be overcoated with an approved fuel tank sealant and coating over the sealant...

Cadmium exposed to fuel must also be avoided by overcoating parts with sealant. Cadmium dissolves [ion-by-ion] eventually leaving bare steel which can rust; and even small PPM of cadmium ions passing thru aircraft engines, via fuel, can cause damage.

Cadmium above 425F [to its meling point] becomes increasingly embrittling to steel [carbon and alloy]. The higher the strength state of the steel, the worse the effects.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[mfgenggear]

Wil that's important stuff, thanks for sharing.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[RoarkS]

THANKS ALL! My company uses Cd plated hardware extensively and have quite a few Ti-6Al-4V cast parts. Thankfully the 1 thing that would be a serious offender is out of production.

 

[WKTaylor]

In the mid-1990s, I was walking thru a USAF F-100-100 [P&W] [F-15C/D] engine shop, when I encountered a working-stock bin of [obviously] cad-plated monel blind rivets. I asked what they were used for and was told They secured a small tab on a titanium arm in the hot exterior of the augnmentor, among other things. I just about came unglued... no cad plated parts shouls be used for any turbine engine application!

The shop guys told me that cad-plated monel rivets were being substiuted by Defense Logoistics Agency [DLA] for bare monel rivets. When I called the F-100-100 and P&W guys they also went crazy: found out someone at DLA thought this was an excellent opportunity for minimizing stocklisted parts and saving $$s: use cad plated rivets for all applications structural, mechanical, etc! The USAF engine SPOs [system program offices] went thru an emergency purging of all working bins in back shops... and specified either bare or aluminum coated... but absolutely NO cadmium plated parts... in engine shops.

NOTE. IVD aluminum coatings would not harm any materials as best we/they could tell, up to ~1100F: and the organic-aluminum coated parts would probably burn-off aluminuminized organic binder part of the coating but still be relatively benign.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[TVP]

Wow, that's ridiculous, 20 years after it had been well-established that Cd embrittles titanium. And for hot-section parts of a military jet engine, no less...

 

[Screwman1]

Not surprising one bit that the DLA was involved. We asked about a Navy "Critical Safety Item" screw that was supposed to get 100% NDT and System 23 thread check; the contract was given for a piece price that was lower than just the NDT testing cost. The buyer told us, "just skip the NDT, nobody bothers to do that. Just put in your paperwork that the parts were NDT tested"!!!! Needless to say, we didn't get involved anymore with that buyer. The DLA is a scarey, scarey place if your are concerned about safety and quality.