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Inconel 718 round barInconel is a nickel-chromium-based superalloy often utilized in extreme environments where components are subjected to high temperature, pressure or mechanical loads. Inconel alloys are oxidation- and corrosion-resistant. 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 and steel would succumb to creep as a result of thermally-induced crystal vacancies. Inconel's high-temperature strength is developed by solid solution strengthening or precipitation hardening, depending on the alloy.[1][2]
Inconel alloys are typically used in high temperature applications. Common trade names for various Inconel alloys include:
History
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The Inconel family of alloys was first developed before December , when its trademark was registered by the US company International Nickel Company of Delaware and New York.[5][6] A significant early use was found in support of the development of the Whittle jet engine,[7] during the s by research teams at Henry Wiggin & Co of Hereford, England a subsidiary of the Mond Nickel Company,[8] which merged with Inco in . The Hereford Works and its properties including the Inconel trademark were acquired in by Special Metals Corporation.[9]
Specific data
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Alloy Solidus °C (°F) Liquidus °C (°F) Inconel 600[10] (2,469) (2,575) Inconel 617[11][12] (2,430) (2,511) Inconel 625[13] (2,350) (2,460) Inconel 690[14] (2,449) (2,511) Inconel 718[15] (2,300) (2,437) Inconel X-750[16] (2,530) (2,610)Composition
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Inconel alloys vary widely in their compositions, but all are predominantly nickel, with chromium as the second element.
Inconel Element, proportion by mass (%) Ni Cr Fe Mo Nb & Ta Co Mn Cu Al Ti Si C S P B 600[17] &#;72.0[a] 14.0&#;17.0 6.0&#;10.0 &#; &#;1.0 &#;0.5 &#;0.5 &#;0.15 &#;0.015 617[18] 44.2&#;61.0 20.0&#;24.0 &#;3.0 8.0&#;10.0 10.0&#;15.0 &#;0.5 &#;0.5 0.8&#;1.5 &#;0.6 &#;0.5 0.05&#;0.15 &#;0.015 &#;0.015 &#;0.006 625[19] &#;58.0 20.0&#;23.0 &#;5.0 8.0&#;10.0 3.15&#;4.15 &#;1.0 &#;0.5 &#;0.4 &#;0.4 &#;0.5 &#;0.1 &#;0.015 &#;0.015 690[20] &#;58 27&#;31 7&#;11 &#;0.50 &#;0.50 &#;0.50 &#;0.05 &#;0.015 Nuclear grade 690[20] &#;58 28&#;31 7&#;11 &#;0.10 &#;0.50 &#;0.50 &#;0.50 &#;0.04 &#;0.015 718[1] 50.0&#;55.0 17.0&#;21.0 Balance 2.8&#;3.3 4.75&#;5.5 &#;1.0 &#;0.35 &#;0.3 0.2&#;0.8 0.65&#;1.15 &#;0.35 &#;0.08 &#;0.015 &#;0.015 &#;0.006 X-750[21] &#;70.0 14.0&#;17.0 5.0&#;9.0 0.7&#;1.2 &#;1.0 &#;1.0 &#;0.5 0.4&#;1.0 2.25&#;2.75 &#;0.5 &#;0.08 &#;0.01Properties
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When heated, Inconel forms a thick and stable passivating oxide layer protecting the surface from further attack. Inconel retains strength over a wide temperature range, attractive for high-temperature applications where aluminium 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 Ni3Nb or gamma double prime (γ&#;). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures. The formation of gamma-prime crystals increases over time, especially after three hours of a heat exposure of 850 °C (1,560 °F), and continues to grow after 72 hours of exposure.[22]
Strengthening mechanisms
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The most prevalent hardening mechanisms for Inconel alloys are precipitate strengthening and solid solution strengthening. In Inconel alloys, one of the two often dominates. For alloys like Inconel 718, precipitate strengthening is the main strengthening mechanism. The majority of strengthening comes from the presence of gamma double prime (γ&#;) precipitates.[23][24][25][26] Inconel alloys have a γ matrix phase with an FCC structure.[25][27][28][29] γ&#; precipitates are made of Ni and Nb, specifically with a Ni3Nb composition. These precipitates are fine, coherent, disk-shaped, intermetallic particles with a tetragonal structure.[24][25][26][27][30][31][32][33]
Secondary precipitate strengthening comes from gamma prime (γ') precipitates. The γ' phase can appear in multiple compositions such as Ni3(Al, Ti).[24][25][26] The precipitate phase is coherent and has an FCC structure, like the γ matrix;[33][27][30][31][32] The γ' phase is much less prevalent than γ&#;. The volume fraction of the γ&#; and γ' phases are approximately 15% and 4% after precipitation, respectively.[24][25] Because of the coherency between the γ matrix and the γ' and γ&#; precipitates, strain fields exist that obstruct the motion of dislocations. The prevalence of carbides with MX(Nb, Ti)(C, N) compositions also helps to strengthen the material.[25] For precipitate strengthening, elements like niobium, titanium, and tantalum play a crucial role.[34]
Because the γ&#; phase is metastable, over-aging can result in the transformation of γ&#; phase precipitates to delta (δ) phase precipitates, their stable counterparts.[25][27] The δ phase has an orthorhombic structure, a Ni3(Nb, Mo, Ti) composition, and is incoherent.[35][29] As a result, the transformation of γ&#; to δ in Inconel alloys leads to the loss of coherency strengthening, making for a weaker material. That being said, in appropriate quantities, the δ phase is responsible for grain boundary pinning and strengthening.[33][32][29]
