i have experience with using grade 5 ti as armor for a battlebot. it's a pain in the a** to drill with a cordless drill, throws awesome sparks when you cut it with a cutoff disk, cuts nicely with a good bandsaw, pain to weld because it sometimes warps and is near impossible to bend unless you heat it up. oh and it's really expensive. but it's tough as anything.
best place to buy it is
titanium joe