Funny things happen with metal

[Shannow]

Following on from the anti-sieze thread, I thought I'd post some of the strangeness that happens with metals, particularly in high temperature applications.

The anti-sieze thread mentions copper and stainless, where the copper migrates into the grain boundaries, weakens the metals, and allows cracking to start.

Industry wide, the problem has been caused by something apparently as innocuous as a paint marker...

The pigments in paint markers can include any range of low melting point metal oxides, which when brought up to temperature can attack the metals. Chlorides can induce stress corrosion cracking in stainlesses.

We need to get certified marker pens to mark stuff up, and the purists don't even trust those, and mark out repairs with ribbons.

Chlorides, and welds in stainless (well stainless in general) can cause stress corrosion cracking, even before the welds have cooled...a salt spray can doom a component in transport to an early failure. A single salt leak can result in a turbine blade lasting 11 years rather than 50.

Some neat youtube examples of some of these unusual phenomena at room temperature.

 

[SteveSRT8]

outrageous vids.

Thanks for the post.

 

[oldhp]

So if you got a all aluminum 427 Cobra....don't tick off the little nerd down the street.

 

[tom slick]

I'm guessing gallium and mercury are bad oil additives. Really interesting to watch.

When I worked on jets we had separate files (for blending nicks out of blades) for stainless steel and titanium. We had yearly corrosion control training and a big deal was made of using the correct materials. The wrong rivets used in a sheet metal structure, mixed with salt air or degreasers, could cause major failures.

 

[morris]

at Boeing we had a whole booklet on working with titanium. lead or graphite was to NOT touch titanium. and machining it had to be done only with flood coolant, for fire control. machined titanium seamed to have sharper edges than other metals, ie they cut your skin much faster.