Surface Engineering for Friction and Wear Reduction
Surface treatments have long been an important remedy for wear problems, and that importance has
grown in recent years with the introduction of new techniques to harden surfaces or apply hard surface
coatings. Available processes and characteristics for treating a steel substrate are listed in Table 3.10.2.
Thermal transformation hardening processes are used to harden ferrous (primarily steel) surfaces by
heating the surface rapidly, transforming it to austenite, and then quenching it to form martensite. The
source of heat can be one of the following: an oxyacetylene or oxypropane ?ame (?ame hardening),
eddy currents induced by a high-frequency electric ?eld (induction hardening), a beam from a highpower
laser (laser hardening), or a focused electron beam (electron beam hardening). The depth and
uniformity of the hard layer depend on the rate and method of heating. These processes are characterized
by a short process time and all except electron beam hardening (which requires a moderate vacuum)
can be done in air.
Thermal diffusion processes involve the diffusion of atoms into surfaces to create a hard layer. In the
most widely used of these processes, carburizing (or case hardening), carbon diffuses into a low-carbon
steel surface to produce a hard, carbon-rich case. The hardness and thickness of the case depend on the
temperature, exposure time, and source of carbon (either a hydrocarbon gas, a salt bath, or a packed bed
of carbon). Carbonitriding is a process similar to carburizing which involves the simultaneous diffusion
of carbon and nitrogen atoms into carbon steel surfaces. In the nitriding process, nitrogen atoms diffuse
into the surface of a steel which contains nitride-forming elements (such as Al, Cr, Mo, V, W, or Ti) and
form ?ne precipitates of nitride compounds in a near-surface layer. The hardness of the surface layer
depends on the types of nitrides formed. The source of nitrogen can be a hot gas (usually ammonia) or
a plasma. Nitrocarburizing and boronizing are related processes in which nitrogen or boron atoms diffuse
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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