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I'm aware that polymers like most plastics can go through stress cycles indefinitely as long as the covalent bonds are not ruptured.

On the other hand, I hear that even metals like steel and titanium do have limited life-spans no matter how small the stresses.

I'm quite interested in the application of diamond-like carbon coatings to materials. Some of these coatings can even be flexible. For example, I'm beginning to see DLC being applied to headphone diaphragms, which have to be a little flexible.

So while the plastic diaphragm that the DLC is bonded to may have an indefinite service life, I'm not sure if the same is true for the DLC coating itself. Would anyone be able to give me an insight into whether or not a DLC coating would have an indefinite life like polymers, or if it has a certain amount of cycles it can go through before it starts to deteriorate?

Anthropologist
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  • All materials suffer from fatigue or creep or some form of breakdown eventually. No material has an indefinite lifespan. – DrMrstheMonarch Dec 11 '19 at 10:28
  • Steel/iron is an ( the) exception. With maximum stress below half of tensile strength, steel has infinite life. I expect the fatigue life of a coating would depend on the substrate life, at best. – blacksmith37 Dec 11 '19 at 15:18
  • @blacksmith37 Don't polymers have the same fatigue qualities? The thing is a DLC coating isn't quite a metal or a polymer, so I'm not sure what sort of qualities it would have. – Anthropologist Dec 12 '19 at 01:58
  • @blacksmith37 the theoretical fatigue limit is certainly a research factor. However a (very) high cycle rate is certainly not an *infinite* one. – DrMrstheMonarch Dec 12 '19 at 12:09
  • How about " a very long undefined life time ; the end of which is not realized in properly designed steel components". – blacksmith37 Dec 13 '19 at 14:54

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