Materion sells 4 types of amorphous metal alloys,it cost huge amount of money,1000 dollar per kilogram.My question is,why would anybody choose it over lets say titanium 6al-4v?
I assume you're talking about their bulk metallic glass (BMG), aka amorphous glass forming alloys.
To quote their site:
HIGH PERFORMANCE ALTERNATIVE TO TITANIUM
BMGs have strength-to-weight ratios more than twice those of titanium, magnesium and aluminum alloys. Amorphous alloys typically have elastic limits that can be three times higher than crystalline metallic alloys and exhibit outstanding corrosion resistance due to their unique atomic structure and composition.
EASY TO FABRICATE
These amorphous alloys have the additional benefit of near net shape fabrication by injection molding and by a thermoplastic forming process, similar to plastics.
Whether or not that's worth the extra cost depends on your circumstance.