Hydrogen Embrittlement of Titanium

Exactly, hydrogen is the classic issue with titanium. It diffuses into the heat-affected zone and forms hard, brittle hydrides there. That becomes glassy and breaks off under load later, often only after hours or days. Therefore: flood the weld zone and the cooling material with shielding gas until it is really cold. Everything that comes into contact with the hot area must be absolutely free of grease and moisture – including the wire. If you are sloppy there, you will get fine cracks that you only see when it's too late.