Single crystal (SC or SX) alloys, are a mixture of metals that are cast into one continuous crystal. Forming single-crystal metal objects requires both special alloys and special casting techniques. The alloys are almost always nickel-based, with as many as nine minor metal components including five or more per cent chromium, cobalt, tungsten, tantalum, aluminium, and/or rhenium. The casting method is known as Dzdirectional solidification, dz and involves carefully cooling a cast metal part starting at one end to guarantee an orientation of its crystal structure. That orientation is chosen, naturally, based on expected stresses in the finished part. The primary application for single crystal super alloys is the manufacture of jet engine turbine blades, which must endure tremendous forces at extremely high temperatures for prolonged periods of time. Under such conditions, metals with a grain structure tend to Dzcreep,dz or slowly deform, along grain boundaries. Because single-crystal alloy parts have no grain boundaries, however, they are highly resistant to this kind of wear. This allows jet engines to have better performance for longer.