• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • There is no better time to show your support for SuperCub.Org than during our annual calendar campaign! All the details are HERE

Ti gear install hardware

redfin

FRIEND
Can anyone fill me in on what hardware is compatible with Ti gear?

I have been told that Cadmium plated hardware will become ‘brittle’ when in contact with Ti. Does anyone have any experience here or know if this is true?
 
Engineering food for thought.

https://mechanicsupport.blogspot.com/2011/03/titanium-aircraft-limitations-in-usage.html
https://www.eng-tips.com/viewthread.cfm?qid=332583

Cadmium Plate Caution

Cadmium plated self-locking nuts shall not be used in contact with titanium and titanium alloy bolts, screws, or studs in application where the operating temperature exceed 450 degrees F. Cadmium plated clamps, fixtures, and structures per Aeronautical-Design-Standard-ADS-13F-HDBK. Note, when considering localized cadmium embrittlement of titanium, consider that friction can sometimes cause this heating effect.

Boeing-Design-Manual-BDM-1054 states "The use of cadmium plated titanium components is not allowed. Cadmium plated components which come in contact with titanium are not allowed, except for hydraulic systems where cadmium plated steel fittings may be coupled to titanium fittings and cadmium plated steel or titanium nuts on titanium or steel bolts.

MIL-S-5002 prohibits all contact between titanium and cadmium on military programs." Cadmium plated clamps, fixtures, and\ jigs should not be used for the fabrication or assembly of titanium components or structures.

Cadmium plated self-locking nuts shall not be used in contact with titanium and titanium alloy bolts, screws or studs. MIL-HDBK-1599A.
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.

"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

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 TiO2 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)
 
The Titanium becomes brittle, not the hardware. I assume its measurable at all temperatures but most apparent at higher ones.

If concerned for your application use a 431 stainless steel bolt ANx(C)-x bolt instead of 8740 cad plated alloy steel. They have the same 125KPSI designation. Aircraft spruce carries them just add the (C) after the length digit.

Hope that helps.

-Chet
 
Engineering food for thought.

https://mechanicsupport.blogspot.com/2011/03/titanium-aircraft-limitations-in-usage.html
https://www.eng-tips.com/viewthread.cfm?qid=332583

Cadmium Plate Caution

Cadmium plated self-locking nuts shall not be used in contact with titanium and titanium alloy bolts, screws, or studs in application where the operating temperature exceed 450 degrees F. Cadmium plated clamps, fixtures, and structures per Aeronautical-Design-Standard-ADS-13F-HDBK. Note, when considering localized cadmium embrittlement of titanium, consider that friction can sometimes cause this heating effect.

Boeing-Design-Manual-BDM-1054 states "The use of cadmium plated titanium components is not allowed. Cadmium plated components which come in contact with titanium are not allowed, except for hydraulic systems where cadmium plated steel fittings may be coupled to titanium fittings and cadmium plated steel or titanium nuts on titanium or steel bolts.

MIL-S-5002 prohibits all contact between titanium and cadmium on military programs." Cadmium plated clamps, fixtures, and\ jigs should not be used for the fabrication or assembly of titanium components or structures.

Cadmium plated self-locking nuts shall not be used in contact with titanium and titanium alloy bolts, screws or studs. MIL-HDBK-1599A.
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.

"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

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 TiO2 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)
 
My name is Doug Keller, I am the Principal R&D Engineer at Alaska Gear Company. We have taken a deep look into using CAD plated hardware to fasten titanium alloys parts. The FAA did initially question us about this during the certification process of our titanium landing gear. I explained to the FAA that they had already approved similar examples of products using CAD plated fasteners with titanium alloy. Here are a couple of examples right in our back yard:

  1. Burl’s AOSS uses a titanium end fitting that is bolted onto the gear leg using CAD plated bolts. Our TiSHK suspension’s end fitting is an exact copy of Burl’s AOSS end fitting.
  2. The Landing Gear Group bolts their titanium 180/185 gear legs onto the fuselage using standard CAD plated AN hardware.
There are other examples, these are just a few that are likely familiar to everyone. Once I showed these examples to the FAA, they retracted their concern.

I also did some other research to get a better understanding of the issue. This is a quote out of the ADS-13F-HDBK 16, June 1997, Aeronautical Design Standard Handbook Air Vehicle Materials and Processes

“7.12.5 Special plated part considerations. Cadmium- and silver-plated parts and fasteners should not be used in contact with titanium components if use temperatures are expected to exceed 230°C (450°F).”

I also purchased a technical paper “Corrosion of Titanium and Titanium Alloys” for research purposes. According to the author:

“The cadmium must be smeared or pressed (beyond the yield point) into the highly stressed titanium alloy surface at loads exceeding the yield stress for the brittle failure to occur. Simply stressing cadmium-coated titanium is not sufficient to initiate cracking. Increasing temperature and stress level decrease time to cracking and increase crack depth. Any barrier film or coating that inhibits direct bearing contact of cadmium onto titanium alloy surfaces can avert cadmium embrittlement. For example, sprayed vapor-deposited aluminum coatings, organic coatings, dry film lubricants, and/or oxidized surfaces on titanium may provide effective protection, depending on bearing loads”

The bottom line is that the joint needs to be at elevated temperatures and highly stressed for pro-longed durations for this to be a concern. We operate at very low temperatures and our fittings are not stresses beyond yielding and when stressed it is very infrequently. Our products spend 99.9% of their time in the resting static position (very low loading).

Any mechanic installing landing gear assemblies that rotate will apply grease to the attaching hardware to reduce friction and prevent corrosion. We suggest that during installation, the installer apply a liberal amount of grease to the mounting hardware at assembly. Hopefully this will help explain our position on this and why we are not concerned.
 
Back
Top