Superalloys are nickel, cobalt or iron based alloys with high contents of tungsten, molybdenum, tantalum and, more recently, also rhenium. Sixteen or more elements can be contained. Their important properties are: high-temperature strength, high creep strength at high temperature, high thermal fatigue resistance, good oxidation resistance, excellent hot corrosion resistance, air melting capability, air or argon remelting capability, good welding properties and ease of casting. Tungsten accounts for solid solution strengthening, strengthening by formation of intermetallic compounds (eg Co3W), and formation of carbides. Superalloys are used in aircraft engines, marine vehicles, and stationary power units as turbine blades and vanes, exhaust gas assemblies and burner liners. They are also used as construction material for furnace parts.