How so? Grade five is always supplied in the annealed state and I have re-heated and either bent or beaten out dents many times. Unless you get it hot enough to cause hydrogen enbrittlement (IE welding temperatures) there shouldn't be a problem. I got my info from page 23 of this manual: http://www.timet.com/images/document...abrication.pdf

Notice that table 18 for cold forming recommends a bend radius of 9X the thickness for grade 5 thin sheet, while you can get down to 2X the thickness at 816 Deg. C. I try to get the titanium to a dull red and do the forming in several stages with a final heating to take out any work hardening.