is a registered trademark
of Special Metals Corporation
that refers to a family of austenitic nickel
. Inconel alloys are typically used in high temperature applications. It is often referred to in English as "Inco" (or occasionally "Iconel").
Inconel alloys are oxidation
resistant materials well suited for service in extreme environments. When heated, Inconel forms a thick, stable, passivating
oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high temperature applications where aluminum
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
Nb or gamma prime (γ'). Gamma prime forms small cubic crystals that inhibit slip and creep
effectively at elevated temperatures.
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 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
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.
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. The most common way to weld inconel is by using a TIG
welder with the appropriate filler metal.
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, steam generators in nuclear pressurized water reactors
, natural gas progessing with contaminants such as H2
S and CO2
, firearm sound suppressor
blast baffles, and Formula One
North American Aviation constructed the skin of the X-15 rocket plane out of an Inconel alloy known as "Inconel X".
- 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