You just hit the nail on the head kevin, It is the colored oxide layer on the metal that makes it hard. If you heat the material and quench in water, it absolutely does make it harder. I don't know that it actually makes the metal harder, but the oxide layer created by rapid cooling does put a hard coating on Ti. Also Ti work hardens oh so easily. Use a dull high speed steel drill, and you may as forget about finishing that hole unless you use a carbide drill. I don't know if this has anything to do with the heat treating of the material, but I do agree with the other cats in this thread that it does work. When Ti is welded, it must be kept in a stable atmosphere as you said earlier, until the metal cools to 800 degrees. It is possible to weld Ti tubing with just a steady flow of argon through the inside of the tubing, and just the gas coming from your tig torch on the outside. If no shielding gas is used you will lose your tensil strength and the malerial will break at the weld. Oh and one more thing and I'll stop rambling, Don't use coolant with chlorine in it. Pure chlorine will make Ti as brittle as glass. Good luck everyone.
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