from wiki:
Small amounts of yttrium (0.1 to 0.2%) have been used to reduce the grain sizes of chromium, molybdenum, titanium, and zirconium.[81] Yttrium is used to increase the strength of aluminium and magnesium alloys.[15] The addition of yttrium to alloys generally improves workability, adds resistance to high-temperature recrystallization, and significantly enhances resistance to high-temperature oxidation (see graphite nodule discussion below).[68]
Yttrium can be used to deoxidize vanadium and other non-ferrous metals.[15] Yttria stabilizes the cubic form of zirconia in jewelry.[82]
Yttrium has been studied as a nodulizer in ductile cast iron, forming the graphite into compact nodules instead of flakes to increase ductility and fatigue resistance.[15] Having a high melting point, yttrium oxide is used in some ceramic and glass to impart shock resistance and low thermal expansion properties.[15] Those same properties make such glass useful in camera lenses.[51]
