Inconel
1568958
225779730
2008-07-15T10:46:55Z
The Yeti
417539
/* Uses */
'''Inconel''' is a registered [[trademark]] of [[Special Metals Corporation]] that refers to a family of [[austenitic]] [[nickel]]-based [[superalloys]]. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco" (or occasionally "Iconel").
==Properties==
Inconel alloys are [[oxidation]] and [[corrosion]] resistant materials well suited for service in extreme environments. When heated, Inconel forms a thick, stable, [[passivation|passivating]] oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where [[aluminum]] and [[steel]] would succumb to creep as a result of thermally-induced crystal vacancies (see [[Arrhenius equation]]). Inconel's high temperature strength is developed by [[solid solution]] strengthening or [[precipitation strengthening]], depending on the alloy. In age hardening or precipitation strengthening varieties, small amounts of [[niobium]] combine with nickel to form the [[intermetallic]] compound Ni<sub>3</sub>Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and [[creep (deformation)|creep]] effectively at elevated temperatures.
==Machining==
Inconel is a difficult metal to shape and machine using traditional techniques due to rapid [[work hardening]]. After the first machining pass, work hardening tends to elastically deform either the workpiece or the tool on subsequent passes. For this reason, age-hardened Inconels such as 718 are machined using an aggressive but slow cut with a hard tool, minimizing the number of passes required. Alternatively, the majority of the machining can be performed with the workpiece in a solutionised form, with only the final steps being performed after age-hardening. External [[screw thread|threads]] are machined using a [[lathe]] to "single point" the threads, or by rolling the threads using a [[screw machine]]. Holes with internal threads are made by [[welding]] or [[brazing]] threaded inserts made of [[stainless steel]]. Cutting of plate is often done with a [[waterjet cutter]].
Internal threads can also be cut by single point method on lathe, or by threadmilling on machining center.
New whisker reinforced ceramic cutters are also used to machine nickel alloys. They remove material at a rate typically 8X faster than carbide cutters.
==Joining==
Welding inconel alloys is difficult due to cracking and microstructural segregation of alloying elements in the [[heat affected zone]]. However, several alloys have been designed to overcome these problems.{{Fact|date=March 2007}}
==Uses==
Inconel is often encountered in extreme environments. It is common in [[gas turbine]] blades, seals, and combustors, as well as [[turbocharger]] rotors and seals, high temperature fasteners, chemical processing and pressure vessels, [[heat exchanger]] tubing, natural gas progessing with contaminants such as H<sub>2</sub>S and CO<sub>2</sub>, [[firearm]] [[suppressor|sound suppressor]] blast baffles, and [[Formula One racing|Formula One]] exhaust systems.<ref>[http://www.specialmetals.com/power.php Power Generation], Special Metals Corporation.</ref><ref>[http://www.specialmetals.com/chemical.php Chemical Processing], Special Metals Corporation.</ref><ref>[http://www.goodfabs.com/about.htm About Good Fabrications] ("Performance inconel exhaust manufacturers for racecars").</ref>
[[North American Aviation]] constructed the skin of the [[X-15]] rocket plane out of an Inconel alloy known as "Inconel X".<ref>Robert S. Houston, Richard P. Hallion, and Ronald G. Boston, [http://www.hq.nasa.gov/office/pao/History/hyperrev-x15/ch-0.html EDITOR'S INTRODUCTION, "Transiting from Air to Space: The North American X-15"], ''The Hypersonic Revolution: Case Studies in the History of Hypersonic Technology'', Air Force History and Museums Program, 1998. NASA.gov.</ref>
==Inconel alloys==
* Inconel 600: Solid solution strengthened
* Inconel 625: Acid resistant, good weldability
* Inconel 690: Low cobalt content for nuclear applications
* Inconel 718: Gamma double prime strengthened with good weldability
* Inconel 939: Gamma prime strengthened with good weldability
==References==
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[[Category:Metallurgy]]
[[Category:Nickel alloys]]
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