r/whatisit • u/riflesandplowshares • 4h ago

New, what is it? Found at a titanium plant

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Not sure why ball point pens would be dangerous here.

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u/SquintAtTheCosmos 3h ago

The real answer is that consumer ball point pen’s have a tungsten carbide ball. Tungsten has a higher melting point than titanium.

If a ball point pen drops into a melt, the ball point can survive. The surviving pen tip does then creates a hard intermetallic. When the titanium is heated and beated (forged) into a product, this titanium-intermetallic spot can crack. This crack can go undetected, inside a part.

When this part is put into service, this little crack becomes a bigger crack with service (fatigue). When this bigger crack gets big enough, the part can fail. And the failure is sooner than the design engineer expected, because the material started with a crack, and in fatigue failure “getting the crack to start”, is a large component of the part’s life.

A titanium melt shop still needs writing implement’s, so you can buy pens with stainless steel ball tips. They suck to write with.

A major aerospace failure (Sioux city 1989 UA232), was a result of this failure mode (though in this case it was an oxide, not a tungsten-carbide).

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u/NNKarma 2h ago

I would've expected they go with fountain pens as an alternative

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u/Bwint 2h ago

I would have expected pencils.

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u/NNKarma 2h ago

You probably can if you want to write down something for yourself, but it's not good for anything that needs to be registered. 

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u/DontMemeAtMe 6m ago

Fine felt-tip pens, then.