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)