Cobalt-based superalloy is an austenitic superalloy with a cobalt content of 40~65%. It has a certain high temperature strength, good thermal corrosion resistance and oxidation resistance under 730~1100 conditions. It is suitable for making the guide blade and nozzle guide vane of aviation jet engine, industrial gas turbine, Marine gas turbine and diesel engine nozzle.

Grade

Typical cobalt-base superalloys include Hayness188,Haynes25(L-605),Alloy S-816,UMCo-50,MP-159,FSX-414,X-40,Stellite6B, etc. Different from other superalloys, cobalt-based superalloys are not strengthened by orderly precipitated phases firmly bonded to the matrix, but by solid solution strengthened austenitic fcc matrix and matrix with a small amount of carbide distributed in the casting of cobalt-based superalloys, however, to a large extent rely on carbide strengthened pure cobalt crystals in 417 The following are densely packed hexagonal (hcp) crystal structures that convert to fcc at higher temperatures To avoid this transition when used in cobalt-based superalloys, virtually all cobalt-based superalloys are alloyed by nickel in order to stabilize the tissue in the temperature range from room temperature to melting point Cobalt-based superalloys have a flat fracture stress-temperature relationship, but at 1000 The above showed superior thermal corrosion resistance at higher temperatures than other alloys, possibly due to the high chromium content of the alloy, which is a characteristic of this class

Development

Version:1.0 StartHTML:0000000107 EndHTML:0000004068 StartFragment:0000000127 EndFragment:0000004050 At the end of the 30s of the 20th century, due to the need for turbochargers for piston aero engines, the development of cobalt-based superalloys began. In 1942, the United States was the first to successfully manufacture turbocharger blades from the dental metal material Vitallium (Co-27Cr-5Mo-0.5Ti). During use, this alloy continues to precipitate the carbide phase and become brittle. Therefore, the carbon content of the alloy is reduced to 0.3%, and 2.6% nickel is added at the same time to improve the solubility of the carbide-forming elements in the matrix, so that HA-21 alloys are developed. At the end of the 40s, the X-40 and HA-21 made cast turbine blades and guide vanes for aerojet engines and turbochargers, the operating temperature of which reached 850-870 ° C. S-816, which appeared in 1953 as a forged turbine blade, is an alloy reinforced with a solid solution of various refractory elements. From the late 50s to the late 60s, 4 cast cobalt-based alloys were widely used in the United States: WI-52, X-45, Mar-M509 and FSX-414. Deformed cobalt-based alloys are mostly plates, such as L-605, which are used to make combustion chambers and conduits. HA-188, which appeared in 1966, improved antioxidant properties due to its lanthanum content. The cobalt-based alloy used in the USSR to make guide blades ∏K4, equivalent to HA-21. The development of cobalt-based alloys should consider the resource situation of cobalt. Cobalt is an important strategic resource, and most countries in the world are deficient in cobalt, so that the development of cobalt-based alloys is limited.
Generally, cobalt-based superalloys lack a common lattice strengthening phase, and although the medium-temperature strength is low (only 50-75% of nickel-based alloys), it has high strength, good thermal fatigue resistance, thermal corrosion resistance and wear resistance at higher than 980 °C, and good weldability. It is suitable for the production of guide vanes and nozzle guide vanes of aerojet engines, industrial gas turbines, ship gas turbines and diesel engine nozzles.

Performance

The carbide in cobalt-based superalloy has good thermal stability. When the temperature rises, the carbide agglomeration and growth rate is slower than that of the γ phase in nickel-based alloy, and the temperature of re-dissolution in the matrix is higher (up to 1100). Therefore, the strength of cobalt-based alloy generally declines slowly when the temperature rises Cobalt alloys have excellent thermal corrosion resistance. It is generally believed that cobalt alloys are superior to nickel alloys in this respect because the sulfide melting point of cobalt (e.g., Co-Co4S3 eutectic,877) is higher than that of nickel (e.g., Ni-Ni3S2 eutectic, 645), and the diffusion rate of sulfur in cobalt is much lower than that in nickel And because most cobalt-based alloys have higher chromium content than nickel-based alloys, the surface of the alloy can be formed to resist alkali metal sulfates (such as the Cr2O3 coating corroded by Na2SO4), but cobalt-based superalloys usually have much lower oxidation resistance than nickel-based alloys.

In this paper, you’ll learn the basics of high-performance superalloys, and be provided with some guidance for their use in new product applications and improved product design.

Superalloys are cobalt-, iron-, or nickel-based alloys. They are designed for high strength at elevated temperatures; creep properties; oxidation resistance; and corrosion resistance. The primary application for such alloys is in turbine engines, where creep is typically the lifetime-limiting factor in gas turbine blades.

Cobalt-based alloys are non-ferrous magnetic alloys with high strength and toughness, excellent corrosion and oxidation resistance, and high temperature strength. Cobalt’s properties result in its use for alloys in jet engine components, prosthetics, and magnets. Cobalt-based superalloys potentially possess superior hot-corrosion, oxidation, and wear resistance compared to Ni-based superalloys. But cobalt-based superalloys also typically have a lower strength at high temperatures than Ni-based superalloys. Additionally, cobalt-based alloys are the most expensive, with a current spot price for cobalt at $17.60/lb (October 2020), with a seven-year range fluctuating from $10.00 to $40.00/lb (2013-2020).

