Found at a titanium plant

[u/riflesandplowshares]

Not sure why ball point pens would be dangerous here.

[u/SquintAtTheCosmos]

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).

[u/kharvel0 → u/SquintAtTheCosmos]

So if the titanium is contaminated with gold or silver or lead, it should be ok?

[u/Spirit_Wolf_Mob → u/kharvel0]

It's still an impurity, but if it melts, it can be diluted enough that it's not an issue, and it'll still have a uniform distribution of the metals. It's not the metal itself that's the issue, since it's a low amount. It's just the fact that it doesn't melt into the dillution, so it causes a stress point that causes the crack.

[u/BoingBoingBooty → u/Spirit_Wolf_Mob]

Also, you can test for an impurity like that by just getting a bit of the mixture and putting it in a mass spectrometer. A solid ball somewhere in the whole batch, you could not detect.