It is known that titanium resistance welding is sensitive to heat and exposure to air. Titanium expulsion can be very exciting if the process is not controlled.
AWS C1.1 “Recommended Practices for Resistance Welding” states that titanium can be resistance welded. The molten nugget is sealed away from air by the surrounding solid material. Shielding gases are not necessary.
AWS C1.1 offers some surface cleaning options and a table with weld schedule data for spot welding Titanium Ally 6%Al-4%V.
Reference: AWS C1.1, Recommended Practices for Resistance Welding
RWMA - Resistance Welding Manual 4th Edition