Titanium (Ti)

Titanium readily picks up carbon and nitrogen from the environment. If you don't control that when welding, you'll get porosity in the weld metal and the structure becomes brittle. But this bonding to these elements is also what keeps the grain fine and improves mechanical properties. So make sure the melt is clean and well shielded so nothing gets in from outside. With proper deoxidation and controlled heat input, you stay on the safe side and avoid cracks and loss of strength.