Cad plated bolting - temp limits 1

[nickt1960]

I would like to know why many specs call for not using cad plated bolting in applications above 200 degrees C. Is it an HSE issue or a coating integrity issue? I am referring to A320 L7 bolts.

 

[ijzer]

This is probably due to the danger for LME (liquid metal embrittlement)

 

[CoryPad]

Cadmium melts at 320 &[ignore]deg[/ignore];C. The max use temperature for fasteners and other highly stressed parts is kept significantly below this (as you know, specifications list ~ 200 &[ignore]deg[/ignore];C) to prevent degradation of the coating and fastener. Liquid Metal Embrittlement would be a worst-case scenario.

 

[kenvlach]

This is due to Solid Metal Induced Embrittlement (SMEI or SME). See ASM Handbook Vol. 13 Corrosion, pp. 184-187 (1987) or Physical Metallurgy Handbook, A. K. Sinha, pp. 14.106-14.108, McGraw-Hill (2003).

It appears that SME has only been observed for those metal combinations in which LME can occur. Prerequisite for SME failure are a) the presence of tensile stress (either residual or applied) and b) a crack initiation site (even a grain boundary) at the embrittler/substrate interface.

For Cd on high strength steel, most examples of delayed failure due to SME were for temperatures of 188^oC or above. One sturdy for Cd/4340M reported failure at 38^oC, M. Hasegawa and S. Nomura, JISI, Japan, vol. 7, p. 187 (1977).