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Boriding
Boriding, also called boronizing, is the process by which boron is introduced to a metal or alloy. It is a type of surface hardening. In this process boron atoms are diffused into the surface of a metal component. The resulting surface contains metal borides, such as iron borides, nickel borides, and cobalt borides, As pure materials, these borides have extremely high hardness and wear resistance. Their favorable properties are manifested even when they are a small fraction of the bulk solid.〔Helmut Kunst, Brigitte Haase, James C. Malloy, Klaus Wittel, Montia C. Nestler, Andrew R. Nicoll, Ulrich Erning and Gerhard Rauscher "Metals, Surface Treatment" in Ullmann's Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. 〕 Boronized metal parts are extremely wear resistant and will often last two to five times longer than components treated with conventional heat treatments such as hardening, carburizing, nitriding, nitrocarburizing or induction hardening. Most borided steel surfaces will have iron boride layer hardnesses ranging from 1200-1600 HV. Nickel-based superalloys such as Inconel and Hastalloys will typically have nickel boride layer hardnesses of 1700-2300 HV.
== Methods ==
Boriding can be achieved in several ways, but commonly the metal piece is packed with a boriding mixture and heated ca. 900 °C. Typical boriding mixture consists of boron carbide powder diluted with other refractory materials such as alumina or silicon carbide. Potassium tetrafluoroborate (KBF4) is used as a flux. The process converts some of the Fe to iron boride, consisting of two phases: FeB concentrated near the surface, and diiron boride (Fe2B).〔 Boride layer depths can range from 0.001 - 0.015 inch depending on base material selection and treatment.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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