A question on the Ti - if it gets stronger with heat does it act like

6064

Al whereby the Al gets harder as it is artificially ages with heat, or

is it

a cyclic thing and if cyclic (ie hard then soft), would that induce

cracking

at welds etc.

George (down under)

George, The Ti doesn't cycle harden. The most likely cause of cracks 
is the welding process itself. The material does change color as Ed K 
mentioned, The headers do turn blue like a chrome pipe that was overheated. 
Ti is very unusual in that the tensile increases for about the first 700°F 
Then goes down again. There are many Ti alloys the correct one would need to 
be selected. Ti is stronger than aluminum to begin with by about 1/3, 
(close to steel). Ti will alloy with almost anything metal, (which is 
very unusual) so it needs to be kept away from some that can make it
 brittle like chrome. The fasteners in the early SR 71's kept breaking 
until someone discovered that chromium from the tools was effecting 
the Ti. Bill Jepson

 
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