Brazing is a joining process whereby a non-ferrous filler metal or alloy is heated to melting temperature above 450°C (842°F), or, by the traditional definition that has been used in the United States, above 800°F (425)°C and distributed between two or more close-fitting parts by capillary action. At its liquid temperature, the molten filler metal and flux interacts with a thin layer of the base metal, cooling to form an exceptionally strong, sealed joint due to grain structure interaction. With certain metals, such as Nitinol (Nickel Titanium) and Niobium, a low temperature eutectic can form. This leads to the bonding of the two metals at a point that can be substantially lower than their respective melting temperatures. The brazed joint becomes a sandwich of different layers, each metallurgically linked to the adjacent layers. Common brazements are about 1/3 as strong as the materials they join because the metals partially dissolve each other at the interface and usually the grain structure and joint alloy is uncontrolled. To create high-strength brazes, sometimes a brazement can be annealed, or cooled at a controlled rate, so that the joint's grain structure and alloying is controlled. It is also at 1/3 strength because the metal used to braze is usually weaker than the substrate metal because it melts at a lower temperature, ensuring the substrate does not melt.