I don't think ti is a very expensive metal. My wedding ring cost £30. Hardly dear compared to other metals you could use for a ring.
I think its expensive because its h ard to weld properly.. I think it reacts to oxygen and then you get a discolouring around the weld. You need inert gas to purge the area local to the weld of o2 then or weld in a sealed box with no air in it, in an inert gaseous atmosphere.
IT will come as no surprise to fabricators with experience in handling titanium that special consideration needs to be taken during preparation and welding.
Titanium and its alloys are reactive and can become contaminated by atmosphere gases. Adequate shielding using inert gas is essential if repeatable, high- quality joints are to be made.
For many years it was believed that welding-titanium could only be performed satisfactorily in sealed chambers equipped with glove ports and viewing ports and filled with high-purity, inert gas such as argon.
A better understanding of the mechanism of metal/gas interaction has shown that for some applications, as long as adequate local shielding is maintained during welding, the use of sealed chambers with or without vacuum pumping systems may not be absolutely necessary.
This understanding has afforded possibilities for welding large titanium fabrications and significantly extended the application areas for the metal and its alloys into major structural forms, especially in the aerospace industry, the motor sport industry and latterly in the petrochemical industry. The primary requirement then is to provide a protective gas atmosphere to the joint area during welding and subsequent cooling.
The weld purge gas must be used correctly. It should be 99.999% pure, even 99.995% gas can lead to some yellow discoloration.
If the colour of the welded metal begins to mottle, or if it exhibits any hint of blue, the gas isn’t pure enough, or it isn’t being applied correctly. The gas flow should be started several seconds before starting to weld. If there is enough shielding and the argon is being dispersed evenly over the part, a uniform colour will be seen.
Protective gas flow is still needed after welding until the metal has cooled below about 250°C to prevent discolouration.