Another common phase in Inconel alloys is the Laves intermetallic phase. Its compositions are (Ni, Cr, Fe)x(Nb, Mo, Ti)y and NiyNb, it is brittle, and its presence can be detrimental to the mechanical behavior of Inconel alloys.[27][33][36] Sites with large amounts of Laves phase are prone to crack propagation because of their higher potential for stress concentration.[31] Additionally, due to its high Nb, Mo, and Ti content, the Laves phase can exhaust the matrix of these elements, ultimately making precipitate and solid-solution strengthening more difficult.[32][36][28]
For alloys like Inconel 625, solid-solution hardening is the main strengthening mechanism. Elements like Mo are important in this process. Nb and Ta can also contribute to solid solution strengthening to a lesser extent.[34] In solid solution strengthening, Mo atoms are substituted into the γ matrix of Inconel alloys. Because Mo atoms have a significantly larger radius than those of Ni (209 pm and 163 pm, respectively), the substitution creates strain fields in the crystal lattice, which hinder the motion of dislocations, ultimately strengthening the material.
The combination of elemental composition and strengthening mechanisms is why Inconel alloys can maintain their favorable mechanical and physical properties, such as high strength and fatigue resistance, at elevated temperatures, specifically those up to 650°C.[23]
Machining
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Inconel is a difficult metal to shape and to machine using traditional cold forming techniques due to rapid work hardening. After the first machining pass, work hardening tends to plastically deform either the workpiece or the tool on subsequent passes. For this reason, age-hardened Inconels such as 718 are typically 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 "solutionized" form,[clarification needed] with only the final steps being performed after age hardening. However some claim[by whom?] that Inconel can be machined extremely quickly with very fast spindle speeds using a multifluted ceramic tool with small width of cut at high feed rates as this causes localized heating and softening in front of the flute.
External threads are machined using a lathe to "single-point" the threads or by rolling the threads in the solution treated condition (for hardenable alloys) using a screw machine. Inconel 718 can also be roll-threaded after full aging by using induction heat to 700 °C (1,290 °F) without increasing the grain size.[citation needed] Holes with internal threads are made by threadmilling. Internal threads can also be formed using a sinker electrical discharge machining (EDM).[citation needed]
Joining
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Welding of some Inconel alloys (especially the gamma prime precipitation hardened family; e.g., Waspaloy and X-750) can be difficult due to cracking and microstructural segregation of alloying elements in the heat-affected zone. However, several alloys such as 625 and 718 have been designed to overcome these problems. The most common welding methods are gas tungsten arc welding and electron-beam welding.[37]
Uses
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Delphin 3.0 rocket engine, used on Astra Rocket. 3D-printed in InconelInconel is often encountered in extreme environments. It is common in gas turbine blades, seals, and combustors, as well as turbocharger rotors and seals, electric submersible well pump motor shafts, high temperature fasteners, chemical processing and pressure vessels, heat exchanger tubing, steam generators and core components in nuclear pressurized water reactors,[38] natural gas processing with contaminants such as H2S and CO2, firearm sound suppressor blast baffles, and Formula One, NASCAR, NHRA, and APR, LLC exhaust systems.[39][40] It is also used in the turbo system of the 3rd generation Mazda RX7, and the exhaust systems of high powered Wankel engine and Norton motorcycles where exhaust temperatures reach more than 1,000 °C (1,830 °F).[41] Inconel is increasingly used in the boilers of waste incinerators.[42] The Joint European Torus and DIII-D tokamaks' vacuum vessels are made of Inconel.[43] Inconel 718 is commonly used for cryogenic storage tanks, downhole shafts, wellhead parts,[44] and in the aerospace industry -- where it has become a prime candidate material for constructing heat resistant turbines.[45]
Aerospace
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Automotive
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Rolled Inconel was frequently used as the recording medium by engraving in black box recorders on aircraft.[64]
Alternatives to the use of Inconel in chemical applications such as scrubbers, columns, reactors, and pipes are Hastelloy, perfluoroalkoxy (PFA) lined carbon steel or fiber reinforced plastic.
Inconel alloys
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Alloys of Inconel include:
In age hardening or precipitation strengthening varieties, alloying additions of aluminum and titanium combine with nickel to form the intermetallic compound Ni3(Ti,Al) or gamma prime (γ&#;). Gamma prime forms small cubic crystals that inhibit slip and creep effectively at elevated temperatures.