Cobalt Alloys

• FSX-414
• HS-1, HS-4, HS-6B, HS-12, HS-19, HS-21, HS-25, HS-31
• Haynes 188
• Jetalloy
• Mar M-302, M-509, M-905
• Ultimet

Iron-based alloys contain iron as the base metal. This category includes carbon steels, alloy steels, stainless steels, cast iron, maraging steel, and other specialty iron-based alloys with varying properties. Only a few of these alloys could be considered as superalloys. These are the least expensive alloy. Pricing is based not so much on iron content, but the other elements.

Iron-Based Alloys and Special

• Kovar
• Invar
• Nitronic 40, 50, 60

Nickel-based alloys are non-ferrous metals with high strength and toughness, excellent corrosion resistance, and superior elevated temperature properties. Nickel can also be magnetized. Nickel-based superalloys are the most common alloy class, resulting a wide range of applications including jet engine components, chemical process equipment, magnets, heating element components and electrical resistance elements. Nickel is also a useful alloying element in many other stainless, tool steels, maraging, and other alloy steels. Nickel-based alloys are the mid-priced superalloys, with a current spot price for nickel at $7.10/lb., and a seven-year range fluctuating from $4.00 to $10.00/lb. (2013-2020).

Nickel Alloys

• Inconel 600, 601, 617 625, 690
• Inconel 702, 713, 718, 722, 738, 750
• Inconel 800, 801, 825
• Inconel 901, 903
• Hastelloy B, B-2, C-4, C-22, C-276, C-2000, F, G, N, R, S, W, X
• Haynes 25, 36, 214, 230, 556
• HR-160, IN-100, MP35N, B-1900
• Mar M-002, M-200, M-246, M-247, M-421
• Monel 400, 405, 411, 500
• Mu Metal
• NichromeV
• Nickel 200
• Nim 101, 263
• Nimonic 75, 80A, 90
• Ni-Span 902
• Rene 41, 77, 80, 95, 125
• Supertherm
• Udimet 500, 520
• Waspaloy

Many superalloys are trademarked and use alternate names. Inconel^™625 of Special Metals Corporation is also called Inco 625, Alloy 625, Nickel 625, Chornin^® 625, Altemp^® 625, Nickelvac^® 625, Haynes^® 625, Nicrofer^® 6020; or is typically specified by American Military Standard (AMS) material designation. Many superalloys can be purchased in annealed and solution-heat-treated condition from the distributor or manufacturer.

For round bar/billet Inconel 625

AMS 5666 Condition A

Typical solution heat treatments are:

Solution 1950F and precipitation (age) hardened 1400F

Solution 2150F and precipitation (age) hardened 1200F

Inconel’s high temperature strength is developed by solid-solution strengthening or precipitation hardening, depending on the alloy.

Superalloys are the materials which have made very-high-temperature engineering technologies possible. But keep in mind, these alloys, like Inconel 625, are also very good for other applications.

Mild corrosive environments such as the atmosphere, fresh or salt water, neutral salts and alkaline environment have almost no attack.

In severe corrosive environments, the combination of nickel and chromium provides resistance to oxidizing chemicals, and molybdenum content supplies resistance to non-oxidizing environments. Further, elements such as niobium are stabilized for welding sensitization, thereby preventing intergranular cracking. This makes it one of the most highly utilized superalloys.

Finding the best alloy for an application is technically difficult, but there are resources to select the best for your application.

Protomatic Can Help

Protomatic is a CNC machine shop specializing in prototype and short-run CNC parts. From aerospace parts machining to medical device machining, everything is designed and made with Life-Saving Precision.

Nickel base Superalloys service at high temperatures, particularly in the hot zones of gas turbine engine. These materials allow the turbine to operate more efficiently by withstanding higher temperatures. Turbine Inlet Temperature (TIT) depends on the temperature capability of first stage high-pressure turbine blade made of nickel base superalloys exclusively. Single crystal Nickel base turbine blade is free from g/ g¢ grain boundaries; boundaries are easy diffusion paths and therefore reduce the resistance of the material to creep deformation. Experimental investigation carried out by using Different scrap of turbine blades with different chemical compositions were melted aiming to control the chemical composition of the product alloy, leading to a steel alloy called iron base superalloy with nickel content (24.3%) and chromium content (13.2%) this new alloy has almost the same mechanical properties of nickel base superalloy of higher price. This new alloy can be used for production of turbine blades for small gas turbine engines less than 200 KW. Solidification behavior of stepped cast specimen of nickel base superalloy was studded by using three different cast thicknesses size. The results and conclusion of this work show that the higher the cooling rate is the better the mechanical properties. The results also show that the increase of cobalt and titanium contents of nickel base alloy from 1.08 & 9.31 and 2.68 & 10.78 respectively leads to an increase in ultimate tensile strength, yield strength and hardness. Microstructure investigation of nickel base superalloys was conducted on all samples, the results show the continuous matrix (g) and the primary strengthening phase (g¢), the microstructure change from dendrite structure to a fine cellular one by increasing titanium percent content.

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