See also
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References
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Most Inconel are nickel - chromium alloys. Both nickel and chromium have good corrosion resistance at high temperatures. Among them, chromium has excellent antioxidant properties. Therefore, Inconel alloys are often used in high temperature corrosion resistant applications. Some Inconel alloys are also used for high strength applications. In this article, we will introduce the different types of Inconel alloys one by one.
Inconel Types
Inconel 600 is a solid solution strengthened heat-resistant and corrosion-resistant alloy with good high temperature corrosion resistance, oxidation resistance, hot and cold processing properties, low temperature mechanical properties, cold and hot fatigue properties. It features high strength under 650 ° C, good formability and easy soldering, suitable for heat treatment and chemical processing industrial equipment.
600
Si
C
Mn
Cu
Fe
Cr
Ni
Inconel 601 features excellent oxidation resistance at high temperature, good resistance to carbonization, good resistance to oxidized sulfur-containing atmosphere, good mechanical properties at room temperature and high temperature, good stress corrosion crack resistance due to controlled carbon content and grain size. Inconel 601 exhibits high creep rupture strength, suitable for applications with temperature above 500 °C.
601
Si
C
Mn
Al
Cu
Fe
Cr
Ni
Inconel 601GC is a grain-controlled version of Inconel 601.
601GC
Si
Mn
Al
Cu
Fe
Cr
Ni
Inconel 617 is a nickel-chromium-cobalt-molybdenum alloy with excellent mechanical properties at high temperatures. This alloy also exhibits high-temperature corrosion resistance such as oxidation and carbonization.
617
Si
C
Mn
Al
Ti
Cu
Co
Mo
Fe
Cr
Ni
Inconel 625 features good corrosion and oxidation resistance, good tensile properties and fatigue properties from low temperature to 980 ° C, as well as stress corrosion resistance in salt atmosphere.
625
Si
C
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Al
Ti
Co
Ta
Mo
Fe
Cr
Ni
Inconel 686 is a low carbon nickel-chromium-molybdenum-tungsten alloy with remarkable resistance to general corrosion, stress corrosion cracking, pitting and crevice corrosion, oxidization, reducing and mixed acids. It also exhibits pronounced corrosion resistance in environments containing halides. Besides, Inconel 686 is resistant to sea water and other marine environments, widely used in chemical production, marine, air pollution control (flue gas desulfurization) industry, pulp and paper industry and waste management.
686
Mn
W
Mo
Fe
Cr
Ni
Inconel 690 is resistance to chloride corrosion, high temperature and high-pressure water stress corrosion, strong oxidizing medium and HNO2-HF mixed corrosion. This alloy is commonly used in nuclear waste treatment plants, steam generators, and nitric acid resistant parts.
690
Si
Cu
Fe
Cr
Ni
Inconel 718 is a precipitation-hardening Ni-Cr-Fe alloy with addition of the niobium and molybdenum. It features high strength and good toughness under temperatures below 650 °C. Inconel 718 exhibits corrosion resistance in both low and high temperature environments. Delivery state can be solution treatment or precipitation hardening.
718
Si
C
Al
Ti
Co
Nb
Ta
Mo
Fe
Cr
Ni
Inconel 725 is a type of nickel-chromium-molybdenum-niobium alloy with excellent corrosion resistance and stress corrosion resistance. Aging heat treatment can greatly improve the alloy strength, ductility and tensile strength.
725
Si
Al
Ti
Nb
Mo
Fe
Cr
Ni
Inconel 740H obtains age hardening by precipitation of the gamma primary and secondary phases. After aging strengthening, the 740H alloy exhibits excellent high temperature strength under temperatures below 850 °C. High content of chromium and cobalt contained within gives the 740H alloy excellent oxidation resistance, carbonization and vulcanization at high temperatures.
740H
Si
Mn
Al
Ti
Cu
Co
Mo
Fe
Cr
Ni
Inconel X-750 exhibits good corrosion resistance and oxidation resistance, as well as good strength below 980 °C. In addition, Inconel X-750 also has good low temperature performance and molding performance, mainly used as aerospace and industrial gas turbine components.
X-750
Si
C
Mn
Al
Ti
Cu
Co
Fe
Cr
Ni
Inconel 751 is a type of precipitation hardening super alloy similar to alloy 750. It features good wear resistance, strength and corrosion resistance as well as hot hardness under high temperatures, mainly used for exhaust valves on internal combustion engines.
751
Si
C
Mn
Al
Ti
Cu
Co
Fe
Cr
Ni
Inconel 783 is an oxidation-resistant super alloy with a low coefficient of thermal expansion, developed specifically for turbine applications. With the addition of niobium and aluminum, the strength of the 783 alloy can be enhanced by precipitation hardening heat treatment. In addition, the aluminum contained within gives it excellent oxidation resistance under high temperatures. The density of 783 alloy is smaller than that of super alloy 718 by roughly 5%.
783
Si
Al
Ti
Cu
Co
Nb
Fe
Cr
Ni
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